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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

1	<?xml version="1.0" encoding="UTF-8"?>
2	<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3		"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
4	
5	<book id="drmDevelopersGuide">
6	  <bookinfo>
7	    <title>Linux DRM Developer's Guide</title>
8	
9	    <authorgroup>
10	      <author>
11		<firstname>Jesse</firstname>
12		<surname>Barnes</surname>
13		<contrib>Initial version</contrib>
14		<affiliation>
15		  <orgname>Intel Corporation</orgname>
16		  <address>
17		    <email>jesse.barnes@intel.com</email>
18		  </address>
19		</affiliation>
20	      </author>
21	      <author>
22		<firstname>Laurent</firstname>
23		<surname>Pinchart</surname>
24		<contrib>Driver internals</contrib>
25		<affiliation>
26		  <orgname>Ideas on board SPRL</orgname>
27		  <address>
28		    <email>laurent.pinchart@ideasonboard.com</email>
29		  </address>
30		</affiliation>
31	      </author>
32	    </authorgroup>
33	
34	    <copyright>
35	      <year>2008-2009</year>
36	      <year>2012</year>
37	      <holder>Intel Corporation</holder>
38	      <holder>Laurent Pinchart</holder>
39	    </copyright>
40	
41	    <legalnotice>
42	      <para>
43		The contents of this file may be used under the terms of the GNU
44		General Public License version 2 (the "GPL") as distributed in
45		the kernel source COPYING file.
46	      </para>
47	    </legalnotice>
48	
49	    <revhistory>
50	      <!-- Put document revisions here, newest first. -->
51	      <revision>
52		<revnumber>1.0</revnumber>
53		<date>2012-07-13</date>
54		<authorinitials>LP</authorinitials>
55		<revremark>Added extensive documentation about driver internals.
56		</revremark>
57	      </revision>
58	    </revhistory>
59	  </bookinfo>
60	
61	<toc></toc>
62	
63	  <!-- Introduction -->
64	
65	  <chapter id="drmIntroduction">
66	    <title>Introduction</title>
67	    <para>
68	      The Linux DRM layer contains code intended to support the needs
69	      of complex graphics devices, usually containing programmable
70	      pipelines well suited to 3D graphics acceleration.  Graphics
71	      drivers in the kernel may make use of DRM functions to make
72	      tasks like memory management, interrupt handling and DMA easier,
73	      and provide a uniform interface to applications.
74	    </para>
75	    <para>
76	      A note on versions: this guide covers features found in the DRM
77	      tree, including the TTM memory manager, output configuration and
78	      mode setting, and the new vblank internals, in addition to all
79	      the regular features found in current kernels.
80	    </para>
81	    <para>
82	      [Insert diagram of typical DRM stack here]
83	    </para>
84	  </chapter>
85	
86	  <!-- Internals -->
87	
88	  <chapter id="drmInternals">
89	    <title>DRM Internals</title>
90	    <para>
91	      This chapter documents DRM internals relevant to driver authors
92	      and developers working to add support for the latest features to
93	      existing drivers.
94	    </para>
95	    <para>
96	      First, we go over some typical driver initialization
97	      requirements, like setting up command buffers, creating an
98	      initial output configuration, and initializing core services.
99	      Subsequent sections cover core internals in more detail,
100	      providing implementation notes and examples.
101	    </para>
102	    <para>
103	      The DRM layer provides several services to graphics drivers,
104	      many of them driven by the application interfaces it provides
105	      through libdrm, the library that wraps most of the DRM ioctls.
106	      These include vblank event handling, memory
107	      management, output management, framebuffer management, command
108	      submission &amp; fencing, suspend/resume support, and DMA
109	      services.
110	    </para>
111	
112	  <!-- Internals: driver init -->
113	
114	  <sect1>
115	    <title>Driver Initialization</title>
116	    <para>
117	      At the core of every DRM driver is a <structname>drm_driver</structname>
118	      structure. Drivers typically statically initialize a drm_driver structure,
119	      and then pass it to one of the <function>drm_*_init()</function> functions
120	      to register it with the DRM subsystem.
121	    </para>
122	    <para>
123	      The <structname>drm_driver</structname> structure contains static
124	      information that describes the driver and features it supports, and
125	      pointers to methods that the DRM core will call to implement the DRM API.
126	      We will first go through the <structname>drm_driver</structname> static
127	      information fields, and will then describe individual operations in
128	      details as they get used in later sections.
129	    </para>
130	    <sect2>
131	      <title>Driver Information</title>
132	      <sect3>
133	        <title>Driver Features</title>
134	        <para>
135	          Drivers inform the DRM core about their requirements and supported
136	          features by setting appropriate flags in the
137	          <structfield>driver_features</structfield> field. Since those flags
138	          influence the DRM core behaviour since registration time, most of them
139	          must be set to registering the <structname>drm_driver</structname>
140	          instance.
141	        </para>
142	        <synopsis>u32 driver_features;</synopsis>
143	        <variablelist>
144	          <title>Driver Feature Flags</title>
145	          <varlistentry>
146	            <term>DRIVER_USE_AGP</term>
147	            <listitem><para>
148	              Driver uses AGP interface, the DRM core will manage AGP resources.
149	            </para></listitem>
150	          </varlistentry>
151	          <varlistentry>
152	            <term>DRIVER_REQUIRE_AGP</term>
153	            <listitem><para>
154	              Driver needs AGP interface to function. AGP initialization failure
155	              will become a fatal error.
156	            </para></listitem>
157	          </varlistentry>
158	          <varlistentry>
159	            <term>DRIVER_PCI_DMA</term>
160	            <listitem><para>
161	              Driver is capable of PCI DMA, mapping of PCI DMA buffers to
162	              userspace will be enabled. Deprecated.
163	            </para></listitem>
164	          </varlistentry>
165	          <varlistentry>
166	            <term>DRIVER_SG</term>
167	            <listitem><para>
168	              Driver can perform scatter/gather DMA, allocation and mapping of
169	              scatter/gather buffers will be enabled. Deprecated.
170	            </para></listitem>
171	          </varlistentry>
172	          <varlistentry>
173	            <term>DRIVER_HAVE_DMA</term>
174	            <listitem><para>
175	              Driver supports DMA, the userspace DMA API will be supported.
176	              Deprecated.
177	            </para></listitem>
178	          </varlistentry>
179	          <varlistentry>
180	            <term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
181	            <listitem><para>
182	              DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler
183	              managed by the DRM Core. The core will support simple IRQ handler
184	              installation when the flag is set. The installation process is
185	              described in <xref linkend="drm-irq-registration"/>.</para>
186	              <para>DRIVER_IRQ_SHARED indicates whether the device &amp; handler
187	              support shared IRQs (note that this is required of PCI  drivers).
188	            </para></listitem>
189	          </varlistentry>
190	          <varlistentry>
191	            <term>DRIVER_GEM</term>
192	            <listitem><para>
193	              Driver use the GEM memory manager.
194	            </para></listitem>
195	          </varlistentry>
196	          <varlistentry>
197	            <term>DRIVER_MODESET</term>
198	            <listitem><para>
199	              Driver supports mode setting interfaces (KMS).
200	            </para></listitem>
201	          </varlistentry>
202	          <varlistentry>
203	            <term>DRIVER_PRIME</term>
204	            <listitem><para>
205	              Driver implements DRM PRIME buffer sharing.
206	            </para></listitem>
207	          </varlistentry>
208	          <varlistentry>
209	            <term>DRIVER_RENDER</term>
210	            <listitem><para>
211	              Driver supports dedicated render nodes.
212	            </para></listitem>
213	          </varlistentry>
214	        </variablelist>
215	      </sect3>
216	      <sect3>
217	        <title>Major, Minor and Patchlevel</title>
218	        <synopsis>int major;
219	int minor;
220	int patchlevel;</synopsis>
221	        <para>
222	          The DRM core identifies driver versions by a major, minor and patch
223	          level triplet. The information is printed to the kernel log at
224	          initialization time and passed to userspace through the
225	          DRM_IOCTL_VERSION ioctl.
226	        </para>
227	        <para>
228	          The major and minor numbers are also used to verify the requested driver
229	          API version passed to DRM_IOCTL_SET_VERSION. When the driver API changes
230	          between minor versions, applications can call DRM_IOCTL_SET_VERSION to
231	          select a specific version of the API. If the requested major isn't equal
232	          to the driver major, or the requested minor is larger than the driver
233	          minor, the DRM_IOCTL_SET_VERSION call will return an error. Otherwise
234	          the driver's set_version() method will be called with the requested
235	          version.
236	        </para>
237	      </sect3>
238	      <sect3>
239	        <title>Name, Description and Date</title>
240	        <synopsis>char *name;
241	char *desc;
242	char *date;</synopsis>
243	        <para>
244	          The driver name is printed to the kernel log at initialization time,
245	          used for IRQ registration and passed to userspace through
246	          DRM_IOCTL_VERSION.
247	        </para>
248	        <para>
249	          The driver description is a purely informative string passed to
250	          userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
251	          the kernel.
252	        </para>
253	        <para>
254	          The driver date, formatted as YYYYMMDD, is meant to identify the date of
255	          the latest modification to the driver. However, as most drivers fail to
256	          update it, its value is mostly useless. The DRM core prints it to the
257	          kernel log at initialization time and passes it to userspace through the
258	          DRM_IOCTL_VERSION ioctl.
259	        </para>
260	      </sect3>
261	    </sect2>
262	    <sect2>
263	      <title>Driver Load</title>
264	      <para>
265	        The <methodname>load</methodname> method is the driver and device
266	        initialization entry point. The method is responsible for allocating and
267	        initializing driver private data, specifying supported performance
268	        counters, performing resource allocation and mapping (e.g. acquiring
269	        clocks, mapping registers or allocating command buffers), initializing
270	        the memory manager (<xref linkend="drm-memory-management"/>), installing
271	        the IRQ handler (<xref linkend="drm-irq-registration"/>), setting up
272	        vertical blanking handling (<xref linkend="drm-vertical-blank"/>), mode
273		setting (<xref linkend="drm-mode-setting"/>) and initial output
274		configuration (<xref linkend="drm-kms-init"/>).
275	      </para>
276	      <note><para>
277	        If compatibility is a concern (e.g. with drivers converted over from
278	        User Mode Setting to Kernel Mode Setting), care must be taken to prevent
279	        device initialization and control that is incompatible with currently
280	        active userspace drivers. For instance, if user level mode setting
281	        drivers are in use, it would be problematic to perform output discovery
282	        &amp; configuration at load time. Likewise, if user-level drivers
283	        unaware of memory management are in use, memory management and command
284	        buffer setup may need to be omitted. These requirements are
285	        driver-specific, and care needs to be taken to keep both old and new
286	        applications and libraries working.
287	      </para></note>
288	      <synopsis>int (*load) (struct drm_device *, unsigned long flags);</synopsis>
289	      <para>
290	        The method takes two arguments, a pointer to the newly created
291		<structname>drm_device</structname> and flags. The flags are used to
292		pass the <structfield>driver_data</structfield> field of the device id
293		corresponding to the device passed to <function>drm_*_init()</function>.
294		Only PCI devices currently use this, USB and platform DRM drivers have
295		their <methodname>load</methodname> method called with flags to 0.
296	      </para>
297	      <sect3>
298	        <title>Driver Private &amp; Performance Counters</title>
299	        <para>
300	          The driver private hangs off the main
301	          <structname>drm_device</structname> structure and can be used for
302	          tracking various device-specific bits of information, like register
303	          offsets, command buffer status, register state for suspend/resume, etc.
304	          At load time, a driver may simply allocate one and set
305	          <structname>drm_device</structname>.<structfield>dev_priv</structfield>
306	          appropriately; it should be freed and
307	          <structname>drm_device</structname>.<structfield>dev_priv</structfield>
308	          set to NULL when the driver is unloaded.
309	        </para>
310	        <para>
311	          DRM supports several counters which were used for rough performance
312	          characterization. This stat counter system is deprecated and should not
313	          be used. If performance monitoring is desired, the developer should
314	          investigate and potentially enhance the kernel perf and tracing
315	          infrastructure to export GPU related performance information for
316	          consumption by performance monitoring tools and applications.
317	        </para>
318	      </sect3>
319	      <sect3 id="drm-irq-registration">
320	        <title>IRQ Registration</title>
321	        <para>
322	          The DRM core tries to facilitate IRQ handler registration and
323	          unregistration by providing <function>drm_irq_install</function> and
324	          <function>drm_irq_uninstall</function> functions. Those functions only
325	          support a single interrupt per device, devices that use more than one
326	          IRQs need to be handled manually.
327	        </para>
328	        <sect4>
329	          <title>Managed IRQ Registration</title>
330	          <para>
331	            Both the <function>drm_irq_install</function> and
332		    <function>drm_irq_uninstall</function> functions get the device IRQ by
333		    calling <function>drm_dev_to_irq</function>. This inline function will
334		    call a bus-specific operation to retrieve the IRQ number. For platform
335		    devices, <function>platform_get_irq</function>(..., 0) is used to
336		    retrieve the IRQ number.
337	          </para>
338	          <para>
339	            <function>drm_irq_install</function> starts by calling the
340	            <methodname>irq_preinstall</methodname> driver operation. The operation
341	            is optional and must make sure that the interrupt will not get fired by
342	            clearing all pending interrupt flags or disabling the interrupt.
343	          </para>
344	          <para>
345	            The IRQ will then be requested by a call to
346	            <function>request_irq</function>. If the DRIVER_IRQ_SHARED driver
347	            feature flag is set, a shared (IRQF_SHARED) IRQ handler will be
348	            requested.
349	          </para>
350	          <para>
351	            The IRQ handler function must be provided as the mandatory irq_handler
352	            driver operation. It will get passed directly to
353	            <function>request_irq</function> and thus has the same prototype as all
354	            IRQ handlers. It will get called with a pointer to the DRM device as the
355	            second argument.
356	          </para>
357	          <para>
358	            Finally the function calls the optional
359	            <methodname>irq_postinstall</methodname> driver operation. The operation
360	            usually enables interrupts (excluding the vblank interrupt, which is
361	            enabled separately), but drivers may choose to enable/disable interrupts
362	            at a different time.
363	          </para>
364	          <para>
365	            <function>drm_irq_uninstall</function> is similarly used to uninstall an
366	            IRQ handler. It starts by waking up all processes waiting on a vblank
367	            interrupt to make sure they don't hang, and then calls the optional
368	            <methodname>irq_uninstall</methodname> driver operation. The operation
369	            must disable all hardware interrupts. Finally the function frees the IRQ
370	            by calling <function>free_irq</function>.
371	          </para>
372	        </sect4>
373	        <sect4>
374	          <title>Manual IRQ Registration</title>
375	          <para>
376	            Drivers that require multiple interrupt handlers can't use the managed
377	            IRQ registration functions. In that case IRQs must be registered and
378	            unregistered manually (usually with the <function>request_irq</function>
379	            and <function>free_irq</function> functions, or their devm_* equivalent).
380	          </para>
381	          <para>
382	            When manually registering IRQs, drivers must not set the DRIVER_HAVE_IRQ
383	            driver feature flag, and must not provide the
384		    <methodname>irq_handler</methodname> driver operation. They must set the
385		    <structname>drm_device</structname> <structfield>irq_enabled</structfield>
386		    field to 1 upon registration of the IRQs, and clear it to 0 after
387		    unregistering the IRQs.
388	          </para>
389	        </sect4>
390	      </sect3>
391	      <sect3>
392	        <title>Memory Manager Initialization</title>
393	        <para>
394	          Every DRM driver requires a memory manager which must be initialized at
395	          load time. DRM currently contains two memory managers, the Translation
396	          Table Manager (TTM) and the Graphics Execution Manager (GEM).
397	          This document describes the use of the GEM memory manager only. See
398	          <xref linkend="drm-memory-management"/> for details.
399	        </para>
400	      </sect3>
401	      <sect3>
402	        <title>Miscellaneous Device Configuration</title>
403	        <para>
404	          Another task that may be necessary for PCI devices during configuration
405	          is mapping the video BIOS. On many devices, the VBIOS describes device
406	          configuration, LCD panel timings (if any), and contains flags indicating
407	          device state. Mapping the BIOS can be done using the pci_map_rom() call,
408	          a convenience function that takes care of mapping the actual ROM,
409	          whether it has been shadowed into memory (typically at address 0xc0000)
410	          or exists on the PCI device in the ROM BAR. Note that after the ROM has
411	          been mapped and any necessary information has been extracted, it should
412	          be unmapped; on many devices, the ROM address decoder is shared with
413	          other BARs, so leaving it mapped could cause undesired behaviour like
414	          hangs or memory corruption.
415	  <!--!Fdrivers/pci/rom.c pci_map_rom-->
416	        </para>
417	      </sect3>
418	    </sect2>
419	  </sect1>
420	
421	  <!-- Internals: memory management -->
422	
423	  <sect1 id="drm-memory-management">
424	    <title>Memory management</title>
425	    <para>
426	      Modern Linux systems require large amount of graphics memory to store
427	      frame buffers, textures, vertices and other graphics-related data. Given
428	      the very dynamic nature of many of that data, managing graphics memory
429	      efficiently is thus crucial for the graphics stack and plays a central
430	      role in the DRM infrastructure.
431	    </para>
432	    <para>
433	      The DRM core includes two memory managers, namely Translation Table Maps
434	      (TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
435	      manager to be developed and tried to be a one-size-fits-them all
436	      solution. It provides a single userspace API to accommodate the need of
437	      all hardware, supporting both Unified Memory Architecture (UMA) devices
438	      and devices with dedicated video RAM (i.e. most discrete video cards).
439	      This resulted in a large, complex piece of code that turned out to be
440	      hard to use for driver development.
441	    </para>
442	    <para>
443	      GEM started as an Intel-sponsored project in reaction to TTM's
444	      complexity. Its design philosophy is completely different: instead of
445	      providing a solution to every graphics memory-related problems, GEM
446	      identified common code between drivers and created a support library to
447	      share it. GEM has simpler initialization and execution requirements than
448	      TTM, but has no video RAM management capabitilies and is thus limited to
449	      UMA devices.
450	    </para>
451	    <sect2>
452	      <title>The Translation Table Manager (TTM)</title>
453	      <para>
454		TTM design background and information belongs here.
455	      </para>
456	      <sect3>
457		<title>TTM initialization</title>
458	        <warning><para>This section is outdated.</para></warning>
459	        <para>
460	          Drivers wishing to support TTM must fill out a drm_bo_driver
461	          structure. The structure contains several fields with function
462	          pointers for initializing the TTM, allocating and freeing memory,
463	          waiting for command completion and fence synchronization, and memory
464	          migration. See the radeon_ttm.c file for an example of usage.
465		</para>
466		<para>
467		  The ttm_global_reference structure is made up of several fields:
468		</para>
469		<programlisting>
470		  struct ttm_global_reference {
471		  	enum ttm_global_types global_type;
472		  	size_t size;
473		  	void *object;
474		  	int (*init) (struct ttm_global_reference *);
475		  	void (*release) (struct ttm_global_reference *);
476		  };
477		</programlisting>
478		<para>
479		  There should be one global reference structure for your memory
480		  manager as a whole, and there will be others for each object
481		  created by the memory manager at runtime.  Your global TTM should
482		  have a type of TTM_GLOBAL_TTM_MEM.  The size field for the global
483		  object should be sizeof(struct ttm_mem_global), and the init and
484		  release hooks should point at your driver-specific init and
485		  release routines, which probably eventually call
486		  ttm_mem_global_init and ttm_mem_global_release, respectively.
487		</para>
488		<para>
489		  Once your global TTM accounting structure is set up and initialized
490		  by calling ttm_global_item_ref() on it,
491		  you need to create a buffer object TTM to
492		  provide a pool for buffer object allocation by clients and the
493		  kernel itself.  The type of this object should be TTM_GLOBAL_TTM_BO,
494		  and its size should be sizeof(struct ttm_bo_global).  Again,
495		  driver-specific init and release functions may be provided,
496		  likely eventually calling ttm_bo_global_init() and
497		  ttm_bo_global_release(), respectively.  Also, like the previous
498		  object, ttm_global_item_ref() is used to create an initial reference
499		  count for the TTM, which will call your initialization function.
500		</para>
501	      </sect3>
502	    </sect2>
503	    <sect2 id="drm-gem">
504	      <title>The Graphics Execution Manager (GEM)</title>
505	      <para>
506	        The GEM design approach has resulted in a memory manager that doesn't
507	        provide full coverage of all (or even all common) use cases in its
508	        userspace or kernel API. GEM exposes a set of standard memory-related
509	        operations to userspace and a set of helper functions to drivers, and let
510	        drivers implement hardware-specific operations with their own private API.
511	      </para>
512	      <para>
513	        The GEM userspace API is described in the
514	        <ulink url="http://lwn.net/Articles/283798/"><citetitle>GEM - the Graphics
515	        Execution Manager</citetitle></ulink> article on LWN. While slightly
516	        outdated, the document provides a good overview of the GEM API principles.
517	        Buffer allocation and read and write operations, described as part of the
518	        common GEM API, are currently implemented using driver-specific ioctls.
519	      </para>
520	      <para>
521	        GEM is data-agnostic. It manages abstract buffer objects without knowing
522	        what individual buffers contain. APIs that require knowledge of buffer
523	        contents or purpose, such as buffer allocation or synchronization
524	        primitives, are thus outside of the scope of GEM and must be implemented
525	        using driver-specific ioctls.
526	      </para>
527	      <para>
528		On a fundamental level, GEM involves several operations:
529		<itemizedlist>
530		  <listitem>Memory allocation and freeing</listitem>
531		  <listitem>Command execution</listitem>
532		  <listitem>Aperture management at command execution time</listitem>
533		</itemizedlist>
534		Buffer object allocation is relatively straightforward and largely
535	        provided by Linux's shmem layer, which provides memory to back each
536	        object.
537	      </para>
538	      <para>
539	        Device-specific operations, such as command execution, pinning, buffer
540		read &amp; write, mapping, and domain ownership transfers are left to
541	        driver-specific ioctls.
542	      </para>
543	      <sect3>
544	        <title>GEM Initialization</title>
545	        <para>
546	          Drivers that use GEM must set the DRIVER_GEM bit in the struct
547	          <structname>drm_driver</structname>
548	          <structfield>driver_features</structfield> field. The DRM core will
549	          then automatically initialize the GEM core before calling the
550	          <methodname>load</methodname> operation. Behind the scene, this will
551	          create a DRM Memory Manager object which provides an address space
552	          pool for object allocation.
553	        </para>
554	        <para>
555	          In a KMS configuration, drivers need to allocate and initialize a
556	          command ring buffer following core GEM initialization if required by
557	          the hardware. UMA devices usually have what is called a "stolen"
558	          memory region, which provides space for the initial framebuffer and
559	          large, contiguous memory regions required by the device. This space is
560	          typically not managed by GEM, and must be initialized separately into
561	          its own DRM MM object.
562	        </para>
563	      </sect3>
564	      <sect3>
565	        <title>GEM Objects Creation</title>
566	        <para>
567	          GEM splits creation of GEM objects and allocation of the memory that
568	          backs them in two distinct operations.
569	        </para>
570	        <para>
571	          GEM objects are represented by an instance of struct
572	          <structname>drm_gem_object</structname>. Drivers usually need to extend
573	          GEM objects with private information and thus create a driver-specific
574	          GEM object structure type that embeds an instance of struct
575	          <structname>drm_gem_object</structname>.
576	        </para>
577	        <para>
578	          To create a GEM object, a driver allocates memory for an instance of its
579	          specific GEM object type and initializes the embedded struct
580	          <structname>drm_gem_object</structname> with a call to
581	          <function>drm_gem_object_init</function>. The function takes a pointer to
582	          the DRM device, a pointer to the GEM object and the buffer object size
583	          in bytes.
584	        </para>
585	        <para>
586	          GEM uses shmem to allocate anonymous pageable memory.
587	          <function>drm_gem_object_init</function> will create an shmfs file of
588	          the requested size and store it into the struct
589	          <structname>drm_gem_object</structname> <structfield>filp</structfield>
590	          field. The memory is used as either main storage for the object when the
591	          graphics hardware uses system memory directly or as a backing store
592	          otherwise.
593	        </para>
594	        <para>
595	          Drivers are responsible for the actual physical pages allocation by
596	          calling <function>shmem_read_mapping_page_gfp</function> for each page.
597	          Note that they can decide to allocate pages when initializing the GEM
598	          object, or to delay allocation until the memory is needed (for instance
599	          when a page fault occurs as a result of a userspace memory access or
600	          when the driver needs to start a DMA transfer involving the memory).
601	        </para>
602	        <para>
603	          Anonymous pageable memory allocation is not always desired, for instance
604	          when the hardware requires physically contiguous system memory as is
605	          often the case in embedded devices. Drivers can create GEM objects with
606	          no shmfs backing (called private GEM objects) by initializing them with
607	          a call to <function>drm_gem_private_object_init</function> instead of
608	          <function>drm_gem_object_init</function>. Storage for private GEM
609	          objects must be managed by drivers.
610	        </para>
611	        <para>
612	          Drivers that do not need to extend GEM objects with private information
613	          can call the <function>drm_gem_object_alloc</function> function to
614	          allocate and initialize a struct <structname>drm_gem_object</structname>
615	          instance. The GEM core will call the optional driver
616	          <methodname>gem_init_object</methodname> operation after initializing
617	          the GEM object with <function>drm_gem_object_init</function>.
618	          <synopsis>int (*gem_init_object) (struct drm_gem_object *obj);</synopsis>
619	        </para>
620	        <para>
621	          No alloc-and-init function exists for private GEM objects.
622	        </para>
623	      </sect3>
624	      <sect3>
625	        <title>GEM Objects Lifetime</title>
626	        <para>
627	          All GEM objects are reference-counted by the GEM core. References can be
628	          acquired and release by <function>calling drm_gem_object_reference</function>
629	          and <function>drm_gem_object_unreference</function> respectively. The
630	          caller must hold the <structname>drm_device</structname>
631	          <structfield>struct_mutex</structfield> lock. As a convenience, GEM
632	          provides the <function>drm_gem_object_reference_unlocked</function> and
633	          <function>drm_gem_object_unreference_unlocked</function> functions that
634	          can be called without holding the lock.
635	        </para>
636	        <para>
637	          When the last reference to a GEM object is released the GEM core calls
638	          the <structname>drm_driver</structname>
639	          <methodname>gem_free_object</methodname> operation. That operation is
640	          mandatory for GEM-enabled drivers and must free the GEM object and all
641	          associated resources.
642	        </para>
643	        <para>
644	          <synopsis>void (*gem_free_object) (struct drm_gem_object *obj);</synopsis>
645	          Drivers are responsible for freeing all GEM object resources, including
646	          the resources created by the GEM core. If an mmap offset has been
647	          created for the object (in which case
648	          <structname>drm_gem_object</structname>::<structfield>map_list</structfield>::<structfield>map</structfield>
649	          is not NULL) it must be freed by a call to
650	          <function>drm_gem_free_mmap_offset</function>. The shmfs backing store
651	          must be released by calling <function>drm_gem_object_release</function>
652	          (that function can safely be called if no shmfs backing store has been
653	          created).
654	        </para>
655	      </sect3>
656	      <sect3>
657	        <title>GEM Objects Naming</title>
658	        <para>
659	          Communication between userspace and the kernel refers to GEM objects
660	          using local handles, global names or, more recently, file descriptors.
661	          All of those are 32-bit integer values; the usual Linux kernel limits
662	          apply to the file descriptors.
663	        </para>
664	        <para>
665	          GEM handles are local to a DRM file. Applications get a handle to a GEM
666	          object through a driver-specific ioctl, and can use that handle to refer
667	          to the GEM object in other standard or driver-specific ioctls. Closing a
668	          DRM file handle frees all its GEM handles and dereferences the
669	          associated GEM objects.
670	        </para>
671	        <para>
672	          To create a handle for a GEM object drivers call
673	          <function>drm_gem_handle_create</function>. The function takes a pointer
674	          to the DRM file and the GEM object and returns a locally unique handle.
675	          When the handle is no longer needed drivers delete it with a call to
676	          <function>drm_gem_handle_delete</function>. Finally the GEM object
677	          associated with a handle can be retrieved by a call to
678	          <function>drm_gem_object_lookup</function>.
679	        </para>
680	        <para>
681	          Handles don't take ownership of GEM objects, they only take a reference
682	          to the object that will be dropped when the handle is destroyed. To
683	          avoid leaking GEM objects, drivers must make sure they drop the
684	          reference(s) they own (such as the initial reference taken at object
685	          creation time) as appropriate, without any special consideration for the
686	          handle. For example, in the particular case of combined GEM object and
687	          handle creation in the implementation of the
688	          <methodname>dumb_create</methodname> operation, drivers must drop the
689	          initial reference to the GEM object before returning the handle.
690	        </para>
691	        <para>
692	          GEM names are similar in purpose to handles but are not local to DRM
693	          files. They can be passed between processes to reference a GEM object
694	          globally. Names can't be used directly to refer to objects in the DRM
695	          API, applications must convert handles to names and names to handles
696	          using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
697	          respectively. The conversion is handled by the DRM core without any
698	          driver-specific support.
699	        </para>
700	        <para>
701	          Similar to global names, GEM file descriptors are also used to share GEM
702	          objects across processes. They offer additional security: as file
703	          descriptors must be explicitly sent over UNIX domain sockets to be shared
704	          between applications, they can't be guessed like the globally unique GEM
705	          names.
706	        </para>
707	        <para>
708	          Drivers that support GEM file descriptors, also known as the DRM PRIME
709	          API, must set the DRIVER_PRIME bit in the struct
710	          <structname>drm_driver</structname>
711	          <structfield>driver_features</structfield> field, and implement the
712	          <methodname>prime_handle_to_fd</methodname> and
713	          <methodname>prime_fd_to_handle</methodname> operations.
714	        </para>
715	        <para>
716	          <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
717	                            struct drm_file *file_priv, uint32_t handle,
718	                            uint32_t flags, int *prime_fd);
719	  int (*prime_fd_to_handle)(struct drm_device *dev,
720	                            struct drm_file *file_priv, int prime_fd,
721	                            uint32_t *handle);</synopsis>
722	          Those two operations convert a handle to a PRIME file descriptor and
723	          vice versa. Drivers must use the kernel dma-buf buffer sharing framework
724	          to manage the PRIME file descriptors.
725	        </para>
726	        <para>
727	          While non-GEM drivers must implement the operations themselves, GEM
728	          drivers must use the <function>drm_gem_prime_handle_to_fd</function>
729	          and <function>drm_gem_prime_fd_to_handle</function> helper functions.
730	          Those helpers rely on the driver
731	          <methodname>gem_prime_export</methodname> and
732	          <methodname>gem_prime_import</methodname> operations to create a dma-buf
733	          instance from a GEM object (dma-buf exporter role) and to create a GEM
734	          object from a dma-buf instance (dma-buf importer role).
735	        </para>
736	        <para>
737	          <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
738	                                       struct drm_gem_object *obj,
739	                                       int flags);
740	  struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
741	                                              struct dma_buf *dma_buf);</synopsis>
742	          These two operations are mandatory for GEM drivers that support DRM
743	          PRIME.
744	        </para>
745	        <sect4>
746	          <title>DRM PRIME Helper Functions Reference</title>
747	!Pdrivers/gpu/drm/drm_prime.c PRIME Helpers
748	        </sect4>
749	      </sect3>
750	      <sect3 id="drm-gem-objects-mapping">
751	        <title>GEM Objects Mapping</title>
752	        <para>
753	          Because mapping operations are fairly heavyweight GEM favours
754	          read/write-like access to buffers, implemented through driver-specific
755	          ioctls, over mapping buffers to userspace. However, when random access
756	          to the buffer is needed (to perform software rendering for instance),
757	          direct access to the object can be more efficient.
758	        </para>
759	        <para>
760	          The mmap system call can't be used directly to map GEM objects, as they
761	          don't have their own file handle. Two alternative methods currently
762	          co-exist to map GEM objects to userspace. The first method uses a
763	          driver-specific ioctl to perform the mapping operation, calling
764	          <function>do_mmap</function> under the hood. This is often considered
765	          dubious, seems to be discouraged for new GEM-enabled drivers, and will
766	          thus not be described here.
767	        </para>
768	        <para>
769	          The second method uses the mmap system call on the DRM file handle.
770	          <synopsis>void *mmap(void *addr, size_t length, int prot, int flags, int fd,
771	             off_t offset);</synopsis>
772	          DRM identifies the GEM object to be mapped by a fake offset passed
773	          through the mmap offset argument. Prior to being mapped, a GEM object
774	          must thus be associated with a fake offset. To do so, drivers must call
775	          <function>drm_gem_create_mmap_offset</function> on the object. The
776	          function allocates a fake offset range from a pool and stores the
777	          offset divided by PAGE_SIZE in
778	          <literal>obj-&gt;map_list.hash.key</literal>. Care must be taken not to
779	          call <function>drm_gem_create_mmap_offset</function> if a fake offset
780	          has already been allocated for the object. This can be tested by
781	          <literal>obj-&gt;map_list.map</literal> being non-NULL.
782	        </para>
783	        <para>
784	          Once allocated, the fake offset value
785	          (<literal>obj-&gt;map_list.hash.key &lt;&lt; PAGE_SHIFT</literal>)
786	          must be passed to the application in a driver-specific way and can then
787	          be used as the mmap offset argument.
788	        </para>
789	        <para>
790	          The GEM core provides a helper method <function>drm_gem_mmap</function>
791	          to handle object mapping. The method can be set directly as the mmap
792	          file operation handler. It will look up the GEM object based on the
793	          offset value and set the VMA operations to the
794	          <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
795	          field. Note that <function>drm_gem_mmap</function> doesn't map memory to
796	          userspace, but relies on the driver-provided fault handler to map pages
797	          individually.
798	        </para>
799	        <para>
800	          To use <function>drm_gem_mmap</function>, drivers must fill the struct
801	          <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
802	          field with a pointer to VM operations.
803	        </para>
804	        <para>
805	          <synopsis>struct vm_operations_struct *gem_vm_ops
806	
807	  struct vm_operations_struct {
808	          void (*open)(struct vm_area_struct * area);
809	          void (*close)(struct vm_area_struct * area);
810	          int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
811	  };</synopsis>
812	        </para>
813	        <para>
814	          The <methodname>open</methodname> and <methodname>close</methodname>
815	          operations must update the GEM object reference count. Drivers can use
816	          the <function>drm_gem_vm_open</function> and
817	          <function>drm_gem_vm_close</function> helper functions directly as open
818	          and close handlers.
819	        </para>
820	        <para>
821	          The fault operation handler is responsible for mapping individual pages
822	          to userspace when a page fault occurs. Depending on the memory
823	          allocation scheme, drivers can allocate pages at fault time, or can
824	          decide to allocate memory for the GEM object at the time the object is
825	          created.
826	        </para>
827	        <para>
828	          Drivers that want to map the GEM object upfront instead of handling page
829	          faults can implement their own mmap file operation handler.
830	        </para>
831	      </sect3>
832	      <sect3>
833	        <title>Dumb GEM Objects</title>
834	        <para>
835	          The GEM API doesn't standardize GEM objects creation and leaves it to
836	          driver-specific ioctls. While not an issue for full-fledged graphics
837	          stacks that include device-specific userspace components (in libdrm for
838	          instance), this limit makes DRM-based early boot graphics unnecessarily
839	          complex.
840	        </para>
841	        <para>
842	          Dumb GEM objects partly alleviate the problem by providing a standard
843	          API to create dumb buffers suitable for scanout, which can then be used
844	          to create KMS frame buffers.
845	        </para>
846	        <para>
847	          To support dumb GEM objects drivers must implement the
848	          <methodname>dumb_create</methodname>,
849	          <methodname>dumb_destroy</methodname> and
850	          <methodname>dumb_map_offset</methodname> operations.
851	        </para>
852	        <itemizedlist>
853	          <listitem>
854	            <synopsis>int (*dumb_create)(struct drm_file *file_priv, struct drm_device *dev,
855	                     struct drm_mode_create_dumb *args);</synopsis>
856	            <para>
857	              The <methodname>dumb_create</methodname> operation creates a GEM
858	              object suitable for scanout based on the width, height and depth
859	              from the struct <structname>drm_mode_create_dumb</structname>
860	              argument. It fills the argument's <structfield>handle</structfield>,
861	              <structfield>pitch</structfield> and <structfield>size</structfield>
862	              fields with a handle for the newly created GEM object and its line
863	              pitch and size in bytes.
864	            </para>
865	          </listitem>
866	          <listitem>
867	            <synopsis>int (*dumb_destroy)(struct drm_file *file_priv, struct drm_device *dev,
868	                      uint32_t handle);</synopsis>
869	            <para>
870	              The <methodname>dumb_destroy</methodname> operation destroys a dumb
871	              GEM object created by <methodname>dumb_create</methodname>.
872	            </para>
873	          </listitem>
874	          <listitem>
875	            <synopsis>int (*dumb_map_offset)(struct drm_file *file_priv, struct drm_device *dev,
876	                         uint32_t handle, uint64_t *offset);</synopsis>
877	            <para>
878	              The <methodname>dumb_map_offset</methodname> operation associates an
879	              mmap fake offset with the GEM object given by the handle and returns
880	              it. Drivers must use the
881	              <function>drm_gem_create_mmap_offset</function> function to
882	              associate the fake offset as described in
883	              <xref linkend="drm-gem-objects-mapping"/>.
884	            </para>
885	          </listitem>
886	        </itemizedlist>
887	      </sect3>
888	      <sect3>
889	        <title>Memory Coherency</title>
890	        <para>
891	          When mapped to the device or used in a command buffer, backing pages
892	          for an object are flushed to memory and marked write combined so as to
893	          be coherent with the GPU. Likewise, if the CPU accesses an object
894	          after the GPU has finished rendering to the object, then the object
895	          must be made coherent with the CPU's view of memory, usually involving
896	          GPU cache flushing of various kinds. This core CPU&lt;-&gt;GPU
897	          coherency management is provided by a device-specific ioctl, which
898	          evaluates an object's current domain and performs any necessary
899	          flushing or synchronization to put the object into the desired
900	          coherency domain (note that the object may be busy, i.e. an active
901	          render target; in that case, setting the domain blocks the client and
902	          waits for rendering to complete before performing any necessary
903	          flushing operations).
904	        </para>
905	      </sect3>
906	      <sect3>
907	        <title>Command Execution</title>
908	        <para>
909		  Perhaps the most important GEM function for GPU devices is providing a
910	          command execution interface to clients. Client programs construct
911	          command buffers containing references to previously allocated memory
912	          objects, and then submit them to GEM. At that point, GEM takes care to
913	          bind all the objects into the GTT, execute the buffer, and provide
914	          necessary synchronization between clients accessing the same buffers.
915	          This often involves evicting some objects from the GTT and re-binding
916	          others (a fairly expensive operation), and providing relocation
917	          support which hides fixed GTT offsets from clients. Clients must take
918	          care not to submit command buffers that reference more objects than
919	          can fit in the GTT; otherwise, GEM will reject them and no rendering
920	          will occur. Similarly, if several objects in the buffer require fence
921	          registers to be allocated for correct rendering (e.g. 2D blits on
922	          pre-965 chips), care must be taken not to require more fence registers
923	          than are available to the client. Such resource management should be
924	          abstracted from the client in libdrm.
925	        </para>
926	      </sect3>
927	    </sect2>
928	  </sect1>
929	
930	  <!-- Internals: mode setting -->
931	
932	  <sect1 id="drm-mode-setting">
933	    <title>Mode Setting</title>
934	    <para>
935	      Drivers must initialize the mode setting core by calling
936	      <function>drm_mode_config_init</function> on the DRM device. The function
937	      initializes the <structname>drm_device</structname>
938	      <structfield>mode_config</structfield> field and never fails. Once done,
939	      mode configuration must be setup by initializing the following fields.
940	    </para>
941	    <itemizedlist>
942	      <listitem>
943	        <synopsis>int min_width, min_height;
944	int max_width, max_height;</synopsis>
945	        <para>
946		  Minimum and maximum width and height of the frame buffers in pixel
947		  units.
948		</para>
949	      </listitem>
950	      <listitem>
951	        <synopsis>struct drm_mode_config_funcs *funcs;</synopsis>
952		<para>Mode setting functions.</para>
953	      </listitem>
954	    </itemizedlist>
955	    <sect2>
956	      <title>Frame Buffer Creation</title>
957	      <synopsis>struct drm_framebuffer *(*fb_create)(struct drm_device *dev,
958					     struct drm_file *file_priv,
959					     struct drm_mode_fb_cmd2 *mode_cmd);</synopsis>
960	      <para>
961	        Frame buffers are abstract memory objects that provide a source of
962	        pixels to scanout to a CRTC. Applications explicitly request the
963	        creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and
964	        receive an opaque handle that can be passed to the KMS CRTC control,
965	        plane configuration and page flip functions.
966	      </para>
967	      <para>
968	        Frame buffers rely on the underneath memory manager for low-level memory
969	        operations. When creating a frame buffer applications pass a memory
970	        handle (or a list of memory handles for multi-planar formats) through
971	        the <parameter>drm_mode_fb_cmd2</parameter> argument. This document
972	        assumes that the driver uses GEM, those handles thus reference GEM
973	        objects.
974	      </para>
975	      <para>
976	        Drivers must first validate the requested frame buffer parameters passed
977	        through the mode_cmd argument. In particular this is where invalid
978	        sizes, pixel formats or pitches can be caught.
979	      </para>
980	      <para>
981	        If the parameters are deemed valid, drivers then create, initialize and
982	        return an instance of struct <structname>drm_framebuffer</structname>.
983	        If desired the instance can be embedded in a larger driver-specific
984		structure. Drivers must fill its <structfield>width</structfield>,
985		<structfield>height</structfield>, <structfield>pitches</structfield>,
986	        <structfield>offsets</structfield>, <structfield>depth</structfield>,
987	        <structfield>bits_per_pixel</structfield> and
988	        <structfield>pixel_format</structfield> fields from the values passed
989	        through the <parameter>drm_mode_fb_cmd2</parameter> argument. They
990	        should call the <function>drm_helper_mode_fill_fb_struct</function>
991	        helper function to do so.
992	      </para>
993	
994	      <para>
995		The initailization of the new framebuffer instance is finalized with a
996		call to <function>drm_framebuffer_init</function> which takes a pointer
997		to DRM frame buffer operations (struct
998		<structname>drm_framebuffer_funcs</structname>). Note that this function
999		publishes the framebuffer and so from this point on it can be accessed
1000		concurrently from other threads. Hence it must be the last step in the
1001		driver's framebuffer initialization sequence. Frame buffer operations
1002		are
1003	        <itemizedlist>
1004	          <listitem>
1005	            <synopsis>int (*create_handle)(struct drm_framebuffer *fb,
1006			     struct drm_file *file_priv, unsigned int *handle);</synopsis>
1007	            <para>
1008	              Create a handle to the frame buffer underlying memory object. If
1009	              the frame buffer uses a multi-plane format, the handle will
1010	              reference the memory object associated with the first plane.
1011	            </para>
1012	            <para>
1013	              Drivers call <function>drm_gem_handle_create</function> to create
1014	              the handle.
1015	            </para>
1016	          </listitem>
1017	          <listitem>
1018	            <synopsis>void (*destroy)(struct drm_framebuffer *framebuffer);</synopsis>
1019	            <para>
1020	              Destroy the frame buffer object and frees all associated
1021	              resources. Drivers must call
1022	              <function>drm_framebuffer_cleanup</function> to free resources
1023	              allocated by the DRM core for the frame buffer object, and must
1024	              make sure to unreference all memory objects associated with the
1025	              frame buffer. Handles created by the
1026	              <methodname>create_handle</methodname> operation are released by
1027	              the DRM core.
1028	            </para>
1029	          </listitem>
1030	          <listitem>
1031	            <synopsis>int (*dirty)(struct drm_framebuffer *framebuffer,
1032		     struct drm_file *file_priv, unsigned flags, unsigned color,
1033		     struct drm_clip_rect *clips, unsigned num_clips);</synopsis>
1034	            <para>
1035	              This optional operation notifies the driver that a region of the
1036	              frame buffer has changed in response to a DRM_IOCTL_MODE_DIRTYFB
1037	              ioctl call.
1038	            </para>
1039	          </listitem>
1040	        </itemizedlist>
1041	      </para>
1042	      <para>
1043		The lifetime of a drm framebuffer is controlled with a reference count,
1044		drivers can grab additional references with
1045		<function>drm_framebuffer_reference</function> </para> and drop them
1046		again with <function>drm_framebuffer_unreference</function>. For
1047		driver-private framebuffers for which the last reference is never
1048		dropped (e.g. for the fbdev framebuffer when the struct
1049		<structname>drm_framebuffer</structname> is embedded into the fbdev
1050		helper struct) drivers can manually clean up a framebuffer at module
1051		unload time with
1052		<function>drm_framebuffer_unregister_private</function>.
1053	    </sect2>
1054	    <sect2>
1055	      <title>Output Polling</title>
1056	      <synopsis>void (*output_poll_changed)(struct drm_device *dev);</synopsis>
1057	      <para>
1058	        This operation notifies the driver that the status of one or more
1059	        connectors has changed. Drivers that use the fb helper can just call the
1060	        <function>drm_fb_helper_hotplug_event</function> function to handle this
1061	        operation.
1062	      </para>
1063	    </sect2>
1064	    <sect2>
1065	      <title>Locking</title>
1066	      <para>
1067	        Beside some lookup structures with their own locking (which is hidden
1068		behind the interface functions) most of the modeset state is protected
1069		by the <code>dev-&lt;mode_config.lock</code> mutex and additionally
1070		per-crtc locks to allow cursor updates, pageflips and similar operations
1071		to occur concurrently with background tasks like output detection.
1072		Operations which cross domains like a full modeset always grab all
1073		locks. Drivers there need to protect resources shared between crtcs with
1074		additional locking. They also need to be careful to always grab the
1075		relevant crtc locks if a modset functions touches crtc state, e.g. for
1076		load detection (which does only grab the <code>mode_config.lock</code>
1077		to allow concurrent screen updates on live crtcs).
1078	      </para>
1079	    </sect2>
1080	  </sect1>
1081	
1082	  <!-- Internals: kms initialization and cleanup -->
1083	
1084	  <sect1 id="drm-kms-init">
1085	    <title>KMS Initialization and Cleanup</title>
1086	    <para>
1087	      A KMS device is abstracted and exposed as a set of planes, CRTCs, encoders
1088	      and connectors. KMS drivers must thus create and initialize all those
1089	      objects at load time after initializing mode setting.
1090	    </para>
1091	    <sect2>
1092	      <title>CRTCs (struct <structname>drm_crtc</structname>)</title>
1093	      <para>
1094	        A CRTC is an abstraction representing a part of the chip that contains a
1095		pointer to a scanout buffer. Therefore, the number of CRTCs available
1096		determines how many independent scanout buffers can be active at any
1097		given time. The CRTC structure contains several fields to support this:
1098		a pointer to some video memory (abstracted as a frame buffer object), a
1099		display mode, and an (x, y) offset into the video memory to support
1100		panning or configurations where one piece of video memory spans multiple
1101		CRTCs.
1102	      </para>
1103	      <sect3>
1104	        <title>CRTC Initialization</title>
1105	        <para>
1106	          A KMS device must create and register at least one struct
1107	          <structname>drm_crtc</structname> instance. The instance is allocated
1108	          and zeroed by the driver, possibly as part of a larger structure, and
1109	          registered with a call to <function>drm_crtc_init</function> with a
1110	          pointer to CRTC functions.
1111	        </para>
1112	      </sect3>
1113	      <sect3>
1114	        <title>CRTC Operations</title>
1115	        <sect4>
1116	          <title>Set Configuration</title>
1117	          <synopsis>int (*set_config)(struct drm_mode_set *set);</synopsis>
1118	          <para>
1119	            Apply a new CRTC configuration to the device. The configuration
1120	            specifies a CRTC, a frame buffer to scan out from, a (x,y) position in
1121	            the frame buffer, a display mode and an array of connectors to drive
1122	            with the CRTC if possible.
1123	          </para>
1124	          <para>
1125	            If the frame buffer specified in the configuration is NULL, the driver
1126	            must detach all encoders connected to the CRTC and all connectors
1127	            attached to those encoders and disable them.
1128	          </para>
1129	          <para>
1130	            This operation is called with the mode config lock held.
1131	          </para>
1132	          <note><para>
1133	            FIXME: How should set_config interact with DPMS? If the CRTC is
1134	            suspended, should it be resumed?
1135	          </para></note>
1136	        </sect4>
1137	        <sect4>
1138	          <title>Page Flipping</title>
1139	          <synopsis>int (*page_flip)(struct drm_crtc *crtc, struct drm_framebuffer *fb,
1140	                   struct drm_pending_vblank_event *event);</synopsis>
1141	          <para>
1142	            Schedule a page flip to the given frame buffer for the CRTC. This
1143	            operation is called with the mode config mutex held.
1144	          </para>
1145	          <para>
1146	            Page flipping is a synchronization mechanism that replaces the frame
1147	            buffer being scanned out by the CRTC with a new frame buffer during
1148	            vertical blanking, avoiding tearing. When an application requests a page
1149	            flip the DRM core verifies that the new frame buffer is large enough to
1150	            be scanned out by  the CRTC in the currently configured mode and then
1151	            calls the CRTC <methodname>page_flip</methodname> operation with a
1152	            pointer to the new frame buffer.
1153	          </para>
1154	          <para>
1155	            The <methodname>page_flip</methodname> operation schedules a page flip.
1156	            Once any pending rendering targeting the new frame buffer has
1157	            completed, the CRTC will be reprogrammed to display that frame buffer
1158	            after the next vertical refresh. The operation must return immediately
1159	            without waiting for rendering or page flip to complete and must block
1160	            any new rendering to the frame buffer until the page flip completes.
1161	          </para>
1162	          <para>
1163	            If a page flip can be successfully scheduled the driver must set the
1164	            <code>drm_crtc-&lt;fb</code> field to the new framebuffer pointed to
1165	            by <code>fb</code>. This is important so that the reference counting
1166	            on framebuffers stays balanced.
1167	          </para>
1168	          <para>
1169	            If a page flip is already pending, the
1170	            <methodname>page_flip</methodname> operation must return
1171	            -<errorname>EBUSY</errorname>.
1172	          </para>
1173	          <para>
1174	            To synchronize page flip to vertical blanking the driver will likely
1175	            need to enable vertical blanking interrupts. It should call
1176	            <function>drm_vblank_get</function> for that purpose, and call
1177	            <function>drm_vblank_put</function> after the page flip completes.
1178	          </para>
1179	          <para>
1180	            If the application has requested to be notified when page flip completes
1181	            the <methodname>page_flip</methodname> operation will be called with a
1182	            non-NULL <parameter>event</parameter> argument pointing to a
1183	            <structname>drm_pending_vblank_event</structname> instance. Upon page
1184	            flip completion the driver must call <methodname>drm_send_vblank_event</methodname>
1185	            to fill in the event and send to wake up any waiting processes.
1186	            This can be performed with
1187	            <programlisting><![CDATA[
1188	            spin_lock_irqsave(&dev->event_lock, flags);
1189	            ...
1190	            drm_send_vblank_event(dev, pipe, event);
1191	            spin_unlock_irqrestore(&dev->event_lock, flags);
1192	            ]]></programlisting>
1193	          </para>
1194	          <note><para>
1195	            FIXME: Could drivers that don't need to wait for rendering to complete
1196	            just add the event to <literal>dev-&gt;vblank_event_list</literal> and
1197	            let the DRM core handle everything, as for "normal" vertical blanking
1198	            events?
1199	          </para></note>
1200	          <para>
1201	            While waiting for the page flip to complete, the
1202	            <literal>event-&gt;base.link</literal> list head can be used freely by
1203	            the driver to store the pending event in a driver-specific list.
1204	          </para>
1205	          <para>
1206	            If the file handle is closed before the event is signaled, drivers must
1207	            take care to destroy the event in their
1208	            <methodname>preclose</methodname> operation (and, if needed, call
1209	            <function>drm_vblank_put</function>).
1210	          </para>
1211	        </sect4>
1212	        <sect4>
1213	          <title>Miscellaneous</title>
1214	          <itemizedlist>
1215	            <listitem>
1216	              <synopsis>void (*set_property)(struct drm_crtc *crtc,
1217	                     struct drm_property *property, uint64_t value);</synopsis>
1218	              <para>
1219	                Set the value of the given CRTC property to
1220	                <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/>
1221	                for more information about properties.
1222	              </para>
1223	            </listitem>
1224	            <listitem>
1225	              <synopsis>void (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b,
1226	                        uint32_t start, uint32_t size);</synopsis>
1227	              <para>
1228	                Apply a gamma table to the device. The operation is optional.
1229	              </para>
1230	            </listitem>
1231	            <listitem>
1232	              <synopsis>void (*destroy)(struct drm_crtc *crtc);</synopsis>
1233	              <para>
1234	                Destroy the CRTC when not needed anymore. See
1235	                <xref linkend="drm-kms-init"/>.
1236	              </para>
1237	            </listitem>
1238	          </itemizedlist>
1239	        </sect4>
1240	      </sect3>
1241	    </sect2>
1242	    <sect2>
1243	      <title>Planes (struct <structname>drm_plane</structname>)</title>
1244	      <para>
1245	        A plane represents an image source that can be blended with or overlayed
1246		on top of a CRTC during the scanout process. Planes are associated with
1247		a frame buffer to crop a portion of the image memory (source) and
1248		optionally scale it to a destination size. The result is then blended
1249		with or overlayed on top of a CRTC.
1250	      </para>
1251	      <sect3>
1252	        <title>Plane Initialization</title>
1253	        <para>
1254	          Planes are optional. To create a plane, a KMS drivers allocates and
1255	          zeroes an instances of struct <structname>drm_plane</structname>
1256	          (possibly as part of a larger structure) and registers it with a call
1257	          to <function>drm_plane_init</function>. The function takes a bitmask
1258	          of the CRTCs that can be associated with the plane, a pointer to the
1259	          plane functions and a list of format supported formats.
1260	        </para>
1261	      </sect3>
1262	      <sect3>
1263	        <title>Plane Operations</title>
1264	        <itemizedlist>
1265	          <listitem>
1266	            <synopsis>int (*update_plane)(struct drm_plane *plane, struct drm_crtc *crtc,
1267	                        struct drm_framebuffer *fb, int crtc_x, int crtc_y,
1268	                        unsigned int crtc_w, unsigned int crtc_h,
1269	                        uint32_t src_x, uint32_t src_y,
1270	                        uint32_t src_w, uint32_t src_h);</synopsis>
1271	            <para>
1272	              Enable and configure the plane to use the given CRTC and frame buffer.
1273	            </para>
1274	            <para>
1275	              The source rectangle in frame buffer memory coordinates is given by
1276	              the <parameter>src_x</parameter>, <parameter>src_y</parameter>,
1277	              <parameter>src_w</parameter> and <parameter>src_h</parameter>
1278	              parameters (as 16.16 fixed point values). Devices that don't support
1279	              subpixel plane coordinates can ignore the fractional part.
1280	            </para>
1281	            <para>
1282	              The destination rectangle in CRTC coordinates is given by the
1283	              <parameter>crtc_x</parameter>, <parameter>crtc_y</parameter>,
1284	              <parameter>crtc_w</parameter> and <parameter>crtc_h</parameter>
1285	              parameters (as integer values). Devices scale the source rectangle to
1286	              the destination rectangle. If scaling is not supported, and the source
1287	              rectangle size doesn't match the destination rectangle size, the
1288	              driver must return a -<errorname>EINVAL</errorname> error.
1289	            </para>
1290	          </listitem>
1291	          <listitem>
1292	            <synopsis>int (*disable_plane)(struct drm_plane *plane);</synopsis>
1293	            <para>
1294	              Disable the plane. The DRM core calls this method in response to a
1295	              DRM_IOCTL_MODE_SETPLANE ioctl call with the frame buffer ID set to 0.
1296	              Disabled planes must not be processed by the CRTC.
1297	            </para>
1298	          </listitem>
1299	          <listitem>
1300	            <synopsis>void (*destroy)(struct drm_plane *plane);</synopsis>
1301	            <para>
1302	              Destroy the plane when not needed anymore. See
1303	              <xref linkend="drm-kms-init"/>.
1304	            </para>
1305	          </listitem>
1306	        </itemizedlist>
1307	      </sect3>
1308	    </sect2>
1309	    <sect2>
1310	      <title>Encoders (struct <structname>drm_encoder</structname>)</title>
1311	      <para>
1312	        An encoder takes pixel data from a CRTC and converts it to a format
1313		suitable for any attached connectors. On some devices, it may be
1314		possible to have a CRTC send data to more than one encoder. In that
1315		case, both encoders would receive data from the same scanout buffer,
1316		resulting in a "cloned" display configuration across the connectors
1317		attached to each encoder.
1318	      </para>
1319	      <sect3>
1320	        <title>Encoder Initialization</title>
1321	        <para>
1322	          As for CRTCs, a KMS driver must create, initialize and register at
1323	          least one struct <structname>drm_encoder</structname> instance. The
1324	          instance is allocated and zeroed by the driver, possibly as part of a
1325	          larger structure.
1326	        </para>
1327	        <para>
1328	          Drivers must initialize the struct <structname>drm_encoder</structname>
1329	          <structfield>possible_crtcs</structfield> and
1330	          <structfield>possible_clones</structfield> fields before registering the
1331	          encoder. Both fields are bitmasks of respectively the CRTCs that the
1332	          encoder can be connected to, and sibling encoders candidate for cloning.
1333	        </para>
1334	        <para>
1335	          After being initialized, the encoder must be registered with a call to
1336	          <function>drm_encoder_init</function>. The function takes a pointer to
1337	          the encoder functions and an encoder type. Supported types are
1338	          <itemizedlist>
1339	            <listitem>
1340	              DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
1341	              </listitem>
1342	            <listitem>
1343	              DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
1344	            </listitem>
1345	            <listitem>
1346	              DRM_MODE_ENCODER_LVDS for display panels
1347	            </listitem>
1348	            <listitem>
1349	              DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component,
1350	              SCART)
1351	            </listitem>
1352	            <listitem>
1353	              DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
1354	            </listitem>
1355	          </itemizedlist>
1356	        </para>
1357	        <para>
1358	          Encoders must be attached to a CRTC to be used. DRM drivers leave
1359	          encoders unattached at initialization time. Applications (or the fbdev
1360	          compatibility layer when implemented) are responsible for attaching the
1361	          encoders they want to use to a CRTC.
1362	        </para>
1363	      </sect3>
1364	      <sect3>
1365	        <title>Encoder Operations</title>
1366	        <itemizedlist>
1367	          <listitem>
1368	            <synopsis>void (*destroy)(struct drm_encoder *encoder);</synopsis>
1369	            <para>
1370	              Called to destroy the encoder when not needed anymore. See
1371	              <xref linkend="drm-kms-init"/>.
1372	            </para>
1373	          </listitem>
1374	          <listitem>
1375	            <synopsis>void (*set_property)(struct drm_plane *plane,
1376	                     struct drm_property *property, uint64_t value);</synopsis>
1377	            <para>
1378	              Set the value of the given plane property to
1379	              <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/>
1380	              for more information about properties.
1381	            </para>
1382	          </listitem>
1383	        </itemizedlist>
1384	      </sect3>
1385	    </sect2>
1386	    <sect2>
1387	      <title>Connectors (struct <structname>drm_connector</structname>)</title>
1388	      <para>
1389	        A connector is the final destination for pixel data on a device, and
1390		usually connects directly to an external display device like a monitor
1391		or laptop panel. A connector can only be attached to one encoder at a
1392		time. The connector is also the structure where information about the
1393		attached display is kept, so it contains fields for display data, EDID
1394		data, DPMS &amp; connection status, and information about modes
1395		supported on the attached displays.
1396	      </para>
1397	      <sect3>
1398	        <title>Connector Initialization</title>
1399	        <para>
1400	          Finally a KMS driver must create, initialize, register and attach at
1401	          least one struct <structname>drm_connector</structname> instance. The
1402	          instance is created as other KMS objects and initialized by setting the
1403	          following fields.
1404	        </para>
1405	        <variablelist>
1406	          <varlistentry>
1407	            <term><structfield>interlace_allowed</structfield></term>
1408	            <listitem><para>
1409	              Whether the connector can handle interlaced modes.
1410	            </para></listitem>
1411	          </varlistentry>
1412	          <varlistentry>
1413	            <term><structfield>doublescan_allowed</structfield></term>
1414	            <listitem><para>
1415	              Whether the connector can handle doublescan.
1416	            </para></listitem>
1417	          </varlistentry>
1418	          <varlistentry>
1419	            <term><structfield>display_info
1420	            </structfield></term>
1421	            <listitem><para>
1422	              Display information is filled from EDID information when a display
1423	              is detected. For non hot-pluggable displays such as flat panels in
1424	              embedded systems, the driver should initialize the
1425	              <structfield>display_info</structfield>.<structfield>width_mm</structfield>
1426	              and
1427	              <structfield>display_info</structfield>.<structfield>height_mm</structfield>
1428	              fields with the physical size of the display.
1429	            </para></listitem>
1430	          </varlistentry>
1431	          <varlistentry>
1432	            <term id="drm-kms-connector-polled"><structfield>polled</structfield></term>
1433	            <listitem><para>
1434	              Connector polling mode, a combination of
1435	              <variablelist>
1436	                <varlistentry>
1437	                  <term>DRM_CONNECTOR_POLL_HPD</term>
1438	                  <listitem><para>
1439	                    The connector generates hotplug events and doesn't need to be
1440	                    periodically polled. The CONNECT and DISCONNECT flags must not
1441	                    be set together with the HPD flag.
1442	                  </para></listitem>
1443	                </varlistentry>
1444	                <varlistentry>
1445	                  <term>DRM_CONNECTOR_POLL_CONNECT</term>
1446	                  <listitem><para>
1447	                    Periodically poll the connector for connection.
1448	                  </para></listitem>
1449	                </varlistentry>
1450	                <varlistentry>
1451	                  <term>DRM_CONNECTOR_POLL_DISCONNECT</term>
1452	                  <listitem><para>
1453	                    Periodically poll the connector for disconnection.
1454	                  </para></listitem>
1455	                </varlistentry>
1456	              </variablelist>
1457	              Set to 0 for connectors that don't support connection status
1458	              discovery.
1459	            </para></listitem>
1460	          </varlistentry>
1461	        </variablelist>
1462	        <para>
1463	          The connector is then registered with a call to
1464	          <function>drm_connector_init</function> with a pointer to the connector
1465	          functions and a connector type, and exposed through sysfs with a call to
1466	          <function>drm_sysfs_connector_add</function>.
1467	        </para>
1468	        <para>
1469	          Supported connector types are
1470	          <itemizedlist>
1471	            <listitem>DRM_MODE_CONNECTOR_VGA</listitem>
1472	            <listitem>DRM_MODE_CONNECTOR_DVII</listitem>
1473	            <listitem>DRM_MODE_CONNECTOR_DVID</listitem>
1474	            <listitem>DRM_MODE_CONNECTOR_DVIA</listitem>
1475	            <listitem>DRM_MODE_CONNECTOR_Composite</listitem>
1476	            <listitem>DRM_MODE_CONNECTOR_SVIDEO</listitem>
1477	            <listitem>DRM_MODE_CONNECTOR_LVDS</listitem>
1478	            <listitem>DRM_MODE_CONNECTOR_Component</listitem>
1479	            <listitem>DRM_MODE_CONNECTOR_9PinDIN</listitem>
1480	            <listitem>DRM_MODE_CONNECTOR_DisplayPort</listitem>
1481	            <listitem>DRM_MODE_CONNECTOR_HDMIA</listitem>
1482	            <listitem>DRM_MODE_CONNECTOR_HDMIB</listitem>
1483	            <listitem>DRM_MODE_CONNECTOR_TV</listitem>
1484	            <listitem>DRM_MODE_CONNECTOR_eDP</listitem>
1485	            <listitem>DRM_MODE_CONNECTOR_VIRTUAL</listitem>
1486	          </itemizedlist>
1487	        </para>
1488	        <para>
1489	          Connectors must be attached to an encoder to be used. For devices that
1490	          map connectors to encoders 1:1, the connector should be attached at
1491	          initialization time with a call to
1492	          <function>drm_mode_connector_attach_encoder</function>. The driver must
1493	          also set the <structname>drm_connector</structname>
1494	          <structfield>encoder</structfield> field to point to the attached
1495	          encoder.
1496	        </para>
1497	        <para>
1498	          Finally, drivers must initialize the connectors state change detection
1499	          with a call to <function>drm_kms_helper_poll_init</function>. If at
1500	          least one connector is pollable but can't generate hotplug interrupts
1501	          (indicated by the DRM_CONNECTOR_POLL_CONNECT and
1502	          DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will
1503	          automatically be queued to periodically poll for changes. Connectors
1504	          that can generate hotplug interrupts must be marked with the
1505	          DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must
1506	          call <function>drm_helper_hpd_irq_event</function>. The function will
1507	          queue a delayed work to check the state of all connectors, but no
1508	          periodic polling will be done.
1509	        </para>
1510	      </sect3>
1511	      <sect3>
1512	        <title>Connector Operations</title>
1513	        <note><para>
1514	          Unless otherwise state, all operations are mandatory.
1515	        </para></note>
1516	        <sect4>
1517	          <title>DPMS</title>
1518	          <synopsis>void (*dpms)(struct drm_connector *connector, int mode);</synopsis>
1519	          <para>
1520	            The DPMS operation sets the power state of a connector. The mode
1521	            argument is one of
1522	            <itemizedlist>
1523	              <listitem><para>DRM_MODE_DPMS_ON</para></listitem>
1524	              <listitem><para>DRM_MODE_DPMS_STANDBY</para></listitem>
1525	              <listitem><para>DRM_MODE_DPMS_SUSPEND</para></listitem>
1526	              <listitem><para>DRM_MODE_DPMS_OFF</para></listitem>
1527	            </itemizedlist>
1528	          </para>
1529	          <para>
1530	            In all but DPMS_ON mode the encoder to which the connector is attached
1531	            should put the display in low-power mode by driving its signals
1532	            appropriately. If more than one connector is attached to the encoder
1533	            care should be taken not to change the power state of other displays as
1534	            a side effect. Low-power mode should be propagated to the encoders and
1535	            CRTCs when all related connectors are put in low-power mode.
1536	          </para>
1537	        </sect4>
1538	        <sect4>
1539	          <title>Modes</title>
1540	          <synopsis>int (*fill_modes)(struct drm_connector *connector, uint32_t max_width,
1541	                      uint32_t max_height);</synopsis>
1542	          <para>
1543	            Fill the mode list with all supported modes for the connector. If the
1544	            <parameter>max_width</parameter> and <parameter>max_height</parameter>
1545	            arguments are non-zero, the implementation must ignore all modes wider
1546	            than <parameter>max_width</parameter> or higher than
1547	            <parameter>max_height</parameter>.
1548	          </para>
1549	          <para>
1550	            The connector must also fill in this operation its
1551	            <structfield>display_info</structfield>
1552	            <structfield>width_mm</structfield> and
1553	            <structfield>height_mm</structfield> fields with the connected display
1554	            physical size in millimeters. The fields should be set to 0 if the value
1555	            isn't known or is not applicable (for instance for projector devices).
1556	          </para>
1557	        </sect4>
1558	        <sect4>
1559	          <title>Connection Status</title>
1560	          <para>
1561	            The connection status is updated through polling or hotplug events when
1562	            supported (see <xref linkend="drm-kms-connector-polled"/>). The status
1563	            value is reported to userspace through ioctls and must not be used
1564	            inside the driver, as it only gets initialized by a call to
1565	            <function>drm_mode_getconnector</function> from userspace.
1566	          </para>
1567	          <synopsis>enum drm_connector_status (*detect)(struct drm_connector *connector,
1568	                                        bool force);</synopsis>
1569	          <para>
1570	            Check to see if anything is attached to the connector. The
1571	            <parameter>force</parameter> parameter is set to false whilst polling or
1572	            to true when checking the connector due to user request.
1573	            <parameter>force</parameter> can be used by the driver to avoid
1574	            expensive, destructive operations during automated probing.
1575	          </para>
1576	          <para>
1577	            Return connector_status_connected if something is connected to the
1578	            connector, connector_status_disconnected if nothing is connected and
1579	            connector_status_unknown if the connection state isn't known.
1580	          </para>
1581	          <para>
1582	            Drivers should only return connector_status_connected if the connection
1583	            status has really been probed as connected. Connectors that can't detect
1584	            the connection status, or failed connection status probes, should return
1585	            connector_status_unknown.
1586	          </para>
1587	        </sect4>
1588	        <sect4>
1589	          <title>Miscellaneous</title>
1590	          <itemizedlist>
1591	            <listitem>
1592	              <synopsis>void (*set_property)(struct drm_connector *connector,
1593	                     struct drm_property *property, uint64_t value);</synopsis>
1594	              <para>
1595	                Set the value of the given connector property to
1596	                <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/>
1597	                for more information about properties.
1598	              </para>
1599	            </listitem>
1600	            <listitem>
1601	              <synopsis>void (*destroy)(struct drm_connector *connector);</synopsis>
1602	              <para>
1603	                Destroy the connector when not needed anymore. See
1604	                <xref linkend="drm-kms-init"/>.
1605	              </para>
1606	            </listitem>
1607	          </itemizedlist>
1608	        </sect4>
1609	      </sect3>
1610	    </sect2>
1611	    <sect2>
1612	      <title>Cleanup</title>
1613	      <para>
1614	        The DRM core manages its objects' lifetime. When an object is not needed
1615		anymore the core calls its destroy function, which must clean up and
1616		free every resource allocated for the object. Every
1617		<function>drm_*_init</function> call must be matched with a
1618		corresponding <function>drm_*_cleanup</function> call to cleanup CRTCs
1619		(<function>drm_crtc_cleanup</function>), planes
1620		(<function>drm_plane_cleanup</function>), encoders
1621		(<function>drm_encoder_cleanup</function>) and connectors
1622		(<function>drm_connector_cleanup</function>). Furthermore, connectors
1623		that have been added to sysfs must be removed by a call to
1624		<function>drm_sysfs_connector_remove</function> before calling
1625		<function>drm_connector_cleanup</function>.
1626	      </para>
1627	      <para>
1628	        Connectors state change detection must be cleanup up with a call to
1629		<function>drm_kms_helper_poll_fini</function>.
1630	      </para>
1631	    </sect2>
1632	    <sect2>
1633	      <title>Output discovery and initialization example</title>
1634	      <programlisting><![CDATA[
1635	void intel_crt_init(struct drm_device *dev)
1636	{
1637		struct drm_connector *connector;
1638		struct intel_output *intel_output;
1639	
1640		intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
1641		if (!intel_output)
1642			return;
1643	
1644		connector = &intel_output->base;
1645		drm_connector_init(dev, &intel_output->base,
1646				   &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
1647	
1648		drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
1649				 DRM_MODE_ENCODER_DAC);
1650	
1651		drm_mode_connector_attach_encoder(&intel_output->base,
1652						  &intel_output->enc);
1653	
1654		/* Set up the DDC bus. */
1655		intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
1656		if (!intel_output->ddc_bus) {
1657			dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
1658				   "failed.\n");
1659			return;
1660		}
1661	
1662		intel_output->type = INTEL_OUTPUT_ANALOG;
1663		connector->interlace_allowed = 0;
1664		connector->doublescan_allowed = 0;
1665	
1666		drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
1667		drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
1668	
1669		drm_sysfs_connector_add(connector);
1670	}]]></programlisting>
1671	      <para>
1672	        In the example above (taken from the i915 driver), a CRTC, connector and
1673	        encoder combination is created. A device-specific i2c bus is also
1674	        created for fetching EDID data and performing monitor detection. Once
1675	        the process is complete, the new connector is registered with sysfs to
1676	        make its properties available to applications.
1677	      </para>
1678	    </sect2>
1679	    <sect2>
1680	      <title>KMS API Functions</title>
1681	!Edrivers/gpu/drm/drm_crtc.c
1682	    </sect2>
1683	  </sect1>
1684	
1685	  <!-- Internals: kms helper functions -->
1686	
1687	  <sect1>
1688	    <title>Mode Setting Helper Functions</title>
1689	    <para>
1690	      The CRTC, encoder and connector functions provided by the drivers
1691	      implement the DRM API. They're called by the DRM core and ioctl handlers
1692	      to handle device state changes and configuration request. As implementing
1693	      those functions often requires logic not specific to drivers, mid-layer
1694	      helper functions are available to avoid duplicating boilerplate code.
1695	    </para>
1696	    <para>
1697	      The DRM core contains one mid-layer implementation. The mid-layer provides
1698	      implementations of several CRTC, encoder and connector functions (called
1699	      from the top of the mid-layer) that pre-process requests and call
1700	      lower-level functions provided by the driver (at the bottom of the
1701	      mid-layer). For instance, the
1702	      <function>drm_crtc_helper_set_config</function> function can be used to
1703	      fill the struct <structname>drm_crtc_funcs</structname>
1704	      <structfield>set_config</structfield> field. When called, it will split
1705	      the <methodname>set_config</methodname> operation in smaller, simpler
1706	      operations and call the driver to handle them.
1707	    </para>
1708	    <para>
1709	      To use the mid-layer, drivers call <function>drm_crtc_helper_add</function>,
1710	      <function>drm_encoder_helper_add</function> and
1711	      <function>drm_connector_helper_add</function> functions to install their
1712	      mid-layer bottom operations handlers, and fill the
1713	      <structname>drm_crtc_funcs</structname>,
1714	      <structname>drm_encoder_funcs</structname> and
1715	      <structname>drm_connector_funcs</structname> structures with pointers to
1716	      the mid-layer top API functions. Installing the mid-layer bottom operation
1717	      handlers is best done right after registering the corresponding KMS object.
1718	    </para>
1719	    <para>
1720	      The mid-layer is not split between CRTC, encoder and connector operations.
1721	      To use it, a driver must provide bottom functions for all of the three KMS
1722	      entities.
1723	    </para>
1724	    <sect2>
1725	      <title>Helper Functions</title>
1726	      <itemizedlist>
1727	        <listitem>
1728	          <synopsis>int drm_crtc_helper_set_config(struct drm_mode_set *set);</synopsis>
1729	          <para>
1730	            The <function>drm_crtc_helper_set_config</function> helper function
1731	            is a CRTC <methodname>set_config</methodname> implementation. It
1732	            first tries to locate the best encoder for each connector by calling
1733	            the connector <methodname>best_encoder</methodname> helper
1734	            operation.
1735	          </para>
1736	          <para>
1737	            After locating the appropriate encoders, the helper function will
1738	            call the <methodname>mode_fixup</methodname> encoder and CRTC helper
1739	            operations to adjust the requested mode, or reject it completely in
1740	            which case an error will be returned to the application. If the new
1741	            configuration after mode adjustment is identical to the current
1742	            configuration the helper function will return without performing any
1743	            other operation.
1744	          </para>
1745	          <para>
1746	            If the adjusted mode is identical to the current mode but changes to
1747	            the frame buffer need to be applied, the
1748	            <function>drm_crtc_helper_set_config</function> function will call
1749	            the CRTC <methodname>mode_set_base</methodname> helper operation. If
1750	            the adjusted mode differs from the current mode, or if the
1751	            <methodname>mode_set_base</methodname> helper operation is not
1752	            provided, the helper function performs a full mode set sequence by
1753	            calling the <methodname>prepare</methodname>,
1754	            <methodname>mode_set</methodname> and
1755	            <methodname>commit</methodname> CRTC and encoder helper operations,
1756	            in that order.
1757	          </para>
1758	        </listitem>
1759	        <listitem>
1760	          <synopsis>void drm_helper_connector_dpms(struct drm_connector *connector, int mode);</synopsis>
1761	          <para>
1762	            The <function>drm_helper_connector_dpms</function> helper function
1763	            is a connector <methodname>dpms</methodname> implementation that
1764	            tracks power state of connectors. To use the function, drivers must
1765	            provide <methodname>dpms</methodname> helper operations for CRTCs
1766	            and encoders to apply the DPMS state to the device.
1767	          </para>
1768	          <para>
1769	            The mid-layer doesn't track the power state of CRTCs and encoders.
1770	            The <methodname>dpms</methodname> helper operations can thus be
1771	            called with a mode identical to the currently active mode.
1772	          </para>
1773	        </listitem>
1774	        <listitem>
1775	          <synopsis>int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
1776	                                            uint32_t maxX, uint32_t maxY);</synopsis>
1777	          <para>
1778	            The <function>drm_helper_probe_single_connector_modes</function> helper
1779	            function is a connector <methodname>fill_modes</methodname>
1780	            implementation that updates the connection status for the connector
1781	            and then retrieves a list of modes by calling the connector
1782	            <methodname>get_modes</methodname> helper operation.
1783	          </para>
1784	          <para>
1785	            The function filters out modes larger than
1786	            <parameter>max_width</parameter> and <parameter>max_height</parameter>
1787	            if specified. It then calls the connector
1788	            <methodname>mode_valid</methodname> helper operation for  each mode in
1789	            the probed list to check whether the mode is valid for the connector.
1790	          </para>
1791	        </listitem>
1792	      </itemizedlist>
1793	    </sect2>
1794	    <sect2>
1795	      <title>CRTC Helper Operations</title>
1796	      <itemizedlist>
1797	        <listitem id="drm-helper-crtc-mode-fixup">
1798	          <synopsis>bool (*mode_fixup)(struct drm_crtc *crtc,
1799	                       const struct drm_display_mode *mode,
1800	                       struct drm_display_mode *adjusted_mode);</synopsis>
1801	          <para>
1802	            Let CRTCs adjust the requested mode or reject it completely. This
1803	            operation returns true if the mode is accepted (possibly after being
1804	            adjusted) or false if it is rejected.
1805	          </para>
1806	          <para>
1807	            The <methodname>mode_fixup</methodname> operation should reject the
1808	            mode if it can't reasonably use it. The definition of "reasonable"
1809	            is currently fuzzy in this context. One possible behaviour would be
1810	            to set the adjusted mode to the panel timings when a fixed-mode
1811	            panel is used with hardware capable of scaling. Another behaviour
1812	            would be to accept any input mode and adjust it to the closest mode
1813	            supported by the hardware (FIXME: This needs to be clarified).
1814	          </para>
1815	        </listitem>
1816	        <listitem>
1817	          <synopsis>int (*mode_set_base)(struct drm_crtc *crtc, int x, int y,
1818	                     struct drm_framebuffer *old_fb)</synopsis>
1819	          <para>
1820	            Move the CRTC on the current frame buffer (stored in
1821	            <literal>crtc-&gt;fb</literal>) to position (x,y). Any of the frame
1822	            buffer, x position or y position may have been modified.
1823	          </para>
1824	          <para>
1825	            This helper operation is optional. If not provided, the
1826	            <function>drm_crtc_helper_set_config</function> function will fall
1827	            back to the <methodname>mode_set</methodname> helper operation.
1828	          </para>
1829	          <note><para>
1830	            FIXME: Why are x and y passed as arguments, as they can be accessed
1831	            through <literal>crtc-&gt;x</literal> and
1832	            <literal>crtc-&gt;y</literal>?
1833	          </para></note>
1834	        </listitem>
1835	        <listitem>
1836	          <synopsis>void (*prepare)(struct drm_crtc *crtc);</synopsis>
1837	          <para>
1838	            Prepare the CRTC for mode setting. This operation is called after
1839	            validating the requested mode. Drivers use it to perform
1840	            device-specific operations required before setting the new mode.
1841	          </para>
1842	        </listitem>
1843	        <listitem>
1844	          <synopsis>int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode,
1845	                struct drm_display_mode *adjusted_mode, int x, int y,
1846	                struct drm_framebuffer *old_fb);</synopsis>
1847	          <para>
1848	            Set a new mode, position and frame buffer. Depending on the device
1849	            requirements, the mode can be stored internally by the driver and
1850	            applied in the <methodname>commit</methodname> operation, or
1851	            programmed to the hardware immediately.
1852	          </para>
1853	          <para>
1854	            The <methodname>mode_set</methodname> operation returns 0 on success
1855		    or a negative error code if an error occurs.
1856	          </para>
1857	        </listitem>
1858	        <listitem>
1859	          <synopsis>void (*commit)(struct drm_crtc *crtc);</synopsis>
1860	          <para>
1861	            Commit a mode. This operation is called after setting the new mode.
1862	            Upon return the device must use the new mode and be fully
1863	            operational.
1864	          </para>
1865	        </listitem>
1866	      </itemizedlist>
1867	    </sect2>
1868	    <sect2>
1869	      <title>Encoder Helper Operations</title>
1870	      <itemizedlist>
1871	        <listitem>
1872	          <synopsis>bool (*mode_fixup)(struct drm_encoder *encoder,
1873	                       const struct drm_display_mode *mode,
1874	                       struct drm_display_mode *adjusted_mode);</synopsis>
1875	          <para>
1876	            Let encoders adjust the requested mode or reject it completely. This
1877	            operation returns true if the mode is accepted (possibly after being
1878	            adjusted) or false if it is rejected. See the
1879	            <link linkend="drm-helper-crtc-mode-fixup">mode_fixup CRTC helper
1880	            operation</link> for an explanation of the allowed adjustments.
1881	          </para>
1882	        </listitem>
1883	        <listitem>
1884	          <synopsis>void (*prepare)(struct drm_encoder *encoder);</synopsis>
1885	          <para>
1886	            Prepare the encoder for mode setting. This operation is called after
1887	            validating the requested mode. Drivers use it to perform
1888	            device-specific operations required before setting the new mode.
1889	          </para>
1890	        </listitem>
1891	        <listitem>
1892	          <synopsis>void (*mode_set)(struct drm_encoder *encoder,
1893	                 struct drm_display_mode *mode,
1894	                 struct drm_display_mode *adjusted_mode);</synopsis>
1895	          <para>
1896	            Set a new mode. Depending on the device requirements, the mode can
1897	            be stored internally by the driver and applied in the
1898	            <methodname>commit</methodname> operation, or programmed to the
1899	            hardware immediately.
1900	          </para>
1901	        </listitem>
1902	        <listitem>
1903	          <synopsis>void (*commit)(struct drm_encoder *encoder);</synopsis>
1904	          <para>
1905	            Commit a mode. This operation is called after setting the new mode.
1906	            Upon return the device must use the new mode and be fully
1907	            operational.
1908	          </para>
1909	        </listitem>
1910	      </itemizedlist>
1911	    </sect2>
1912	    <sect2>
1913	      <title>Connector Helper Operations</title>
1914	      <itemizedlist>
1915	        <listitem>
1916	          <synopsis>struct drm_encoder *(*best_encoder)(struct drm_connector *connector);</synopsis>
1917	          <para>
1918	            Return a pointer to the best encoder for the connecter. Device that
1919	            map connectors to encoders 1:1 simply return the pointer to the
1920	            associated encoder. This operation is mandatory.
1921	          </para>
1922	        </listitem>
1923	        <listitem>
1924	          <synopsis>int (*get_modes)(struct drm_connector *connector);</synopsis>
1925	          <para>
1926	            Fill the connector's <structfield>probed_modes</structfield> list
1927	            by parsing EDID data with <function>drm_add_edid_modes</function> or
1928	            calling <function>drm_mode_probed_add</function> directly for every
1929	            supported mode and return the number of modes it has detected. This
1930	            operation is mandatory.
1931	          </para>
1932	          <para>
1933	            When adding modes manually the driver creates each mode with a call to
1934	            <function>drm_mode_create</function> and must fill the following fields.
1935	            <itemizedlist>
1936	              <listitem>
1937	                <synopsis>__u32 type;</synopsis>
1938	                <para>
1939	                  Mode type bitmask, a combination of
1940	                  <variablelist>
1941	                    <varlistentry>
1942	                      <term>DRM_MODE_TYPE_BUILTIN</term>
1943	                      <listitem><para>not used?</para></listitem>
1944	                    </varlistentry>
1945	                    <varlistentry>
1946	                      <term>DRM_MODE_TYPE_CLOCK_C</term>
1947	                      <listitem><para>not used?</para></listitem>
1948	                    </varlistentry>
1949	                    <varlistentry>
1950	                      <term>DRM_MODE_TYPE_CRTC_C</term>
1951	                      <listitem><para>not used?</para></listitem>
1952	                    </varlistentry>
1953	                    <varlistentry>
1954	                      <term>
1955	        DRM_MODE_TYPE_PREFERRED - The preferred mode for the connector
1956	                      </term>
1957	                      <listitem>
1958	                        <para>not used?</para>
1959	                      </listitem>
1960	                    </varlistentry>
1961	                    <varlistentry>
1962	                      <term>DRM_MODE_TYPE_DEFAULT</term>
1963	                      <listitem><para>not used?</para></listitem>
1964	                    </varlistentry>
1965	                    <varlistentry>
1966	                      <term>DRM_MODE_TYPE_USERDEF</term>
1967	                      <listitem><para>not used?</para></listitem>
1968	                    </varlistentry>
1969	                    <varlistentry>
1970	                      <term>DRM_MODE_TYPE_DRIVER</term>
1971	                      <listitem>
1972	                        <para>
1973	                          The mode has been created by the driver (as opposed to
1974	                          to user-created modes).
1975	                        </para>
1976	                      </listitem>
1977	                    </varlistentry>
1978	                  </variablelist>
1979	                  Drivers must set the DRM_MODE_TYPE_DRIVER bit for all modes they
1980	                  create, and set the DRM_MODE_TYPE_PREFERRED bit for the preferred
1981	                  mode.
1982	                </para>
1983	              </listitem>
1984	              <listitem>
1985	                <synopsis>__u32 clock;</synopsis>
1986	                <para>Pixel clock frequency in kHz unit</para>
1987	              </listitem>
1988	              <listitem>
1989	                <synopsis>__u16 hdisplay, hsync_start, hsync_end, htotal;
1990	    __u16 vdisplay, vsync_start, vsync_end, vtotal;</synopsis>
1991	                <para>Horizontal and vertical timing information</para>
1992	                <screen><![CDATA[
1993	             Active                 Front           Sync           Back
1994	             Region                 Porch                          Porch
1995	    <-----------------------><----------------><-------------><-------------->
1996	
1997	      //////////////////////|
1998	     ////////////////////// |
1999	    //////////////////////  |..................               ................
2000	                                               _______________
2001	
2002	    <----- [hv]display ----->
2003	    <------------- [hv]sync_start ------------>
2004	    <--------------------- [hv]sync_end --------------------->
2005	    <-------------------------------- [hv]total ----------------------------->
2006	]]></screen>
2007	              </listitem>
2008	              <listitem>
2009	                <synopsis>__u16 hskew;
2010	    __u16 vscan;</synopsis>
2011	                <para>Unknown</para>
2012	              </listitem>
2013	              <listitem>
2014	                <synopsis>__u32 flags;</synopsis>
2015	                <para>
2016	                  Mode flags, a combination of
2017	                  <variablelist>
2018	                    <varlistentry>
2019	                      <term>DRM_MODE_FLAG_PHSYNC</term>
2020	                      <listitem><para>
2021	                        Horizontal sync is active high
2022	                      </para></listitem>
2023	                    </varlistentry>
2024	                    <varlistentry>
2025	                      <term>DRM_MODE_FLAG_NHSYNC</term>
2026	                      <listitem><para>
2027	                        Horizontal sync is active low
2028	                      </para></listitem>
2029	                    </varlistentry>
2030	                    <varlistentry>
2031	                      <term>DRM_MODE_FLAG_PVSYNC</term>
2032	                      <listitem><para>
2033	                        Vertical sync is active high
2034	                      </para></listitem>
2035	                    </varlistentry>
2036	                    <varlistentry>
2037	                      <term>DRM_MODE_FLAG_NVSYNC</term>
2038	                      <listitem><para>
2039	                        Vertical sync is active low
2040	                      </para></listitem>
2041	                    </varlistentry>
2042	                    <varlistentry>
2043	                      <term>DRM_MODE_FLAG_INTERLACE</term>
2044	                      <listitem><para>
2045	                        Mode is interlaced
2046	                      </para></listitem>
2047	                    </varlistentry>
2048	                    <varlistentry>
2049	                      <term>DRM_MODE_FLAG_DBLSCAN</term>
2050	                      <listitem><para>
2051	                        Mode uses doublescan
2052	                      </para></listitem>
2053	                    </varlistentry>
2054	                    <varlistentry>
2055	                      <term>DRM_MODE_FLAG_CSYNC</term>
2056	                      <listitem><para>
2057	                        Mode uses composite sync
2058	                      </para></listitem>
2059	                    </varlistentry>
2060	                    <varlistentry>
2061	                      <term>DRM_MODE_FLAG_PCSYNC</term>
2062	                      <listitem><para>
2063	                        Composite sync is active high
2064	                      </para></listitem>
2065	                    </varlistentry>
2066	                    <varlistentry>
2067	                      <term>DRM_MODE_FLAG_NCSYNC</term>
2068	                      <listitem><para>
2069	                        Composite sync is active low
2070	                      </para></listitem>
2071	                    </varlistentry>
2072	                    <varlistentry>
2073	                      <term>DRM_MODE_FLAG_HSKEW</term>
2074	                      <listitem><para>
2075	                        hskew provided (not used?)
2076	                      </para></listitem>
2077	                    </varlistentry>
2078	                    <varlistentry>
2079	                      <term>DRM_MODE_FLAG_BCAST</term>
2080	                      <listitem><para>
2081	                        not used?
2082	                      </para></listitem>
2083	                    </varlistentry>
2084	                    <varlistentry>
2085	                      <term>DRM_MODE_FLAG_PIXMUX</term>
2086	                      <listitem><para>
2087	                        not used?
2088	                      </para></listitem>
2089	                    </varlistentry>
2090	                    <varlistentry>
2091	                      <term>DRM_MODE_FLAG_DBLCLK</term>
2092	                      <listitem><para>
2093	                        not used?
2094	                      </para></listitem>
2095	                    </varlistentry>
2096	                    <varlistentry>
2097	                      <term>DRM_MODE_FLAG_CLKDIV2</term>
2098	                      <listitem><para>
2099	                        ?
2100	                      </para></listitem>
2101	                    </varlistentry>
2102	                  </variablelist>
2103	                </para>
2104	                <para>
2105	                  Note that modes marked with the INTERLACE or DBLSCAN flags will be
2106	                  filtered out by
2107	                  <function>drm_helper_probe_single_connector_modes</function> if
2108	                  the connector's <structfield>interlace_allowed</structfield> or
2109	                  <structfield>doublescan_allowed</structfield> field is set to 0.
2110	                </para>
2111	              </listitem>
2112	              <listitem>
2113	                <synopsis>char name[DRM_DISPLAY_MODE_LEN];</synopsis>
2114	                <para>
2115	                  Mode name. The driver must call
2116	                  <function>drm_mode_set_name</function> to fill the mode name from
2117	                  <structfield>hdisplay</structfield>,
2118	                  <structfield>vdisplay</structfield> and interlace flag after
2119	                  filling the corresponding fields.
2120	                </para>
2121	              </listitem>
2122	            </itemizedlist>
2123	          </para>
2124	          <para>
2125	            The <structfield>vrefresh</structfield> value is computed by
2126	            <function>drm_helper_probe_single_connector_modes</function>.
2127	          </para>
2128	          <para>
2129	            When parsing EDID data, <function>drm_add_edid_modes</function> fill the
2130	            connector <structfield>display_info</structfield>
2131	            <structfield>width_mm</structfield> and
2132	            <structfield>height_mm</structfield> fields. When creating modes
2133	            manually the <methodname>get_modes</methodname> helper operation must
2134	            set the <structfield>display_info</structfield>
2135	            <structfield>width_mm</structfield> and
2136	            <structfield>height_mm</structfield> fields if they haven't been set
2137	            already (for instance at initilization time when a fixed-size panel is
2138	            attached to the connector). The mode <structfield>width_mm</structfield>
2139	            and <structfield>height_mm</structfield> fields are only used internally
2140	            during EDID parsing and should not be set when creating modes manually.
2141	          </para>
2142	        </listitem>
2143	        <listitem>
2144	          <synopsis>int (*mode_valid)(struct drm_connector *connector,
2145			  struct drm_display_mode *mode);</synopsis>
2146	          <para>
2147	            Verify whether a mode is valid for the connector. Return MODE_OK for
2148	            supported modes and one of the enum drm_mode_status values (MODE_*)
2149	            for unsupported modes. This operation is mandatory.
2150	          </para>
2151	          <para>
2152	            As the mode rejection reason is currently not used beside for
2153	            immediately removing the unsupported mode, an implementation can
2154	            return MODE_BAD regardless of the exact reason why the mode is not
2155	            valid.
2156	          </para>
2157	          <note><para>
2158	            Note that the <methodname>mode_valid</methodname> helper operation is
2159	            only called for modes detected by the device, and
2160	            <emphasis>not</emphasis> for modes set by the user through the CRTC
2161	            <methodname>set_config</methodname> operation.
2162	          </para></note>
2163	        </listitem>
2164	      </itemizedlist>
2165	    </sect2>
2166	    <sect2>
2167	      <title>Modeset Helper Functions Reference</title>
2168	!Edrivers/gpu/drm/drm_crtc_helper.c
2169	    </sect2>
2170	    <sect2>
2171	      <title>fbdev Helper Functions Reference</title>
2172	!Pdrivers/gpu/drm/drm_fb_helper.c fbdev helpers
2173	!Edrivers/gpu/drm/drm_fb_helper.c
2174	!Iinclude/drm/drm_fb_helper.h
2175	    </sect2>
2176	    <sect2>
2177	      <title>Display Port Helper Functions Reference</title>
2178	!Pdrivers/gpu/drm/drm_dp_helper.c dp helpers
2179	!Iinclude/drm/drm_dp_helper.h
2180	!Edrivers/gpu/drm/drm_dp_helper.c
2181	    </sect2>
2182	    <sect2>
2183	      <title>EDID Helper Functions Reference</title>
2184	!Edrivers/gpu/drm/drm_edid.c
2185	    </sect2>
2186	    <sect2>
2187	      <title>Rectangle Utilities Reference</title>
2188	!Pinclude/drm/drm_rect.h rect utils
2189	!Iinclude/drm/drm_rect.h
2190	!Edrivers/gpu/drm/drm_rect.c
2191	    </sect2>
2192	    <sect2>
2193	      <title>Flip-work Helper Reference</title>
2194	!Pinclude/drm/drm_flip_work.h flip utils
2195	!Iinclude/drm/drm_flip_work.h
2196	!Edrivers/gpu/drm/drm_flip_work.c
2197	    </sect2>
2198	    <sect2>
2199	      <title>VMA Offset Manager</title>
2200	!Pdrivers/gpu/drm/drm_vma_manager.c vma offset manager
2201	!Edrivers/gpu/drm/drm_vma_manager.c
2202	!Iinclude/drm/drm_vma_manager.h
2203	    </sect2>
2204	  </sect1>
2205	
2206	  <!-- Internals: kms properties -->
2207	
2208	  <sect1 id="drm-kms-properties">
2209	    <title>KMS Properties</title>
2210	    <para>
2211	      Drivers may need to expose additional parameters to applications than
2212	      those described in the previous sections. KMS supports attaching
2213	      properties to CRTCs, connectors and planes and offers a userspace API to
2214	      list, get and set the property values.
2215	    </para>
2216	    <para>
2217	      Properties are identified by a name that uniquely defines the property
2218	      purpose, and store an associated value. For all property types except blob
2219	      properties the value is a 64-bit unsigned integer.
2220	    </para>
2221	    <para>
2222	      KMS differentiates between properties and property instances. Drivers
2223	      first create properties and then create and associate individual instances
2224	      of those properties to objects. A property can be instantiated multiple
2225	      times and associated with different objects. Values are stored in property
2226	      instances, and all other property information are stored in the propery
2227	      and shared between all instances of the property.
2228	    </para>
2229	    <para>
2230	      Every property is created with a type that influences how the KMS core
2231	      handles the property. Supported property types are
2232	      <variablelist>
2233	        <varlistentry>
2234	          <term>DRM_MODE_PROP_RANGE</term>
2235	          <listitem><para>Range properties report their minimum and maximum
2236	            admissible values. The KMS core verifies that values set by
2237	            application fit in that range.</para></listitem>
2238	        </varlistentry>
2239	        <varlistentry>
2240	          <term>DRM_MODE_PROP_ENUM</term>
2241	          <listitem><para>Enumerated properties take a numerical value that
2242	            ranges from 0 to the number of enumerated values defined by the
2243	            property minus one, and associate a free-formed string name to each
2244	            value. Applications can retrieve the list of defined value-name pairs
2245	            and use the numerical value to get and set property instance values.
2246	            </para></listitem>
2247	        </varlistentry>
2248	        <varlistentry>
2249	          <term>DRM_MODE_PROP_BITMASK</term>
2250	          <listitem><para>Bitmask properties are enumeration properties that
2251	            additionally restrict all enumerated values to the 0..63 range.
2252	            Bitmask property instance values combine one or more of the
2253	            enumerated bits defined by the property.</para></listitem>
2254	        </varlistentry>
2255	        <varlistentry>
2256	          <term>DRM_MODE_PROP_BLOB</term>
2257	          <listitem><para>Blob properties store a binary blob without any format
2258	            restriction. The binary blobs are created as KMS standalone objects,
2259	            and blob property instance values store the ID of their associated
2260	            blob object.</para>
2261		    <para>Blob properties are only used for the connector EDID property
2262		    and cannot be created by drivers.</para></listitem>
2263	        </varlistentry>
2264	      </variablelist>
2265	    </para>
2266	    <para>
2267	      To create a property drivers call one of the following functions depending
2268	      on the property type. All property creation functions take property flags
2269	      and name, as well as type-specific arguments.
2270	      <itemizedlist>
2271	        <listitem>
2272	          <synopsis>struct drm_property *drm_property_create_range(struct drm_device *dev, int flags,
2273	                                               const char *name,
2274	                                               uint64_t min, uint64_t max);</synopsis>
2275	          <para>Create a range property with the given minimum and maximum
2276	            values.</para>
2277	        </listitem>
2278	        <listitem>
2279	          <synopsis>struct drm_property *drm_property_create_enum(struct drm_device *dev, int flags,
2280	                                              const char *name,
2281	                                              const struct drm_prop_enum_list *props,
2282	                                              int num_values);</synopsis>
2283	          <para>Create an enumerated property. The <parameter>props</parameter>
2284	            argument points to an array of <parameter>num_values</parameter>
2285	            value-name pairs.</para>
2286	        </listitem>
2287	        <listitem>
2288	          <synopsis>struct drm_property *drm_property_create_bitmask(struct drm_device *dev,
2289	                                                 int flags, const char *name,
2290	                                                 const struct drm_prop_enum_list *props,
2291	                                                 int num_values);</synopsis>
2292	          <para>Create a bitmask property. The <parameter>props</parameter>
2293	            argument points to an array of <parameter>num_values</parameter>
2294	            value-name pairs.</para>
2295	        </listitem>
2296	      </itemizedlist>
2297	    </para>
2298	    <para>
2299	      Properties can additionally be created as immutable, in which case they
2300	      will be read-only for applications but can be modified by the driver. To
2301	      create an immutable property drivers must set the DRM_MODE_PROP_IMMUTABLE
2302	      flag at property creation time.
2303	    </para>
2304	    <para>
2305	      When no array of value-name pairs is readily available at property
2306	      creation time for enumerated or range properties, drivers can create
2307	      the property using the <function>drm_property_create</function> function
2308	      and manually add enumeration value-name pairs by calling the
2309	      <function>drm_property_add_enum</function> function. Care must be taken to
2310	      properly specify the property type through the <parameter>flags</parameter>
2311	      argument.
2312	    </para>
2313	    <para>
2314	      After creating properties drivers can attach property instances to CRTC,
2315	      connector and plane objects by calling the
2316	      <function>drm_object_attach_property</function>. The function takes a
2317	      pointer to the target object, a pointer to the previously created property
2318	      and an initial instance value.
2319	    </para>
2320	  </sect1>
2321	
2322	  <!-- Internals: vertical blanking -->
2323	
2324	  <sect1 id="drm-vertical-blank">
2325	    <title>Vertical Blanking</title>
2326	    <para>
2327	      Vertical blanking plays a major role in graphics rendering. To achieve
2328	      tear-free display, users must synchronize page flips and/or rendering to
2329	      vertical blanking. The DRM API offers ioctls to perform page flips
2330	      synchronized to vertical blanking and wait for vertical blanking.
2331	    </para>
2332	    <para>
2333	      The DRM core handles most of the vertical blanking management logic, which
2334	      involves filtering out spurious interrupts, keeping race-free blanking
2335	      counters, coping with counter wrap-around and resets and keeping use
2336	      counts. It relies on the driver to generate vertical blanking interrupts
2337	      and optionally provide a hardware vertical blanking counter. Drivers must
2338	      implement the following operations.
2339	    </para>
2340	    <itemizedlist>
2341	      <listitem>
2342	        <synopsis>int (*enable_vblank) (struct drm_device *dev, int crtc);
2343	void (*disable_vblank) (struct drm_device *dev, int crtc);</synopsis>
2344	        <para>
2345		  Enable or disable vertical blanking interrupts for the given CRTC.
2346		</para>
2347	      </listitem>
2348	      <listitem>
2349	        <synopsis>u32 (*get_vblank_counter) (struct drm_device *dev, int crtc);</synopsis>
2350	        <para>
2351		  Retrieve the value of the vertical blanking counter for the given
2352		  CRTC. If the hardware maintains a vertical blanking counter its value
2353		  should be returned. Otherwise drivers can use the
2354		  <function>drm_vblank_count</function> helper function to handle this
2355		  operation.
2356		</para>
2357	      </listitem>
2358	    </itemizedlist>
2359	    <para>
2360	      Drivers must initialize the vertical blanking handling core with a call to
2361	      <function>drm_vblank_init</function> in their
2362	      <methodname>load</methodname> operation. The function will set the struct
2363	      <structname>drm_device</structname>
2364	      <structfield>vblank_disable_allowed</structfield> field to 0. This will
2365	      keep vertical blanking interrupts enabled permanently until the first mode
2366	      set operation, where <structfield>vblank_disable_allowed</structfield> is
2367	      set to 1. The reason behind this is not clear. Drivers can set the field
2368	      to 1 after <function>calling drm_vblank_init</function> to make vertical
2369	      blanking interrupts dynamically managed from the beginning.
2370	    </para>
2371	    <para>
2372	      Vertical blanking interrupts can be enabled by the DRM core or by drivers
2373	      themselves (for instance to handle page flipping operations). The DRM core
2374	      maintains a vertical blanking use count to ensure that the interrupts are
2375	      not disabled while a user still needs them. To increment the use count,
2376	      drivers call <function>drm_vblank_get</function>. Upon return vertical
2377	      blanking interrupts are guaranteed to be enabled.
2378	    </para>
2379	    <para>
2380	      To decrement the use count drivers call
2381	      <function>drm_vblank_put</function>. Only when the use count drops to zero
2382	      will the DRM core disable the vertical blanking interrupts after a delay
2383	      by scheduling a timer. The delay is accessible through the vblankoffdelay
2384	      module parameter or the <varname>drm_vblank_offdelay</varname> global
2385	      variable and expressed in milliseconds. Its default value is 5000 ms.
2386	    </para>
2387	    <para>
2388	      When a vertical blanking interrupt occurs drivers only need to call the
2389	      <function>drm_handle_vblank</function> function to account for the
2390	      interrupt.
2391	    </para>
2392	    <para>
2393	      Resources allocated by <function>drm_vblank_init</function> must be freed
2394	      with a call to <function>drm_vblank_cleanup</function> in the driver
2395	      <methodname>unload</methodname> operation handler.
2396	    </para>
2397	  </sect1>
2398	
2399	  <!-- Internals: open/close, file operations and ioctls -->
2400	
2401	  <sect1>
2402	    <title>Open/Close, File Operations and IOCTLs</title>
2403	    <sect2>
2404	      <title>Open and Close</title>
2405	      <synopsis>int (*firstopen) (struct drm_device *);
2406	void (*lastclose) (struct drm_device *);
2407	int (*open) (struct drm_device *, struct drm_file *);
2408	void (*preclose) (struct drm_device *, struct drm_file *);
2409	void (*postclose) (struct drm_device *, struct drm_file *);</synopsis>
2410	      <abstract>Open and close handlers. None of those methods are mandatory.
2411	      </abstract>
2412	      <para>
2413	        The <methodname>firstopen</methodname> method is called by the DRM core
2414		for legacy UMS (User Mode Setting) drivers only when an application
2415		opens a device that has no other opened file handle. UMS drivers can
2416		implement it to acquire device resources. KMS drivers can't use the
2417		method and must acquire resources in the <methodname>load</methodname>
2418		method instead.
2419	      </para>
2420	      <para>
2421		Similarly the <methodname>lastclose</methodname> method is called when
2422		the last application holding a file handle opened on the device closes
2423		it, for both UMS and KMS drivers. Additionally, the method is also
2424		called at module unload time or, for hot-pluggable devices, when the
2425		device is unplugged. The <methodname>firstopen</methodname> and
2426		<methodname>lastclose</methodname> calls can thus be unbalanced.
2427	      </para>
2428	      <para>
2429	        The <methodname>open</methodname> method is called every time the device
2430		is opened by an application. Drivers can allocate per-file private data
2431		in this method and store them in the struct
2432		<structname>drm_file</structname> <structfield>driver_priv</structfield>
2433		field. Note that the <methodname>open</methodname> method is called
2434		before <methodname>firstopen</methodname>.
2435	      </para>
2436	      <para>
2437	        The close operation is split into <methodname>preclose</methodname> and
2438		<methodname>postclose</methodname> methods. Drivers must stop and
2439		cleanup all per-file operations in the <methodname>preclose</methodname>
2440		method. For instance pending vertical blanking and page flip events must
2441		be cancelled. No per-file operation is allowed on the file handle after
2442		returning from the <methodname>preclose</methodname> method.
2443	      </para>
2444	      <para>
2445	        Finally the <methodname>postclose</methodname> method is called as the
2446		last step of the close operation, right before calling the
2447		<methodname>lastclose</methodname> method if no other open file handle
2448		exists for the device. Drivers that have allocated per-file private data
2449		in the <methodname>open</methodname> method should free it here.
2450	      </para>
2451	      <para>
2452	        The <methodname>lastclose</methodname> method should restore CRTC and
2453		plane properties to default value, so that a subsequent open of the
2454		device will not inherit state from the previous user. It can also be
2455		used to execute delayed power switching state changes, e.g. in
2456		conjunction with the vga-switcheroo infrastructure. Beyond that KMS
2457		drivers should not do any further cleanup. Only legacy UMS drivers might
2458		need to clean up device state so that the vga console or an independent
2459		fbdev driver could take over.
2460	      </para>
2461	    </sect2>
2462	    <sect2>
2463	      <title>File Operations</title>
2464	      <synopsis>const struct file_operations *fops</synopsis>
2465	      <abstract>File operations for the DRM device node.</abstract>
2466	      <para>
2467	        Drivers must define the file operations structure that forms the DRM
2468		userspace API entry point, even though most of those operations are
2469		implemented in the DRM core. The <methodname>open</methodname>,
2470		<methodname>release</methodname> and <methodname>ioctl</methodname>
2471		operations are handled by
2472		<programlisting>
2473		.owner = THIS_MODULE,
2474		.open = drm_open,
2475		.release = drm_release,
2476		.unlocked_ioctl = drm_ioctl,
2477	  #ifdef CONFIG_COMPAT
2478		.compat_ioctl = drm_compat_ioctl,
2479	  #endif
2480	        </programlisting>
2481	      </para>
2482	      <para>
2483	        Drivers that implement private ioctls that requires 32/64bit
2484		compatibility support must provide their own
2485		<methodname>compat_ioctl</methodname> handler that processes private
2486		ioctls and calls <function>drm_compat_ioctl</function> for core ioctls.
2487	      </para>
2488	      <para>
2489	        The <methodname>read</methodname> and <methodname>poll</methodname>
2490		operations provide support for reading DRM events and polling them. They
2491		are implemented by
2492		<programlisting>
2493		.poll = drm_poll,
2494		.read = drm_read,
2495		.llseek = no_llseek,
2496		</programlisting>
2497	      </para>
2498	      <para>
2499	        The memory mapping implementation varies depending on how the driver
2500		manages memory. Pre-GEM drivers will use <function>drm_mmap</function>,
2501		while GEM-aware drivers will use <function>drm_gem_mmap</function>. See
2502		<xref linkend="drm-gem"/>.
2503		<programlisting>
2504		.mmap = drm_gem_mmap,
2505		</programlisting>
2506	      </para>
2507	      <para>
2508	        No other file operation is supported by the DRM API.
2509	      </para>
2510	    </sect2>
2511	    <sect2>
2512	      <title>IOCTLs</title>
2513	      <synopsis>struct drm_ioctl_desc *ioctls;
2514	int num_ioctls;</synopsis>
2515	      <abstract>Driver-specific ioctls descriptors table.</abstract>
2516	      <para>
2517	        Driver-specific ioctls numbers start at DRM_COMMAND_BASE. The ioctls
2518		descriptors table is indexed by the ioctl number offset from the base
2519		value. Drivers can use the DRM_IOCTL_DEF_DRV() macro to initialize the
2520		table entries.
2521	      </para>
2522	      <para>
2523	        <programlisting>DRM_IOCTL_DEF_DRV(ioctl, func, flags)</programlisting>
2524		<para>
2525		  <parameter>ioctl</parameter> is the ioctl name. Drivers must define
2526		  the DRM_##ioctl and DRM_IOCTL_##ioctl macros to the ioctl number
2527		  offset from DRM_COMMAND_BASE and the ioctl number respectively. The
2528		  first macro is private to the device while the second must be exposed
2529		  to userspace in a public header.
2530		</para>
2531		<para>
2532		  <parameter>func</parameter> is a pointer to the ioctl handler function
2533		  compatible with the <type>drm_ioctl_t</type> type.
2534		  <programlisting>typedef int drm_ioctl_t(struct drm_device *dev, void *data,
2535			struct drm_file *file_priv);</programlisting>
2536		</para>
2537		<para>
2538		  <parameter>flags</parameter> is a bitmask combination of the following
2539		  values. It restricts how the ioctl is allowed to be called.
2540		  <itemizedlist>
2541		    <listitem><para>
2542		      DRM_AUTH - Only authenticated callers allowed
2543		    </para></listitem>
2544		    <listitem><para>
2545		      DRM_MASTER - The ioctl can only be called on the master file
2546		      handle
2547		    </para></listitem>
2548	            <listitem><para>
2549		      DRM_ROOT_ONLY - Only callers with the SYSADMIN capability allowed
2550		    </para></listitem>
2551	            <listitem><para>
2552		      DRM_CONTROL_ALLOW - The ioctl can only be called on a control
2553		      device
2554		    </para></listitem>
2555	            <listitem><para>
2556		      DRM_UNLOCKED - The ioctl handler will be called without locking
2557		      the DRM global mutex
2558		    </para></listitem>
2559		  </itemizedlist>
2560		</para>
2561	      </para>
2562	    </sect2>
2563	  </sect1>
2564	
2565	  <sect1>
2566	    <title>Command submission &amp; fencing</title>
2567	    <para>
2568	      This should cover a few device-specific command submission
2569	      implementations.
2570	    </para>
2571	  </sect1>
2572	
2573	  <!-- Internals: suspend/resume -->
2574	
2575	  <sect1>
2576	    <title>Suspend/Resume</title>
2577	    <para>
2578	      The DRM core provides some suspend/resume code, but drivers wanting full
2579	      suspend/resume support should provide save() and restore() functions.
2580	      These are called at suspend, hibernate, or resume time, and should perform
2581	      any state save or restore required by your device across suspend or
2582	      hibernate states.
2583	    </para>
2584	    <synopsis>int (*suspend) (struct drm_device *, pm_message_t state);
2585	int (*resume) (struct drm_device *);</synopsis>
2586	    <para>
2587	      Those are legacy suspend and resume methods. New driver should use the
2588	      power management interface provided by their bus type (usually through
2589	      the struct <structname>device_driver</structname> dev_pm_ops) and set
2590	      these methods to NULL.
2591	    </para>
2592	  </sect1>
2593	
2594	  <sect1>
2595	    <title>DMA services</title>
2596	    <para>
2597	      This should cover how DMA mapping etc. is supported by the core.
2598	      These functions are deprecated and should not be used.
2599	    </para>
2600	  </sect1>
2601	  </chapter>
2602	
2603	<!-- TODO
2604	
2605	- Add a glossary
2606	- Document the struct_mutex catch-all lock
2607	- Document connector properties
2608	
2609	- Why is the load method optional?
2610	- What are drivers supposed to set the initial display state to, and how?
2611	  Connector's DPMS states are not initialized and are thus equal to
2612	  DRM_MODE_DPMS_ON. The fbcon compatibility layer calls
2613	  drm_helper_disable_unused_functions(), which disables unused encoders and
2614	  CRTCs, but doesn't touch the connectors' DPMS state, and
2615	  drm_helper_connector_dpms() in reaction to fbdev blanking events. Do drivers
2616	  that don't implement (or just don't use) fbcon compatibility need to call
2617	  those functions themselves?
2618	- KMS drivers must call drm_vblank_pre_modeset() and drm_vblank_post_modeset()
2619	  around mode setting. Should this be done in the DRM core?
2620	- vblank_disable_allowed is set to 1 in the first drm_vblank_post_modeset()
2621	  call and never set back to 0. It seems to be safe to permanently set it to 1
2622	  in drm_vblank_init() for KMS driver, and it might be safe for UMS drivers as
2623	  well. This should be investigated.
2624	- crtc and connector .save and .restore operations are only used internally in
2625	  drivers, should they be removed from the core?
2626	- encoder mid-layer .save and .restore operations are only used internally in
2627	  drivers, should they be removed from the core?
2628	- encoder mid-layer .detect operation is only used internally in drivers,
2629	  should it be removed from the core?
2630	-->
2631	
2632	  <!-- External interfaces -->
2633	
2634	  <chapter id="drmExternals">
2635	    <title>Userland interfaces</title>
2636	    <para>
2637	      The DRM core exports several interfaces to applications,
2638	      generally intended to be used through corresponding libdrm
2639	      wrapper functions.  In addition, drivers export device-specific
2640	      interfaces for use by userspace drivers &amp; device-aware
2641	      applications through ioctls and sysfs files.
2642	    </para>
2643	    <para>
2644	      External interfaces include: memory mapping, context management,
2645	      DMA operations, AGP management, vblank control, fence
2646	      management, memory management, and output management.
2647	    </para>
2648	    <para>
2649	      Cover generic ioctls and sysfs layout here.  We only need high-level
2650	      info, since man pages should cover the rest.
2651	    </para>
2652	
2653	  <!-- External: render nodes -->
2654	
2655	    <sect1>
2656	      <title>Render nodes</title>
2657	      <para>
2658	        DRM core provides multiple character-devices for user-space to use.
2659	        Depending on which device is opened, user-space can perform a different
2660	        set of operations (mainly ioctls). The primary node is always created
2661	        and called <term>card&lt;num&gt;</term>. Additionally, a currently
2662	        unused control node, called <term>controlD&lt;num&gt;</term> is also
2663	        created. The primary node provides all legacy operations and
2664	        historically was the only interface used by userspace. With KMS, the
2665	        control node was introduced. However, the planned KMS control interface
2666	        has never been written and so the control node stays unused to date.
2667	      </para>
2668	      <para>
2669	        With the increased use of offscreen renderers and GPGPU applications,
2670	        clients no longer require running compositors or graphics servers to
2671	        make use of a GPU. But the DRM API required unprivileged clients to
2672	        authenticate to a DRM-Master prior to getting GPU access. To avoid this
2673	        step and to grant clients GPU access without authenticating, render
2674	        nodes were introduced. Render nodes solely serve render clients, that
2675	        is, no modesetting or privileged ioctls can be issued on render nodes.
2676	        Only non-global rendering commands are allowed. If a driver supports
2677	        render nodes, it must advertise it via the <term>DRIVER_RENDER</term>
2678	        DRM driver capability. If not supported, the primary node must be used
2679	        for render clients together with the legacy drmAuth authentication
2680	        procedure.
2681	      </para>
2682	      <para>
2683	        If a driver advertises render node support, DRM core will create a
2684	        separate render node called <term>renderD&lt;num&gt;</term>. There will
2685	        be one render node per device. No ioctls except  PRIME-related ioctls
2686	        will be allowed on this node. Especially <term>GEM_OPEN</term> will be
2687	        explicitly prohibited. Render nodes are designed to avoid the
2688	        buffer-leaks, which occur if clients guess the flink names or mmap
2689	        offsets on the legacy interface. Additionally to this basic interface,
2690	        drivers must mark their driver-dependent render-only ioctls as
2691	        <term>DRM_RENDER_ALLOW</term> so render clients can use them. Driver
2692	        authors must be careful not to allow any privileged ioctls on render
2693	        nodes.
2694	      </para>
2695	      <para>
2696	        With render nodes, user-space can now control access to the render node
2697	        via basic file-system access-modes. A running graphics server which
2698	        authenticates clients on the privileged primary/legacy node is no longer
2699	        required. Instead, a client can open the render node and is immediately
2700	        granted GPU access. Communication between clients (or servers) is done
2701	        via PRIME. FLINK from render node to legacy node is not supported. New
2702	        clients must not use the insecure FLINK interface.
2703	      </para>
2704	      <para>
2705	        Besides dropping all modeset/global ioctls, render nodes also drop the
2706	        DRM-Master concept. There is no reason to associate render clients with
2707	        a DRM-Master as they are independent of any graphics server. Besides,
2708	        they must work without any running master, anyway.
2709	        Drivers must be able to run without a master object if they support
2710	        render nodes. If, on the other hand, a driver requires shared state
2711	        between clients which is visible to user-space and accessible beyond
2712	        open-file boundaries, they cannot support render nodes.
2713	      </para>
2714	    </sect1>
2715	
2716	  <!-- External: vblank handling -->
2717	
2718	    <sect1>
2719	      <title>VBlank event handling</title>
2720	      <para>
2721	        The DRM core exposes two vertical blank related ioctls:
2722	        <variablelist>
2723	          <varlistentry>
2724	            <term>DRM_IOCTL_WAIT_VBLANK</term>
2725	            <listitem>
2726	              <para>
2727	                This takes a struct drm_wait_vblank structure as its argument,
2728	                and it is used to block or request a signal when a specified
2729	                vblank event occurs.
2730	              </para>
2731	            </listitem>
2732	          </varlistentry>
2733	          <varlistentry>
2734	            <term>DRM_IOCTL_MODESET_CTL</term>
2735	            <listitem>
2736	              <para>
2737	                This should be called by application level drivers before and
2738	                after mode setting, since on many devices the vertical blank
2739	                counter is reset at that time.  Internally, the DRM snapshots
2740	                the last vblank count when the ioctl is called with the
2741	                _DRM_PRE_MODESET command, so that the counter won't go backwards
2742	                (which is dealt with when _DRM_POST_MODESET is used).
2743	              </para>
2744	            </listitem>
2745	          </varlistentry>
2746	        </variablelist>
2747	<!--!Edrivers/char/drm/drm_irq.c-->
2748	      </para>
2749	    </sect1>
2750	
2751	  </chapter>
2752	
2753	  <!-- API reference -->
2754	
2755	  <appendix id="drmDriverApi">
2756	    <title>DRM Driver API</title>
2757	    <para>
2758	      Include auto-generated API reference here (need to reference it
2759	      from paragraphs above too).
2760	    </para>
2761	  </appendix>
2762	
2763	</book>
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