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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="LinuxKernelAPI">
6 <bookinfo>
7 <title>The Linux Kernel API</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_32.h
49!Iarch/x86/include/asm/unaligned.h
50 </sect1>
51
52 <sect1><title>Delaying, scheduling, and timer routines</title>
53!Iinclude/linux/sched.h
54!Ekernel/sched.c
55!Ekernel/timer.c
56 </sect1>
57 <sect1><title>High-resolution timers</title>
58!Iinclude/linux/ktime.h
59!Iinclude/linux/hrtimer.h
60!Ekernel/hrtimer.c
61 </sect1>
62 <sect1><title>Workqueues and Kevents</title>
63!Ekernel/workqueue.c
64 </sect1>
65 <sect1><title>Internal Functions</title>
66!Ikernel/exit.c
67!Ikernel/signal.c
68!Iinclude/linux/kthread.h
69!Ekernel/kthread.c
70 </sect1>
71
72 <sect1><title>Kernel objects manipulation</title>
73<!--
74X!Iinclude/linux/kobject.h
75-->
76!Elib/kobject.c
77 </sect1>
78
79 <sect1><title>Kernel utility functions</title>
80!Iinclude/linux/kernel.h
81!Ekernel/printk.c
82!Ekernel/panic.c
83!Ekernel/sys.c
84!Ekernel/rcupdate.c
85 </sect1>
86
87 <sect1><title>Device Resource Management</title>
88!Edrivers/base/devres.c
89 </sect1>
90
91 </chapter>
92
93 <chapter id="adt">
94 <title>Data Types</title>
95 <sect1><title>Doubly Linked Lists</title>
96!Iinclude/linux/list.h
97 </sect1>
98 </chapter>
99
100 <chapter id="libc">
101 <title>Basic C Library Functions</title>
102
103 <para>
104 When writing drivers, you cannot in general use routines which are
105 from the C Library. Some of the functions have been found generally
106 useful and they are listed below. The behaviour of these functions
107 may vary slightly from those defined by ANSI, and these deviations
108 are noted in the text.
109 </para>
110
111 <sect1><title>String Conversions</title>
112!Ilib/vsprintf.c
113!Elib/vsprintf.c
114 </sect1>
115 <sect1><title>String Manipulation</title>
116<!-- All functions are exported at now
117X!Ilib/string.c
118 -->
119!Elib/string.c
120 </sect1>
121 <sect1><title>Bit Operations</title>
122!Iarch/x86/include/asm/bitops.h
123 </sect1>
124 </chapter>
125
126 <chapter id="kernel-lib">
127 <title>Basic Kernel Library Functions</title>
128
129 <para>
130 The Linux kernel provides more basic utility functions.
131 </para>
132
133 <sect1><title>Bitmap Operations</title>
134!Elib/bitmap.c
135!Ilib/bitmap.c
136 </sect1>
137
138 <sect1><title>Command-line Parsing</title>
139!Elib/cmdline.c
140 </sect1>
141
142 <sect1 id="crc"><title>CRC Functions</title>
143!Elib/crc7.c
144!Elib/crc16.c
145!Elib/crc-itu-t.c
146!Elib/crc32.c
147!Elib/crc-ccitt.c
148 </sect1>
149 </chapter>
150
151 <chapter id="mm">
152 <title>Memory Management in Linux</title>
153 <sect1><title>The Slab Cache</title>
154!Iinclude/linux/slab.h
155!Emm/slab.c
156 </sect1>
157 <sect1><title>User Space Memory Access</title>
158!Iarch/x86/include/asm/uaccess_32.h
159!Earch/x86/lib/usercopy_32.c
160 </sect1>
161 <sect1><title>More Memory Management Functions</title>
162!Emm/readahead.c
163!Emm/filemap.c
164!Emm/memory.c
165!Emm/vmalloc.c
166!Imm/page_alloc.c
167!Emm/mempool.c
168!Emm/dmapool.c
169!Emm/page-writeback.c
170!Emm/truncate.c
171 </sect1>
172 </chapter>
173
174
175 <chapter id="ipc">
176 <title>Kernel IPC facilities</title>
177
178 <sect1><title>IPC utilities</title>
179!Iipc/util.c
180 </sect1>
181 </chapter>
182
183 <chapter id="kfifo">
184 <title>FIFO Buffer</title>
185 <sect1><title>kfifo interface</title>
186!Iinclude/linux/kfifo.h
187!Ekernel/kfifo.c
188 </sect1>
189 </chapter>
190
191 <chapter id="relayfs">
192 <title>relay interface support</title>
193
194 <para>
195 Relay interface support
196 is designed to provide an efficient mechanism for tools and
197 facilities to relay large amounts of data from kernel space to
198 user space.
199 </para>
200
201 <sect1><title>relay interface</title>
202!Ekernel/relay.c
203!Ikernel/relay.c
204 </sect1>
205 </chapter>
206
207 <chapter id="modload">
208 <title>Module Support</title>
209 <sect1><title>Module Loading</title>
210!Ekernel/kmod.c
211 </sect1>
212 <sect1><title>Inter Module support</title>
213 <para>
214 Refer to the file kernel/module.c for more information.
215 </para>
216<!-- FIXME: Removed for now since no structured comments in source
217X!Ekernel/module.c
218-->
219 </sect1>
220 </chapter>
221
222 <chapter id="hardware">
223 <title>Hardware Interfaces</title>
224 <sect1><title>Interrupt Handling</title>
225!Ekernel/irq/manage.c
226 </sect1>
227
228 <sect1><title>DMA Channels</title>
229!Ekernel/dma.c
230 </sect1>
231
232 <sect1><title>Resources Management</title>
233!Ikernel/resource.c
234!Ekernel/resource.c
235 </sect1>
236
237 <sect1><title>MTRR Handling</title>
238!Earch/x86/kernel/cpu/mtrr/main.c
239 </sect1>
240
241 <sect1><title>PCI Support Library</title>
242!Edrivers/pci/pci.c
243!Edrivers/pci/pci-driver.c
244!Edrivers/pci/remove.c
245!Edrivers/pci/pci-acpi.c
246!Edrivers/pci/search.c
247!Edrivers/pci/msi.c
248!Edrivers/pci/bus.c
249<!-- FIXME: Removed for now since no structured comments in source
250X!Edrivers/pci/hotplug.c
251-->
252!Edrivers/pci/probe.c
253!Edrivers/pci/rom.c
254 </sect1>
255 <sect1><title>PCI Hotplug Support Library</title>
256!Edrivers/pci/hotplug/pci_hotplug_core.c
257 </sect1>
258 <sect1><title>MCA Architecture</title>
259 <sect2><title>MCA Device Functions</title>
260 <para>
261 Refer to the file arch/x86/kernel/mca_32.c for more information.
262 </para>
263<!-- FIXME: Removed for now since no structured comments in source
264X!Earch/x86/kernel/mca_32.c
265-->
266 </sect2>
267 <sect2><title>MCA Bus DMA</title>
268!Iarch/x86/include/asm/mca_dma.h
269 </sect2>
270 </sect1>
271 </chapter>
272
273 <chapter id="firmware">
274 <title>Firmware Interfaces</title>
275 <sect1><title>DMI Interfaces</title>
276!Edrivers/firmware/dmi_scan.c
277 </sect1>
278 <sect1><title>EDD Interfaces</title>
279!Idrivers/firmware/edd.c
280 </sect1>
281 </chapter>
282
283 <chapter id="security">
284 <title>Security Framework</title>
285!Isecurity/security.c
286!Esecurity/inode.c
287 </chapter>
288
289 <chapter id="audit">
290 <title>Audit Interfaces</title>
291!Ekernel/audit.c
292!Ikernel/auditsc.c
293!Ikernel/auditfilter.c
294 </chapter>
295
296 <chapter id="accounting">
297 <title>Accounting Framework</title>
298!Ikernel/acct.c
299 </chapter>
300
301 <chapter id="devdrivers">
302 <title>Device drivers infrastructure</title>
303 <sect1><title>Device Drivers Base</title>
304<!--
305X!Iinclude/linux/device.h
306-->
307!Edrivers/base/driver.c
308!Edrivers/base/core.c
309!Edrivers/base/class.c
310!Edrivers/base/firmware_class.c
311!Edrivers/base/transport_class.c
312<!-- Cannot be included, because
313 attribute_container_add_class_device_adapter
314 and attribute_container_classdev_to_container
315 exceed allowed 44 characters maximum
316X!Edrivers/base/attribute_container.c
317-->
318!Edrivers/base/sys.c
319<!--
320X!Edrivers/base/interface.c
321-->
322!Edrivers/base/platform.c
323!Edrivers/base/bus.c
324 </sect1>
325 <sect1><title>Device Drivers Power Management</title>
326!Edrivers/base/power/main.c
327 </sect1>
328 <sect1><title>Device Drivers ACPI Support</title>
329<!-- Internal functions only
330X!Edrivers/acpi/sleep/main.c
331X!Edrivers/acpi/sleep/wakeup.c
332X!Edrivers/acpi/motherboard.c
333X!Edrivers/acpi/bus.c
334-->
335!Edrivers/acpi/scan.c
336!Idrivers/acpi/scan.c
337<!-- No correct structured comments
338X!Edrivers/acpi/pci_bind.c
339-->
340 </sect1>
341 <sect1><title>Device drivers PnP support</title>
342!Idrivers/pnp/core.c
343<!-- No correct structured comments
344X!Edrivers/pnp/system.c
345 -->
346!Edrivers/pnp/card.c
347!Idrivers/pnp/driver.c
348!Edrivers/pnp/manager.c
349!Edrivers/pnp/support.c
350 </sect1>
351 <sect1><title>Userspace IO devices</title>
352!Edrivers/uio/uio.c
353!Iinclude/linux/uio_driver.h
354 </sect1>
355 </chapter>
356
357 <chapter id="blkdev">
358 <title>Block Devices</title>
359!Eblock/blk-core.c
360!Iblock/blk-core.c
361!Eblock/blk-map.c
362!Iblock/blk-sysfs.c
363!Eblock/blk-settings.c
364!Eblock/blk-exec.c
365!Eblock/blk-barrier.c
366!Eblock/blk-tag.c
367!Iblock/blk-tag.c
368!Eblock/blk-integrity.c
369!Iblock/blktrace.c
370!Iblock/genhd.c
371!Eblock/genhd.c
372 </chapter>
373
374 <chapter id="chrdev">
375 <title>Char devices</title>
376!Efs/char_dev.c
377 </chapter>
378
379 <chapter id="miscdev">
380 <title>Miscellaneous Devices</title>
381!Edrivers/char/misc.c
382 </chapter>
383
384 <chapter id="parportdev">
385 <title>Parallel Port Devices</title>
386!Iinclude/linux/parport.h
387!Edrivers/parport/ieee1284.c
388!Edrivers/parport/share.c
389!Idrivers/parport/daisy.c
390 </chapter>
391
392 <chapter id="message_devices">
393 <title>Message-based devices</title>
394 <sect1><title>Fusion message devices</title>
395!Edrivers/message/fusion/mptbase.c
396!Idrivers/message/fusion/mptbase.c
397!Edrivers/message/fusion/mptscsih.c
398!Idrivers/message/fusion/mptscsih.c
399!Idrivers/message/fusion/mptctl.c
400!Idrivers/message/fusion/mptspi.c
401!Idrivers/message/fusion/mptfc.c
402!Idrivers/message/fusion/mptlan.c
403 </sect1>
404 <sect1><title>I2O message devices</title>
405!Iinclude/linux/i2o.h
406!Idrivers/message/i2o/core.h
407!Edrivers/message/i2o/iop.c
408!Idrivers/message/i2o/iop.c
409!Idrivers/message/i2o/config-osm.c
410!Edrivers/message/i2o/exec-osm.c
411!Idrivers/message/i2o/exec-osm.c
412!Idrivers/message/i2o/bus-osm.c
413!Edrivers/message/i2o/device.c
414!Idrivers/message/i2o/device.c
415!Idrivers/message/i2o/driver.c
416!Idrivers/message/i2o/pci.c
417!Idrivers/message/i2o/i2o_block.c
418!Idrivers/message/i2o/i2o_scsi.c
419!Idrivers/message/i2o/i2o_proc.c
420 </sect1>
421 </chapter>
422
423 <chapter id="snddev">
424 <title>Sound Devices</title>
425!Iinclude/sound/core.h
426!Esound/sound_core.c
427!Iinclude/sound/pcm.h
428!Esound/core/pcm.c
429!Esound/core/device.c
430!Esound/core/info.c
431!Esound/core/rawmidi.c
432!Esound/core/sound.c
433!Esound/core/memory.c
434!Esound/core/pcm_memory.c
435!Esound/core/init.c
436!Esound/core/isadma.c
437!Esound/core/control.c
438!Esound/core/pcm_lib.c
439!Esound/core/hwdep.c
440!Esound/core/pcm_native.c
441!Esound/core/memalloc.c
442<!-- FIXME: Removed for now since no structured comments in source
443X!Isound/sound_firmware.c
444-->
445 </chapter>
446
447 <chapter id="uart16x50">
448 <title>16x50 UART Driver</title>
449!Iinclude/linux/serial_core.h
450!Edrivers/serial/serial_core.c
451!Edrivers/serial/8250.c
452 </chapter>
453
454 <chapter id="fbdev">
455 <title>Frame Buffer Library</title>
456
457 <para>
458 The frame buffer drivers depend heavily on four data structures.
459 These structures are declared in include/linux/fb.h. They are
460 fb_info, fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs.
461 The last three can be made available to and from userland.
462 </para>
463
464 <para>
465 fb_info defines the current state of a particular video card.
466 Inside fb_info, there exists a fb_ops structure which is a
467 collection of needed functions to make fbdev and fbcon work.
468 fb_info is only visible to the kernel.
469 </para>
470
471 <para>
472 fb_var_screeninfo is used to describe the features of a video card
473 that are user defined. With fb_var_screeninfo, things such as
474 depth and the resolution may be defined.
475 </para>
476
477 <para>
478 The next structure is fb_fix_screeninfo. This defines the
479 properties of a card that are created when a mode is set and can't
480 be changed otherwise. A good example of this is the start of the
481 frame buffer memory. This "locks" the address of the frame buffer
482 memory, so that it cannot be changed or moved.
483 </para>
484
485 <para>
486 The last structure is fb_monospecs. In the old API, there was
487 little importance for fb_monospecs. This allowed for forbidden things
488 such as setting a mode of 800x600 on a fix frequency monitor. With
489 the new API, fb_monospecs prevents such things, and if used
490 correctly, can prevent a monitor from being cooked. fb_monospecs
491 will not be useful until kernels 2.5.x.
492 </para>
493
494 <sect1><title>Frame Buffer Memory</title>
495!Edrivers/video/fbmem.c
496 </sect1>
497<!--
498 <sect1><title>Frame Buffer Console</title>
499X!Edrivers/video/console/fbcon.c
500 </sect1>
501-->
502 <sect1><title>Frame Buffer Colormap</title>
503!Edrivers/video/fbcmap.c
504 </sect1>
505<!-- FIXME:
506 drivers/video/fbgen.c has no docs, which stuffs up the sgml. Comment
507 out until somebody adds docs. KAO
508 <sect1><title>Frame Buffer Generic Functions</title>
509X!Idrivers/video/fbgen.c
510 </sect1>
511KAO -->
512 <sect1><title>Frame Buffer Video Mode Database</title>
513!Idrivers/video/modedb.c
514!Edrivers/video/modedb.c
515 </sect1>
516 <sect1><title>Frame Buffer Macintosh Video Mode Database</title>
517!Edrivers/video/macmodes.c
518 </sect1>
519 <sect1><title>Frame Buffer Fonts</title>
520 <para>
521 Refer to the file drivers/video/console/fonts.c for more information.
522 </para>
523<!-- FIXME: Removed for now since no structured comments in source
524X!Idrivers/video/console/fonts.c
525-->
526 </sect1>
527 </chapter>
528
529 <chapter id="input_subsystem">
530 <title>Input Subsystem</title>
531!Iinclude/linux/input.h
532!Edrivers/input/input.c
533!Edrivers/input/ff-core.c
534!Edrivers/input/ff-memless.c
535 </chapter>
536
537 <chapter id="spi">
538 <title>Serial Peripheral Interface (SPI)</title>
539 <para>
540 SPI is the "Serial Peripheral Interface", widely used with
541 embedded systems because it is a simple and efficient
542 interface: basically a multiplexed shift register.
543 Its three signal wires hold a clock (SCK, often in the range
544 of 1-20 MHz), a "Master Out, Slave In" (MOSI) data line, and
545 a "Master In, Slave Out" (MISO) data line.
546 SPI is a full duplex protocol; for each bit shifted out the
547 MOSI line (one per clock) another is shifted in on the MISO line.
548 Those bits are assembled into words of various sizes on the
549 way to and from system memory.
550 An additional chipselect line is usually active-low (nCS);
551 four signals are normally used for each peripheral, plus
552 sometimes an interrupt.
553 </para>
554 <para>
555 The SPI bus facilities listed here provide a generalized
556 interface to declare SPI busses and devices, manage them
557 according to the standard Linux driver model, and perform
558 input/output operations.
559 At this time, only "master" side interfaces are supported,
560 where Linux talks to SPI peripherals and does not implement
561 such a peripheral itself.
562 (Interfaces to support implementing SPI slaves would
563 necessarily look different.)
564 </para>
565 <para>
566 The programming interface is structured around two kinds of driver,
567 and two kinds of device.
568 A "Controller Driver" abstracts the controller hardware, which may
569 be as simple as a set of GPIO pins or as complex as a pair of FIFOs
570 connected to dual DMA engines on the other side of the SPI shift
571 register (maximizing throughput). Such drivers bridge between
572 whatever bus they sit on (often the platform bus) and SPI, and
573 expose the SPI side of their device as a
574 <structname>struct spi_master</structname>.
575 SPI devices are children of that master, represented as a
576 <structname>struct spi_device</structname> and manufactured from
577 <structname>struct spi_board_info</structname> descriptors which
578 are usually provided by board-specific initialization code.
579 A <structname>struct spi_driver</structname> is called a
580 "Protocol Driver", and is bound to a spi_device using normal
581 driver model calls.
582 </para>
583 <para>
584 The I/O model is a set of queued messages. Protocol drivers
585 submit one or more <structname>struct spi_message</structname>
586 objects, which are processed and completed asynchronously.
587 (There are synchronous wrappers, however.) Messages are
588 built from one or more <structname>struct spi_transfer</structname>
589 objects, each of which wraps a full duplex SPI transfer.
590 A variety of protocol tweaking options are needed, because
591 different chips adopt very different policies for how they
592 use the bits transferred with SPI.
593 </para>
594!Iinclude/linux/spi/spi.h
595!Fdrivers/spi/spi.c spi_register_board_info
596!Edrivers/spi/spi.c
597 </chapter>
598
599 <chapter id="i2c">
600 <title>I<superscript>2</superscript>C and SMBus Subsystem</title>
601
602 <para>
603 I<superscript>2</superscript>C (or without fancy typography, "I2C")
604 is an acronym for the "Inter-IC" bus, a simple bus protocol which is
605 widely used where low data rate communications suffice.
606 Since it's also a licensed trademark, some vendors use another
607 name (such as "Two-Wire Interface", TWI) for the same bus.
608 I2C only needs two signals (SCL for clock, SDA for data), conserving
609 board real estate and minimizing signal quality issues.
610 Most I2C devices use seven bit addresses, and bus speeds of up
611 to 400 kHz; there's a high speed extension (3.4 MHz) that's not yet
612 found wide use.
613 I2C is a multi-master bus; open drain signaling is used to
614 arbitrate between masters, as well as to handshake and to
615 synchronize clocks from slower clients.
616 </para>
617
618 <para>
619 The Linux I2C programming interfaces support only the master
620 side of bus interactions, not the slave side.
621 The programming interface is structured around two kinds of driver,
622 and two kinds of device.
623 An I2C "Adapter Driver" abstracts the controller hardware; it binds
624 to a physical device (perhaps a PCI device or platform_device) and
625 exposes a <structname>struct i2c_adapter</structname> representing
626 each I2C bus segment it manages.
627 On each I2C bus segment will be I2C devices represented by a
628 <structname>struct i2c_client</structname>. Those devices will
629 be bound to a <structname>struct i2c_driver</structname>,
630 which should follow the standard Linux driver model.
631 (At this writing, a legacy model is more widely used.)
632 There are functions to perform various I2C protocol operations; at
633 this writing all such functions are usable only from task context.
634 </para>
635
636 <para>
637 The System Management Bus (SMBus) is a sibling protocol. Most SMBus
638 systems are also I2C conformant. The electrical constraints are
639 tighter for SMBus, and it standardizes particular protocol messages
640 and idioms. Controllers that support I2C can also support most
641 SMBus operations, but SMBus controllers don't support all the protocol
642 options that an I2C controller will.
643 There are functions to perform various SMBus protocol operations,
644 either using I2C primitives or by issuing SMBus commands to
645 i2c_adapter devices which don't support those I2C operations.
646 </para>
647
648!Iinclude/linux/i2c.h
649!Fdrivers/i2c/i2c-boardinfo.c i2c_register_board_info
650!Edrivers/i2c/i2c-core.c
651 </chapter>
652
653 <chapter id="clk">
654 <title>Clock Framework</title>
655
656 <para>
657 The clock framework defines programming interfaces to support
658 software management of the system clock tree.
659 This framework is widely used with System-On-Chip (SOC) platforms
660 to support power management and various devices which may need
661 custom clock rates.
662 Note that these "clocks" don't relate to timekeeping or real
663 time clocks (RTCs), each of which have separate frameworks.
664 These <structname>struct clk</structname> instances may be used
665 to manage for example a 96 MHz signal that is used to shift bits
666 into and out of peripherals or busses, or otherwise trigger
667 synchronous state machine transitions in system hardware.
668 </para>
669
670 <para>
671 Power management is supported by explicit software clock gating:
672 unused clocks are disabled, so the system doesn't waste power
673 changing the state of transistors that aren't in active use.
674 On some systems this may be backed by hardware clock gating,
675 where clocks are gated without being disabled in software.
676 Sections of chips that are powered but not clocked may be able
677 to retain their last state.
678 This low power state is often called a <emphasis>retention
679 mode</emphasis>.
680 This mode still incurs leakage currents, especially with finer
681 circuit geometries, but for CMOS circuits power is mostly used
682 by clocked state changes.
683 </para>
684
685 <para>
686 Power-aware drivers only enable their clocks when the device
687 they manage is in active use. Also, system sleep states often
688 differ according to which clock domains are active: while a
689 "standby" state may allow wakeup from several active domains, a
690 "mem" (suspend-to-RAM) state may require a more wholesale shutdown
691 of clocks derived from higher speed PLLs and oscillators, limiting
692 the number of possible wakeup event sources. A driver's suspend
693 method may need to be aware of system-specific clock constraints
694 on the target sleep state.
695 </para>
696
697 <para>
698 Some platforms support programmable clock generators. These
699 can be used by external chips of various kinds, such as other
700 CPUs, multimedia codecs, and devices with strict requirements
701 for interface clocking.
702 </para>
703
704!Iinclude/linux/clk.h
705 </chapter>
706
707</book>