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Based on kernel version 4.8. Page generated on 2016-10-06 23:15 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="LinuxDriversAPI">
6	 <bookinfo>
7	  <title>Linux Device Drivers</title>
8	
9	  <legalnotice>
10	   <para>
11	     This documentation is free software; you can redistribute
12	     it and/or modify it under the terms of the GNU General Public
13	     License as published by the Free Software Foundation; either
14	     version 2 of the License, or (at your option) any later
15	     version.
16	   </para>
17	
18	   <para>
19	     This program is distributed in the hope that it will be
20	     useful, but WITHOUT ANY WARRANTY; without even the implied
21	     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
22	     See the GNU General Public License for more details.
23	   </para>
24	
25	   <para>
26	     You should have received a copy of the GNU General Public
27	     License along with this program; if not, write to the Free
28	     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
29	     MA 02111-1307 USA
30	   </para>
31	
32	   <para>
33	     For more details see the file COPYING in the source
34	     distribution of Linux.
35	   </para>
36	  </legalnotice>
37	 </bookinfo>
38	
39	<toc></toc>
40	
41	  <chapter id="Basics">
42	     <title>Driver Basics</title>
43	     <sect1><title>Driver Entry and Exit points</title>
44	!Iinclude/linux/init.h
45	     </sect1>
46	
47	     <sect1><title>Atomic and pointer manipulation</title>
48	!Iarch/x86/include/asm/atomic.h
49	     </sect1>
50	
51	     <sect1><title>Delaying, scheduling, and timer routines</title>
52	!Iinclude/linux/sched.h
53	!Ekernel/sched/core.c
54	!Ikernel/sched/cpupri.c
55	!Ikernel/sched/fair.c
56	!Iinclude/linux/completion.h
57	!Ekernel/time/timer.c
58	     </sect1>
59	     <sect1><title>Wait queues and Wake events</title>
60	!Iinclude/linux/wait.h
61	!Ekernel/sched/wait.c
62	     </sect1>
63	     <sect1><title>High-resolution timers</title>
64	!Iinclude/linux/ktime.h
65	!Iinclude/linux/hrtimer.h
66	!Ekernel/time/hrtimer.c
67	     </sect1>
68	     <sect1><title>Workqueues and Kevents</title>
69	!Iinclude/linux/workqueue.h
70	!Ekernel/workqueue.c
71	     </sect1>
72	     <sect1><title>Internal Functions</title>
73	!Ikernel/exit.c
74	!Ikernel/signal.c
75	!Iinclude/linux/kthread.h
76	!Ekernel/kthread.c
77	     </sect1>
78	
79	     <sect1><title>Kernel objects manipulation</title>
80	<!--
81	X!Iinclude/linux/kobject.h
82	-->
83	!Elib/kobject.c
84	     </sect1>
85	
86	     <sect1><title>Kernel utility functions</title>
87	!Iinclude/linux/kernel.h
88	!Ekernel/printk/printk.c
89	!Ekernel/panic.c
90	!Ekernel/sys.c
91	!Ekernel/rcu/srcu.c
92	!Ekernel/rcu/tree.c
93	!Ekernel/rcu/tree_plugin.h
94	!Ekernel/rcu/update.c
95	     </sect1>
96	
97	     <sect1><title>Device Resource Management</title>
98	!Edrivers/base/devres.c
99	     </sect1>
100	
101	  </chapter>
102	
103	  <chapter id="devdrivers">
104	     <title>Device drivers infrastructure</title>
105	     <sect1><title>The Basic Device Driver-Model Structures </title>
106	!Iinclude/linux/device.h
107	     </sect1>
108	     <sect1><title>Device Drivers Base</title>
109	!Idrivers/base/init.c
110	!Edrivers/base/driver.c
111	!Edrivers/base/core.c
112	!Edrivers/base/syscore.c
113	!Edrivers/base/class.c
114	!Idrivers/base/node.c
115	!Edrivers/base/firmware_class.c
116	!Edrivers/base/transport_class.c
117	<!-- Cannot be included, because
118	     attribute_container_add_class_device_adapter
119	 and attribute_container_classdev_to_container
120	     exceed allowed 44 characters maximum
121	X!Edrivers/base/attribute_container.c
122	-->
123	!Edrivers/base/dd.c
124	<!--
125	X!Edrivers/base/interface.c
126	-->
127	!Iinclude/linux/platform_device.h
128	!Edrivers/base/platform.c
129	!Edrivers/base/bus.c
130	     </sect1>
131	     <sect1>
132	       <title>Buffer Sharing and Synchronization</title>
133	       <para>
134	         The dma-buf subsystem provides the framework for sharing buffers
135	         for hardware (DMA) access across multiple device drivers and
136	         subsystems, and for synchronizing asynchronous hardware access.
137	       </para>
138	       <para>
139	         This is used, for example, by drm "prime" multi-GPU support, but
140	         is of course not limited to GPU use cases.
141	       </para>
142	       <para>
143	         The three main components of this are: (1) dma-buf, representing
144	         a sg_table and exposed to userspace as a file descriptor to allow
145	         passing between devices, (2) fence, which provides a mechanism
146	         to signal when one device as finished access, and (3) reservation,
147	         which manages the shared or exclusive fence(s) associated with
148	         the buffer.
149	       </para>
150	       <sect2><title>dma-buf</title>
151	!Edrivers/dma-buf/dma-buf.c
152	!Iinclude/linux/dma-buf.h
153	       </sect2>
154	       <sect2><title>reservation</title>
155	!Pdrivers/dma-buf/reservation.c Reservation Object Overview
156	!Edrivers/dma-buf/reservation.c
157	!Iinclude/linux/reservation.h
158	       </sect2>
159	       <sect2><title>fence</title>
160	!Edrivers/dma-buf/fence.c
161	!Iinclude/linux/fence.h
162	!Edrivers/dma-buf/seqno-fence.c
163	!Iinclude/linux/seqno-fence.h
164	!Edrivers/dma-buf/fence-array.c
165	!Iinclude/linux/fence-array.h
166	!Edrivers/dma-buf/reservation.c
167	!Iinclude/linux/reservation.h
168	!Edrivers/dma-buf/sync_file.c
169	!Iinclude/linux/sync_file.h
170	       </sect2>
171	     </sect1>
172	     <sect1><title>Device Drivers DMA Management</title>
173	!Edrivers/base/dma-coherent.c
174	!Edrivers/base/dma-mapping.c
175	     </sect1>
176	     <sect1><title>Device Drivers Power Management</title>
177	!Edrivers/base/power/main.c
178	     </sect1>
179	     <sect1><title>Device Drivers ACPI Support</title>
180	<!-- Internal functions only
181	X!Edrivers/acpi/sleep/main.c
182	X!Edrivers/acpi/sleep/wakeup.c
183	X!Edrivers/acpi/motherboard.c
184	X!Edrivers/acpi/bus.c
185	-->
186	!Edrivers/acpi/scan.c
187	!Idrivers/acpi/scan.c
188	<!-- No correct structured comments
189	X!Edrivers/acpi/pci_bind.c
190	-->
191	     </sect1>
192	     <sect1><title>Device drivers PnP support</title>
193	!Idrivers/pnp/core.c
194	<!-- No correct structured comments
195	X!Edrivers/pnp/system.c
196	 -->
197	!Edrivers/pnp/card.c
198	!Idrivers/pnp/driver.c
199	!Edrivers/pnp/manager.c
200	!Edrivers/pnp/support.c
201	     </sect1>
202	     <sect1><title>Userspace IO devices</title>
203	!Edrivers/uio/uio.c
204	!Iinclude/linux/uio_driver.h
205	     </sect1>
206	  </chapter>
207	
208	  <chapter id="parportdev">
209	     <title>Parallel Port Devices</title>
210	!Iinclude/linux/parport.h
211	!Edrivers/parport/ieee1284.c
212	!Edrivers/parport/share.c
213	!Idrivers/parport/daisy.c
214	  </chapter>
215	
216	  <chapter id="message_devices">
217		<title>Message-based devices</title>
218	     <sect1><title>Fusion message devices</title>
219	!Edrivers/message/fusion/mptbase.c
220	!Idrivers/message/fusion/mptbase.c
221	!Edrivers/message/fusion/mptscsih.c
222	!Idrivers/message/fusion/mptscsih.c
223	!Idrivers/message/fusion/mptctl.c
224	!Idrivers/message/fusion/mptspi.c
225	!Idrivers/message/fusion/mptfc.c
226	!Idrivers/message/fusion/mptlan.c
227	     </sect1>
228	  </chapter>
229	
230	  <chapter id="snddev">
231	     <title>Sound Devices</title>
232	!Iinclude/sound/core.h
233	!Esound/sound_core.c
234	!Iinclude/sound/pcm.h
235	!Esound/core/pcm.c
236	!Esound/core/device.c
237	!Esound/core/info.c
238	!Esound/core/rawmidi.c
239	!Esound/core/sound.c
240	!Esound/core/memory.c
241	!Esound/core/pcm_memory.c
242	!Esound/core/init.c
243	!Esound/core/isadma.c
244	!Esound/core/control.c
245	!Esound/core/pcm_lib.c
246	!Esound/core/hwdep.c
247	!Esound/core/pcm_native.c
248	!Esound/core/memalloc.c
249	<!-- FIXME: Removed for now since no structured comments in source
250	X!Isound/sound_firmware.c
251	-->
252	  </chapter>
253	
254	
255	  <chapter id="uart16x50">
256	     <title>16x50 UART Driver</title>
257	!Edrivers/tty/serial/serial_core.c
258	!Edrivers/tty/serial/8250/8250_core.c
259	  </chapter>
260	
261	  <chapter id="fbdev">
262	     <title>Frame Buffer Library</title>
263	
264	     <para>
265	       The frame buffer drivers depend heavily on four data structures.
266	       These structures are declared in include/linux/fb.h.  They are
267	       fb_info, fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs.
268	       The last three can be made available to and from userland.
269	     </para>
270	
271	     <para>
272	       fb_info defines the current state of a particular video card.
273	       Inside fb_info, there exists a fb_ops structure which is a
274	       collection of needed functions to make fbdev and fbcon work.
275	       fb_info is only visible to the kernel.
276	     </para>
277	
278	     <para>
279	       fb_var_screeninfo is used to describe the features of a video card
280	       that are user defined.  With fb_var_screeninfo, things such as
281	       depth and the resolution may be defined.
282	     </para>
283	
284	     <para>
285	       The next structure is fb_fix_screeninfo. This defines the
286	       properties of a card that are created when a mode is set and can't
287	       be changed otherwise.  A good example of this is the start of the
288	       frame buffer memory.  This "locks" the address of the frame buffer
289	       memory, so that it cannot be changed or moved.
290	     </para>
291	
292	     <para>
293	       The last structure is fb_monospecs. In the old API, there was
294	       little importance for fb_monospecs. This allowed for forbidden things
295	       such as setting a mode of 800x600 on a fix frequency monitor. With
296	       the new API, fb_monospecs prevents such things, and if used
297	       correctly, can prevent a monitor from being cooked.  fb_monospecs
298	       will not be useful until kernels 2.5.x.
299	     </para>
300	
301	     <sect1><title>Frame Buffer Memory</title>
302	!Edrivers/video/fbdev/core/fbmem.c
303	     </sect1>
304	<!--
305	     <sect1><title>Frame Buffer Console</title>
306	X!Edrivers/video/console/fbcon.c
307	     </sect1>
308	-->
309	     <sect1><title>Frame Buffer Colormap</title>
310	!Edrivers/video/fbdev/core/fbcmap.c
311	     </sect1>
312	<!-- FIXME:
313	  drivers/video/fbgen.c has no docs, which stuffs up the sgml.  Comment
314	  out until somebody adds docs.  KAO
315	     <sect1><title>Frame Buffer Generic Functions</title>
316	X!Idrivers/video/fbgen.c
317	     </sect1>
318	KAO -->
319	     <sect1><title>Frame Buffer Video Mode Database</title>
320	!Idrivers/video/fbdev/core/modedb.c
321	!Edrivers/video/fbdev/core/modedb.c
322	     </sect1>
323	     <sect1><title>Frame Buffer Macintosh Video Mode Database</title>
324	!Edrivers/video/fbdev/macmodes.c
325	     </sect1>
326	     <sect1><title>Frame Buffer Fonts</title>
327	        <para>
328	           Refer to the file lib/fonts/fonts.c for more information.
329	        </para>
330	<!-- FIXME: Removed for now since no structured comments in source
331	X!Ilib/fonts/fonts.c
332	-->
333	     </sect1>
334	  </chapter>
335	
336	  <chapter id="input_subsystem">
337	     <title>Input Subsystem</title>
338	     <sect1><title>Input core</title>
339	!Iinclude/linux/input.h
340	!Edrivers/input/input.c
341	!Edrivers/input/ff-core.c
342	!Edrivers/input/ff-memless.c
343	     </sect1>
344	     <sect1><title>Multitouch Library</title>
345	!Iinclude/linux/input/mt.h
346	!Edrivers/input/input-mt.c
347	     </sect1>
348	     <sect1><title>Polled input devices</title>
349	!Iinclude/linux/input-polldev.h
350	!Edrivers/input/input-polldev.c
351	     </sect1>
352	     <sect1><title>Matrix keyboards/keypads</title>
353	!Iinclude/linux/input/matrix_keypad.h
354	     </sect1>
355	     <sect1><title>Sparse keymap support</title>
356	!Iinclude/linux/input/sparse-keymap.h
357	!Edrivers/input/sparse-keymap.c
358	     </sect1>
359	  </chapter>
360	
361	  <chapter id="spi">
362	      <title>Serial Peripheral Interface (SPI)</title>
363	  <para>
364		SPI is the "Serial Peripheral Interface", widely used with
365		embedded systems because it is a simple and efficient
366		interface:  basically a multiplexed shift register.
367		Its three signal wires hold a clock (SCK, often in the range
368		of 1-20 MHz), a "Master Out, Slave In" (MOSI) data line, and
369		a "Master In, Slave Out" (MISO) data line.
370		SPI is a full duplex protocol; for each bit shifted out the
371		MOSI line (one per clock) another is shifted in on the MISO line.
372		Those bits are assembled into words of various sizes on the
373		way to and from system memory.
374		An additional chipselect line is usually active-low (nCS);
375		four signals are normally used for each peripheral, plus
376		sometimes an interrupt.
377	  </para>
378	  <para>
379		The SPI bus facilities listed here provide a generalized
380		interface to declare SPI busses and devices, manage them
381		according to the standard Linux driver model, and perform
382		input/output operations.
383		At this time, only "master" side interfaces are supported,
384		where Linux talks to SPI peripherals and does not implement
385		such a peripheral itself.
386		(Interfaces to support implementing SPI slaves would
387		necessarily look different.)
388	  </para>
389	  <para>
390		The programming interface is structured around two kinds of driver,
391		and two kinds of device.
392		A "Controller Driver" abstracts the controller hardware, which may
393		be as simple as a set of GPIO pins or as complex as a pair of FIFOs
394		connected to dual DMA engines on the other side of the SPI shift
395		register (maximizing throughput).  Such drivers bridge between
396		whatever bus they sit on (often the platform bus) and SPI, and
397		expose the SPI side of their device as a
398		<structname>struct spi_master</structname>.
399		SPI devices are children of that master, represented as a
400		<structname>struct spi_device</structname> and manufactured from
401		<structname>struct spi_board_info</structname> descriptors which
402		are usually provided by board-specific initialization code.
403		A <structname>struct spi_driver</structname> is called a
404		"Protocol Driver", and is bound to a spi_device using normal
405		driver model calls.
406	  </para>
407	  <para>
408		The I/O model is a set of queued messages.  Protocol drivers
409		submit one or more <structname>struct spi_message</structname>
410		objects, which are processed and completed asynchronously.
411		(There are synchronous wrappers, however.)  Messages are
412		built from one or more <structname>struct spi_transfer</structname>
413		objects, each of which wraps a full duplex SPI transfer.
414		A variety of protocol tweaking options are needed, because
415		different chips adopt very different policies for how they
416		use the bits transferred with SPI.
417	  </para>
418	!Iinclude/linux/spi/spi.h
419	!Fdrivers/spi/spi.c spi_register_board_info
420	!Edrivers/spi/spi.c
421	  </chapter>
422	
423	  <chapter id="i2c">
424	     <title>I<superscript>2</superscript>C and SMBus Subsystem</title>
425	
426	     <para>
427		I<superscript>2</superscript>C (or without fancy typography, "I2C")
428		is an acronym for the "Inter-IC" bus, a simple bus protocol which is
429		widely used where low data rate communications suffice.
430		Since it's also a licensed trademark, some vendors use another
431		name (such as "Two-Wire Interface", TWI) for the same bus.
432		I2C only needs two signals (SCL for clock, SDA for data), conserving
433		board real estate and minimizing signal quality issues.
434		Most I2C devices use seven bit addresses, and bus speeds of up
435		to 400 kHz; there's a high speed extension (3.4 MHz) that's not yet
436		found wide use.
437		I2C is a multi-master bus; open drain signaling is used to
438		arbitrate between masters, as well as to handshake and to
439		synchronize clocks from slower clients.
440	     </para>
441	
442	     <para>
443		The Linux I2C programming interfaces support only the master
444		side of bus interactions, not the slave side.
445		The programming interface is structured around two kinds of driver,
446		and two kinds of device.
447		An I2C "Adapter Driver" abstracts the controller hardware; it binds
448		to a physical device (perhaps a PCI device or platform_device) and
449		exposes a <structname>struct i2c_adapter</structname> representing
450		each I2C bus segment it manages.
451		On each I2C bus segment will be I2C devices represented by a
452		<structname>struct i2c_client</structname>.  Those devices will
453		be bound to a <structname>struct i2c_driver</structname>,
454		which should follow the standard Linux driver model.
455		(At this writing, a legacy model is more widely used.)
456		There are functions to perform various I2C protocol operations; at
457		this writing all such functions are usable only from task context.
458	     </para>
459	
460	     <para>
461		The System Management Bus (SMBus) is a sibling protocol.  Most SMBus
462		systems are also I2C conformant.  The electrical constraints are
463		tighter for SMBus, and it standardizes particular protocol messages
464		and idioms.  Controllers that support I2C can also support most
465		SMBus operations, but SMBus controllers don't support all the protocol
466		options that an I2C controller will.
467		There are functions to perform various SMBus protocol operations,
468		either using I2C primitives or by issuing SMBus commands to
469		i2c_adapter devices which don't support those I2C operations.
470	     </para>
471	
472	!Iinclude/linux/i2c.h
473	!Fdrivers/i2c/i2c-boardinfo.c i2c_register_board_info
474	!Edrivers/i2c/i2c-core.c
475	  </chapter>
476	
477	  <chapter id="hsi">
478	     <title>High Speed Synchronous Serial Interface (HSI)</title>
479	
480	     <para>
481		High Speed Synchronous Serial Interface (HSI) is a
482		serial interface mainly used for connecting application
483		engines (APE) with cellular modem engines (CMT) in cellular
484		handsets.
485	
486		HSI provides multiplexing for up to 16 logical channels,
487		low-latency and full duplex communication.
488	     </para>
489	
490	!Iinclude/linux/hsi/hsi.h
491	!Edrivers/hsi/hsi_core.c
492	  </chapter>
493	
494	  <chapter id="pwm">
495	    <title>Pulse-Width Modulation (PWM)</title>
496	    <para>
497	      Pulse-width modulation is a modulation technique primarily used to
498	      control power supplied to electrical devices.
499	    </para>
500	    <para>
501	      The PWM framework provides an abstraction for providers and consumers
502	      of PWM signals. A controller that provides one or more PWM signals is
503	      registered as <structname>struct pwm_chip</structname>. Providers are
504	      expected to embed this structure in a driver-specific structure. This
505	      structure contains fields that describe a particular chip.
506	    </para>
507	    <para>
508	      A chip exposes one or more PWM signal sources, each of which exposed
509	      as a <structname>struct pwm_device</structname>. Operations can be
510	      performed on PWM devices to control the period, duty cycle, polarity
511	      and active state of the signal.
512	    </para>
513	    <para>
514	      Note that PWM devices are exclusive resources: they can always only be
515	      used by one consumer at a time.
516	    </para>
517	!Iinclude/linux/pwm.h
518	!Edrivers/pwm/core.c
519	  </chapter>
520	
521	</book>
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