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Based on kernel version 3.3. Page generated on 2012-03-23 21:28 EST.

	<?xml version="1.0" encoding="UTF-8"?>
	<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
		"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
	
	<book id="drmDevelopersGuide">
	  <bookinfo>
	    <title>Linux DRM Developer's Guide</title>
	
	    <copyright>
	      <year>2008-2009</year>
	      <holder>
		Intel Corporation (Jesse Barnes &lt;jesse.barnes@intel.com&gt;)
	      </holder>
	    </copyright>
	
	    <legalnotice>
	      <para>
		The contents of this file may be used under the terms of the GNU
		General Public License version 2 (the "GPL") as distributed in
		the kernel source COPYING file.
	      </para>
	    </legalnotice>
	  </bookinfo>
	
	<toc></toc>
	
	  <!-- Introduction -->
	
	  <chapter id="drmIntroduction">
	    <title>Introduction</title>
	    <para>
	      The Linux DRM layer contains code intended to support the needs
	      of complex graphics devices, usually containing programmable
	      pipelines well suited to 3D graphics acceleration.  Graphics
	      drivers in the kernel may make use of DRM functions to make
	      tasks like memory management, interrupt handling and DMA easier,
	      and provide a uniform interface to applications.
	    </para>
	    <para>
	      A note on versions: this guide covers features found in the DRM
	      tree, including the TTM memory manager, output configuration and
	      mode setting, and the new vblank internals, in addition to all
	      the regular features found in current kernels.
	    </para>
	    <para>
	      [Insert diagram of typical DRM stack here]
	    </para>
	  </chapter>
	
	  <!-- Internals -->
	
	  <chapter id="drmInternals">
	    <title>DRM Internals</title>
	    <para>
	      This chapter documents DRM internals relevant to driver authors
	      and developers working to add support for the latest features to
	      existing drivers.
	    </para>
	    <para>
	      First, we go over some typical driver initialization
	      requirements, like setting up command buffers, creating an
	      initial output configuration, and initializing core services.
	      Subsequent sections cover core internals in more detail,
	      providing implementation notes and examples.
	    </para>
	    <para>
	      The DRM layer provides several services to graphics drivers,
	      many of them driven by the application interfaces it provides
	      through libdrm, the library that wraps most of the DRM ioctls.
	      These include vblank event handling, memory
	      management, output management, framebuffer management, command
	      submission &amp; fencing, suspend/resume support, and DMA
	      services.
	    </para>
	    <para>
	      The core of every DRM driver is struct drm_driver.  Drivers
	      typically statically initialize a drm_driver structure,
	      then pass it to drm_init() at load time.
	    </para>
	
	  <!-- Internals: driver init -->
	
	  <sect1>
	    <title>Driver initialization</title>
	    <para>
	      Before calling the DRM initialization routines, the driver must
	      first create and fill out a struct drm_driver structure.
	    </para>
	    <programlisting>
	      static struct drm_driver driver = {
		/* Don't use MTRRs here; the Xserver or userspace app should
		 * deal with them for Intel hardware.
		 */
		.driver_features =
		    DRIVER_USE_AGP | DRIVER_REQUIRE_AGP |
		    DRIVER_HAVE_IRQ | DRIVER_IRQ_SHARED | DRIVER_MODESET,
		.load = i915_driver_load,
		.unload = i915_driver_unload,
		.firstopen = i915_driver_firstopen,
		.lastclose = i915_driver_lastclose,
		.preclose = i915_driver_preclose,
		.save = i915_save,
		.restore = i915_restore,
		.device_is_agp = i915_driver_device_is_agp,
		.get_vblank_counter = i915_get_vblank_counter,
		.enable_vblank = i915_enable_vblank,
		.disable_vblank = i915_disable_vblank,
		.irq_preinstall = i915_driver_irq_preinstall,
		.irq_postinstall = i915_driver_irq_postinstall,
		.irq_uninstall = i915_driver_irq_uninstall,
		.irq_handler = i915_driver_irq_handler,
		.reclaim_buffers = drm_core_reclaim_buffers,
		.get_map_ofs = drm_core_get_map_ofs,
		.get_reg_ofs = drm_core_get_reg_ofs,
		.fb_probe = intelfb_probe,
		.fb_remove = intelfb_remove,
		.fb_resize = intelfb_resize,
		.master_create = i915_master_create,
		.master_destroy = i915_master_destroy,
	#if defined(CONFIG_DEBUG_FS)
		.debugfs_init = i915_debugfs_init,
		.debugfs_cleanup = i915_debugfs_cleanup,
	#endif
		.gem_init_object = i915_gem_init_object,
		.gem_free_object = i915_gem_free_object,
		.gem_vm_ops = &amp;i915_gem_vm_ops,
		.ioctls = i915_ioctls,
		.fops = {
			.owner = THIS_MODULE,
			.open = drm_open,
			.release = drm_release,
			.ioctl = drm_ioctl,
			.mmap = drm_mmap,
			.poll = drm_poll,
			.fasync = drm_fasync,
	#ifdef CONFIG_COMPAT
			.compat_ioctl = i915_compat_ioctl,
	#endif
			.llseek = noop_llseek,
			},
		.pci_driver = {
			.name = DRIVER_NAME,
			.id_table = pciidlist,
			.probe = probe,
			.remove = __devexit_p(drm_cleanup_pci),
			},
		.name = DRIVER_NAME,
		.desc = DRIVER_DESC,
		.date = DRIVER_DATE,
		.major = DRIVER_MAJOR,
		.minor = DRIVER_MINOR,
		.patchlevel = DRIVER_PATCHLEVEL,
	      };
	    </programlisting>
	    <para>
	      In the example above, taken from the i915 DRM driver, the driver
	      sets several flags indicating what core features it supports;
	      we go over the individual callbacks in later sections.  Since
	      flags indicate which features your driver supports to the DRM
	      core, you need to set most of them prior to calling drm_init().  Some,
	      like DRIVER_MODESET can be set later based on user supplied parameters,
	      but that's the exception rather than the rule.
	    </para>
	    <variablelist>
	      <title>Driver flags</title>
	      <varlistentry>
		<term>DRIVER_USE_AGP</term>
		<listitem><para>
		    Driver uses AGP interface
		</para></listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_REQUIRE_AGP</term>
		<listitem><para>
		    Driver needs AGP interface to function.
		</para></listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_USE_MTRR</term>
		<listitem>
		  <para>
		    Driver uses MTRR interface for mapping memory.  Deprecated.
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_PCI_DMA</term>
		<listitem><para>
		    Driver is capable of PCI DMA.  Deprecated.
		</para></listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_SG</term>
		<listitem><para>
		    Driver can perform scatter/gather DMA.  Deprecated.
		</para></listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_HAVE_DMA</term>
		<listitem><para>Driver supports DMA.  Deprecated.</para></listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
		<listitem>
		  <para>
		    DRIVER_HAVE_IRQ indicates whether the driver has an IRQ
		    handler.  DRIVER_IRQ_SHARED indicates whether the device &amp;
		    handler support shared IRQs (note that this is required of
		    PCI drivers).
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_DMA_QUEUE</term>
		<listitem>
		  <para>
		    Should be set if the driver queues DMA requests and completes them
		    asynchronously.  Deprecated.
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_FB_DMA</term>
		<listitem>
		  <para>
		    Driver supports DMA to/from the framebuffer.  Deprecated.
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term>DRIVER_MODESET</term>
		<listitem>
		  <para>
		    Driver supports mode setting interfaces.
		  </para>
		</listitem>
	      </varlistentry>
	    </variablelist>
	    <para>
	      In this specific case, the driver requires AGP and supports
	      IRQs.  DMA, as discussed later, is handled by device-specific ioctls
	      in this case.  It also supports the kernel mode setting APIs, though
	      unlike in the actual i915 driver source, this example unconditionally
	      exports KMS capability.
	    </para>
	  </sect1>
	
	  <!-- Internals: driver load -->
	
	  <sect1>
	    <title>Driver load</title>
	    <para>
	      In the previous section, we saw what a typical drm_driver
	      structure might look like.  One of the more important fields in
	      the structure is the hook for the load function.
	    </para>
	    <programlisting>
	      static struct drm_driver driver = {
	      	...
	      	.load = i915_driver_load,
	        ...
	      };
	    </programlisting>
	    <para>
	      The load function has many responsibilities: allocating a driver
	      private structure, specifying supported performance counters,
	      configuring the device (e.g. mapping registers &amp; command
	      buffers), initializing the memory manager, and setting up the
	      initial output configuration.
	    </para>
	    <para>
	      If compatibility is a concern (e.g. with drivers converted over
	      to the new interfaces from the old ones), care must be taken to
	      prevent device initialization and control that is incompatible with
	      currently active userspace drivers.  For instance, if user
	      level mode setting drivers are in use, it would be problematic
	      to perform output discovery &amp; configuration at load time.
	      Likewise, if user-level drivers unaware of memory management are
	      in use, memory management and command buffer setup may need to
	      be omitted.  These requirements are driver-specific, and care
	      needs to be taken to keep both old and new applications and
	      libraries working.  The i915 driver supports the "modeset"
	      module parameter to control whether advanced features are
	      enabled at load time or in legacy fashion.
	    </para>
	
	    <sect2>
	      <title>Driver private &amp; performance counters</title>
	      <para>
		The driver private hangs off the main drm_device structure and
		can be used for tracking various device-specific bits of
		information, like register offsets, command buffer status,
		register state for suspend/resume, etc.  At load time, a
		driver may simply allocate one and set drm_device.dev_priv
		appropriately; it should be freed and drm_device.dev_priv set
		to NULL when the driver is unloaded.
	      </para>
	      <para>
		The DRM supports several counters which may be used for rough
		performance characterization.  Note that the DRM stat counter
		system is not often used by applications, and supporting
		additional counters is completely optional.
	      </para>
	      <para>
		These interfaces are deprecated and should not be used.  If performance
		monitoring is desired, the developer should investigate and
		potentially enhance the kernel perf and tracing infrastructure to export
		GPU related performance information for consumption by performance
		monitoring tools and applications.
	      </para>
	    </sect2>
	
	    <sect2>
	      <title>Configuring the device</title>
	      <para>
		Obviously, device configuration is device-specific.
		However, there are several common operations: finding a
		device's PCI resources, mapping them, and potentially setting
		up an IRQ handler.
	      </para>
	      <para>
		Finding &amp; mapping resources is fairly straightforward.  The
		DRM wrapper functions, drm_get_resource_start() and
		drm_get_resource_len(), may be used to find BARs on the given
		drm_device struct.  Once those values have been retrieved, the
		driver load function can call drm_addmap() to create a new
		mapping for the BAR in question.  Note that you probably want a
		drm_local_map_t in your driver private structure to track any
		mappings you create.
	<!-- !Fdrivers/gpu/drm/drm_bufs.c drm_get_resource_* -->
	<!-- !Finclude/drm/drmP.h drm_local_map_t -->
	      </para>
	      <para>
		if compatibility with other operating systems isn't a concern
		(DRM drivers can run under various BSD variants and OpenSolaris),
		native Linux calls may be used for the above, e.g. pci_resource_*
		and iomap*/iounmap.  See the Linux device driver book for more
		info.
	      </para>
	      <para>
		Once you have a register map, you may use the DRM_READn() and
		DRM_WRITEn() macros to access the registers on your device, or
		use driver-specific versions to offset into your MMIO space
		relative to a driver-specific base pointer (see I915_READ for
		an example).
	      </para>
	      <para>
		If your device supports interrupt generation, you may want to
		set up an interrupt handler when the driver is loaded.  This
		is done using the drm_irq_install() function.  If your device
		supports vertical blank interrupts, it should call
		drm_vblank_init() to initialize the core vblank handling code before
		enabling interrupts on your device.  This ensures the vblank related
		structures are allocated and allows the core to handle vblank events.
	      </para>
	<!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
	      <para>
		Once your interrupt handler is registered (it uses your
		drm_driver.irq_handler as the actual interrupt handling
		function), you can safely enable interrupts on your device,
		assuming any other state your interrupt handler uses is also
		initialized.
	      </para>
	      <para>
		Another task that may be necessary during configuration is
		mapping the video BIOS.  On many devices, the VBIOS describes
		device configuration, LCD panel timings (if any), and contains
		flags indicating device state.  Mapping the BIOS can be done
		using the pci_map_rom() call, a convenience function that
		takes care of mapping the actual ROM, whether it has been
		shadowed into memory (typically at address 0xc0000) or exists
		on the PCI device in the ROM BAR.  Note that after the ROM
		has been mapped and any necessary information has been extracted,
		it should be unmapped; on many devices, the ROM address decoder is
		shared with other BARs, so leaving it mapped could cause
		undesired behavior like hangs or memory corruption.
	<!--!Fdrivers/pci/rom.c pci_map_rom-->
	      </para>
	    </sect2>
	
	    <sect2>
	      <title>Memory manager initialization</title>
	      <para>
		In order to allocate command buffers, cursor memory, scanout
		buffers, etc., as well as support the latest features provided
		by packages like Mesa and the X.Org X server, your driver
		should support a memory manager.
	      </para>
	      <para>
		If your driver supports memory management (it should!), you
		need to set that up at load time as well.  How you initialize
		it depends on which memory manager you're using: TTM or GEM.
	      </para>
	      <sect3>
		<title>TTM initialization</title>
		<para>
		  TTM (for Translation Table Manager) manages video memory and
		  aperture space for graphics devices. TTM supports both UMA devices
		  and devices with dedicated video RAM (VRAM), i.e. most discrete
		  graphics devices.  If your device has dedicated RAM, supporting
		  TTM is desirable.  TTM also integrates tightly with your
		  driver-specific buffer execution function.  See the radeon
		  driver for examples.
		</para>
		<para>
		  The core TTM structure is the ttm_bo_driver struct.  It contains
		  several fields with function pointers for initializing the TTM,
		  allocating and freeing memory, waiting for command completion
		  and fence synchronization, and memory migration.  See the
		  radeon_ttm.c file for an example of usage.
		</para>
		<para>
		  The ttm_global_reference structure is made up of several fields:
		</para>
		<programlisting>
		  struct ttm_global_reference {
		  	enum ttm_global_types global_type;
		  	size_t size;
		  	void *object;
		  	int (*init) (struct ttm_global_reference *);
		  	void (*release) (struct ttm_global_reference *);
		  };
		</programlisting>
		<para>
		  There should be one global reference structure for your memory
		  manager as a whole, and there will be others for each object
		  created by the memory manager at runtime.  Your global TTM should
		  have a type of TTM_GLOBAL_TTM_MEM.  The size field for the global
		  object should be sizeof(struct ttm_mem_global), and the init and
		  release hooks should point at your driver-specific init and
		  release routines, which probably eventually call
		  ttm_mem_global_init and ttm_mem_global_release, respectively.
		</para>
		<para>
		  Once your global TTM accounting structure is set up and initialized
		  by calling ttm_global_item_ref() on it,
		  you need to create a buffer object TTM to
		  provide a pool for buffer object allocation by clients and the
		  kernel itself.  The type of this object should be TTM_GLOBAL_TTM_BO,
		  and its size should be sizeof(struct ttm_bo_global).  Again,
		  driver-specific init and release functions may be provided,
		  likely eventually calling ttm_bo_global_init() and
		  ttm_bo_global_release(), respectively.  Also, like the previous
		  object, ttm_global_item_ref() is used to create an initial reference
		  count for the TTM, which will call your initialization function.
		</para>
	      </sect3>
	      <sect3>
		<title>GEM initialization</title>
		<para>
		  GEM is an alternative to TTM, designed specifically for UMA
		  devices.  It has simpler initialization and execution requirements
		  than TTM, but has no VRAM management capability.  Core GEM
		  is initialized by calling drm_mm_init() to create
		  a GTT DRM MM object, which provides an address space pool for
		  object allocation.  In a KMS configuration, the driver
		  needs to allocate and initialize a command ring buffer following
		  core GEM initialization.  A UMA device usually has what is called a
		  "stolen" memory region, which provides space for the initial
		  framebuffer and large, contiguous memory regions required by the
		  device.  This space is not typically managed by GEM, and it must
		  be initialized separately into its own DRM MM object.
		</para>
		<para>
		  Initialization is driver-specific. In the case of Intel
		  integrated graphics chips like 965GM, GEM initialization can
		  be done by calling the internal GEM init function,
		  i915_gem_do_init().  Since the 965GM is a UMA device
		  (i.e. it doesn't have dedicated VRAM), GEM manages
		  making regular RAM available for GPU operations.  Memory set
		  aside by the BIOS (called "stolen" memory by the i915
		  driver) is managed by the DRM memrange allocator; the
		  rest of the aperture is managed by GEM.
		  <programlisting>
		    /* Basic memrange allocator for stolen space (aka vram) */
		    drm_memrange_init(&amp;dev_priv->vram, 0, prealloc_size);
		    /* Let GEM Manage from end of prealloc space to end of aperture */
		    i915_gem_do_init(dev, prealloc_size, agp_size);
		  </programlisting>
	<!--!Edrivers/char/drm/drm_memrange.c-->
		</para>
		<para>
		  Once the memory manager has been set up, we may allocate the
		  command buffer.  In the i915 case, this is also done with a
		  GEM function, i915_gem_init_ringbuffer().
		</para>
	      </sect3>
	    </sect2>
	
	    <sect2>
	      <title>Output configuration</title>
	      <para>
		The final initialization task is output configuration.  This involves:
		<itemizedlist>
		  <listitem>
		    Finding and initializing the CRTCs, encoders, and connectors
		    for the device.
		  </listitem>
		  <listitem>
		    Creating an initial configuration.
		  </listitem>
		  <listitem>
		    Registering a framebuffer console driver.
		  </listitem>
		</itemizedlist>
	      </para>
	      <sect3>
		<title>Output discovery and initialization</title>
		<para>
		  Several core functions exist to create CRTCs, encoders, and
		  connectors, namely: drm_crtc_init(), drm_connector_init(), and
		  drm_encoder_init(), along with several "helper" functions to
		  perform common tasks.
		</para>
		<para>
		  Connectors should be registered with sysfs once they've been
		  detected and initialized, using the
		  drm_sysfs_connector_add() function.  Likewise, when they're
		  removed from the system, they should be destroyed with
		  drm_sysfs_connector_remove().
		</para>
		<programlisting>
	<![CDATA[
	void intel_crt_init(struct drm_device *dev)
	{
		struct drm_connector *connector;
		struct intel_output *intel_output;
	
		intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
		if (!intel_output)
			return;
	
		connector = &intel_output->base;
		drm_connector_init(dev, &intel_output->base,
				   &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
	
		drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
				 DRM_MODE_ENCODER_DAC);
	
		drm_mode_connector_attach_encoder(&intel_output->base,
						  &intel_output->enc);
	
		/* Set up the DDC bus. */
		intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
		if (!intel_output->ddc_bus) {
			dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
				   "failed.\n");
			return;
		}
	
		intel_output->type = INTEL_OUTPUT_ANALOG;
		connector->interlace_allowed = 0;
		connector->doublescan_allowed = 0;
	
		drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
		drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
	
		drm_sysfs_connector_add(connector);
	}
	]]>
		</programlisting>
		<para>
		  In the example above (again, taken from the i915 driver), a
		  CRT connector and encoder combination is created.  A device-specific
		  i2c bus is also created for fetching EDID data and
		  performing monitor detection.  Once the process is complete,
		  the new connector is registered with sysfs to make its
		  properties available to applications.
		</para>
		<sect4>
		  <title>Helper functions and core functions</title>
		  <para>
		    Since many PC-class graphics devices have similar display output
		    designs, the DRM provides a set of helper functions to make
		    output management easier.  The core helper routines handle
		    encoder re-routing and the disabling of unused functions following
		    mode setting.  Using the helpers is optional, but recommended for
		    devices with PC-style architectures (i.e. a set of display planes
		    for feeding pixels to encoders which are in turn routed to
		    connectors).  Devices with more complex requirements needing
		    finer grained management may opt to use the core callbacks
		    directly.
		  </para>
		  <para>
		    [Insert typical diagram here.]  [Insert OMAP style config here.]
		  </para>
		</sect4>
		<para>
		  Each encoder object needs to provide:
		  <itemizedlist>
		    <listitem>
		      A DPMS (basically on/off) function.
		    </listitem>
		    <listitem>
		      A mode-fixup function (for converting requested modes into
		      native hardware timings).
		    </listitem>
		    <listitem>
		      Functions (prepare, set, and commit) for use by the core DRM
		      helper functions.
		    </listitem>
		  </itemizedlist>
		  Connector helpers need to provide functions (mode-fetch, validity,
		  and encoder-matching) for returning an ideal encoder for a given
		  connector.  The core connector functions include a DPMS callback,
		  save/restore routines (deprecated), detection, mode probing,
		  property handling, and cleanup functions.
		</para>
	<!--!Edrivers/char/drm/drm_crtc.h-->
	<!--!Edrivers/char/drm/drm_crtc.c-->
	<!--!Edrivers/char/drm/drm_crtc_helper.c-->
	      </sect3>
	    </sect2>
	  </sect1>
	
	  <!-- Internals: vblank handling -->
	
	  <sect1>
	    <title>VBlank event handling</title>
	    <para>
	      The DRM core exposes two vertical blank related ioctls:
	      <variablelist>
	        <varlistentry>
	          <term>DRM_IOCTL_WAIT_VBLANK</term>
	          <listitem>
	            <para>
	              This takes a struct drm_wait_vblank structure as its argument,
	              and it is used to block or request a signal when a specified
	              vblank event occurs.
	            </para>
	          </listitem>
	        </varlistentry>
	        <varlistentry>
	          <term>DRM_IOCTL_MODESET_CTL</term>
	          <listitem>
	            <para>
	              This should be called by application level drivers before and
	              after mode setting, since on many devices the vertical blank
	              counter is reset at that time.  Internally, the DRM snapshots
	              the last vblank count when the ioctl is called with the
	              _DRM_PRE_MODESET command, so that the counter won't go backwards
	              (which is dealt with when _DRM_POST_MODESET is used).
	            </para>
	          </listitem>
	        </varlistentry>
	      </variablelist>
	<!--!Edrivers/char/drm/drm_irq.c-->
	    </para>
	    <para>
	      To support the functions above, the DRM core provides several
	      helper functions for tracking vertical blank counters, and
	      requires drivers to provide several callbacks:
	      get_vblank_counter(), enable_vblank() and disable_vblank().  The
	      core uses get_vblank_counter() to keep the counter accurate
	      across interrupt disable periods.  It should return the current
	      vertical blank event count, which is often tracked in a device
	      register.  The enable and disable vblank callbacks should enable
	      and disable vertical blank interrupts, respectively.  In the
	      absence of DRM clients waiting on vblank events, the core DRM
	      code uses the disable_vblank() function to disable
	      interrupts, which saves power.  They are re-enabled again when
	      a client calls the vblank wait ioctl above.
	    </para>
	    <para>
	      A device that doesn't provide a count register may simply use an
	      internal atomic counter incremented on every vertical blank
	      interrupt (and then treat the enable_vblank() and disable_vblank()
	      callbacks as no-ops).
	    </para>
	  </sect1>
	
	  <sect1>
	    <title>Memory management</title>
	    <para>
	      The memory manager lies at the heart of many DRM operations; it
	      is required to support advanced client features like OpenGL
	      pbuffers.  The DRM currently contains two memory managers: TTM
	      and GEM.
	    </para>
	
	    <sect2>
	      <title>The Translation Table Manager (TTM)</title>
	      <para>
		TTM was developed by Tungsten Graphics, primarily by Thomas
		Hellström, and is intended to be a flexible, high performance
		graphics memory manager.
	      </para>
	      <para>
		Drivers wishing to support TTM must fill out a drm_bo_driver
		structure.
	      </para>
	      <para>
		TTM design background and information belongs here.
	      </para>
	    </sect2>
	
	    <sect2>
	      <title>The Graphics Execution Manager (GEM)</title>
	      <para>
		GEM is an Intel project, authored by Eric Anholt and Keith
		Packard.  It provides simpler interfaces than TTM, and is well
		suited for UMA devices.
	      </para>
	      <para>
		GEM-enabled drivers must provide gem_init_object() and
		gem_free_object() callbacks to support the core memory
		allocation routines.  They should also provide several driver-specific
		ioctls to support command execution, pinning, buffer
		read &amp; write, mapping, and domain ownership transfers.
	      </para>
	      <para>
		On a fundamental level, GEM involves several operations:
		<itemizedlist>
		  <listitem>Memory allocation and freeing</listitem>
		  <listitem>Command execution</listitem>
		  <listitem>Aperture management at command execution time</listitem>
		</itemizedlist>
		Buffer object allocation is relatively
		straightforward and largely provided by Linux's shmem layer, which
		provides memory to back each object.  When mapped into the GTT
		or used in a command buffer, the backing pages for an object are
		flushed to memory and marked write combined so as to be coherent
		with the GPU.  Likewise, if the CPU accesses an object after the GPU
		has finished rendering to the object, then the object must be made
		coherent with the CPU's view
		of memory, usually involving GPU cache flushing of various kinds.
		This core CPU&lt;-&gt;GPU coherency management is provided by a
		device-specific ioctl, which evaluates an object's current domain and
		performs any necessary flushing or synchronization to put the object
		into the desired coherency domain (note that the object may be busy,
		i.e. an active render target; in that case, setting the domain
		blocks the client and waits for rendering to complete before
		performing any necessary flushing operations).
	      </para>
	      <para>
		Perhaps the most important GEM function is providing a command
		execution interface to clients.  Client programs construct command
		buffers containing references to previously allocated memory objects,
		and then submit them to GEM.  At that point, GEM takes care to bind
		all the objects into the GTT, execute the buffer, and provide
		necessary synchronization between clients accessing the same buffers.
		This often involves evicting some objects from the GTT and re-binding
		others (a fairly expensive operation), and providing relocation
		support which hides fixed GTT offsets from clients.  Clients must
		take care not to submit command buffers that reference more objects
		than can fit in the GTT; otherwise, GEM will reject them and no rendering
		will occur.  Similarly, if several objects in the buffer require
		fence registers to be allocated for correct rendering (e.g. 2D blits
		on pre-965 chips), care must be taken not to require more fence
		registers than are available to the client.  Such resource management
		should be abstracted from the client in libdrm.
	      </para>
	    </sect2>
	
	  </sect1>
	
	  <!-- Output management -->
	  <sect1>
	    <title>Output management</title>
	    <para>
	      At the core of the DRM output management code is a set of
	      structures representing CRTCs, encoders, and connectors.
	    </para>
	    <para>
	      A CRTC is an abstraction representing a part of the chip that
	      contains a pointer to a scanout buffer.  Therefore, the number
	      of CRTCs available determines how many independent scanout
	      buffers can be active at any given time.  The CRTC structure
	      contains several fields to support this: a pointer to some video
	      memory, a display mode, and an (x, y) offset into the video
	      memory to support panning or configurations where one piece of
	      video memory spans multiple CRTCs.
	    </para>
	    <para>
	      An encoder takes pixel data from a CRTC and converts it to a
	      format suitable for any attached connectors.  On some devices,
	      it may be possible to have a CRTC send data to more than one
	      encoder.  In that case, both encoders would receive data from
	      the same scanout buffer, resulting in a "cloned" display
	      configuration across the connectors attached to each encoder.
	    </para>
	    <para>
	      A connector is the final destination for pixel data on a device,
	      and usually connects directly to an external display device like
	      a monitor or laptop panel.  A connector can only be attached to
	      one encoder at a time.  The connector is also the structure
	      where information about the attached display is kept, so it
	      contains fields for display data, EDID data, DPMS &amp;
	      connection status, and information about modes supported on the
	      attached displays.
	    </para>
	<!--!Edrivers/char/drm/drm_crtc.c-->
	  </sect1>
	
	  <sect1>
	    <title>Framebuffer management</title>
	    <para>
	      Clients need to provide a framebuffer object which provides a source
	      of pixels for a CRTC to deliver to the encoder(s) and ultimately the
	      connector(s). A framebuffer is fundamentally a driver-specific memory
	      object, made into an opaque handle by the DRM's addfb() function.
	      Once a framebuffer has been created this way, it may be passed to the
	      KMS mode setting routines for use in a completed configuration.
	    </para>
	  </sect1>
	
	  <sect1>
	    <title>Command submission &amp; fencing</title>
	    <para>
	      This should cover a few device-specific command submission
	      implementations.
	    </para>
	  </sect1>
	
	  <sect1>
	    <title>Suspend/resume</title>
	    <para>
	      The DRM core provides some suspend/resume code, but drivers
	      wanting full suspend/resume support should provide save() and
	      restore() functions.  These are called at suspend,
	      hibernate, or resume time, and should perform any state save or
	      restore required by your device across suspend or hibernate
	      states.
	    </para>
	  </sect1>
	
	  <sect1>
	    <title>DMA services</title>
	    <para>
	      This should cover how DMA mapping etc. is supported by the core.
	      These functions are deprecated and should not be used.
	    </para>
	  </sect1>
	  </chapter>
	
	  <!-- External interfaces -->
	
	  <chapter id="drmExternals">
	    <title>Userland interfaces</title>
	    <para>
	      The DRM core exports several interfaces to applications,
	      generally intended to be used through corresponding libdrm
	      wrapper functions.  In addition, drivers export device-specific
	      interfaces for use by userspace drivers &amp; device-aware
	      applications through ioctls and sysfs files.
	    </para>
	    <para>
	      External interfaces include: memory mapping, context management,
	      DMA operations, AGP management, vblank control, fence
	      management, memory management, and output management.
	    </para>
	    <para>
	      Cover generic ioctls and sysfs layout here.  We only need high-level
	      info, since man pages should cover the rest.
	    </para>
	  </chapter>
	
	  <!-- API reference -->
	
	  <appendix id="drmDriverApi">
	    <title>DRM Driver API</title>
	    <para>
	      Include auto-generated API reference here (need to reference it
	      from paragraphs above too).
	    </para>
	  </appendix>
	
	</book>

• [ DocBook ]
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