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" []>
5 <book id="LinuxKernelAPI">
7 <title>The Linux Kernel API</title>
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
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.
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,
33 For more details see the file COPYING in the source
34 distribution of Linux.
42 <title>Driver Basics</title>
43 <sect1><title>Driver Entry and Exit points</title>
44 !Iinclude/linux/init.h
47 <sect1><title>Atomic and pointer manipulation</title>
48 !Iinclude/asm-x86/atomic_32.h
49 !Iinclude/asm-x86/unaligned.h
52 <sect1><title>Delaying, scheduling, and timer routines</title>
53 !Iinclude/linux/sched.h
57 <sect1><title>High-resolution timers</title>
58 !Iinclude/linux/ktime.h
59 !Iinclude/linux/hrtimer.h
62 <sect1><title>Workqueues and Kevents</title>
65 <sect1><title>Internal Functions</title>
68 !Iinclude/linux/kthread.h
72 <sect1><title>Kernel objects manipulation</title>
74 X!Iinclude/linux/kobject.h
79 <sect1><title>Kernel utility functions</title>
80 !Iinclude/linux/kernel.h
87 <sect1><title>Device Resource Management</title>
88 !Edrivers/base/devres.c
94 <title>Data Types</title>
95 <sect1><title>Doubly Linked Lists</title>
96 !Iinclude/linux/list.h
101 <title>Basic C Library Functions</title>
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.
111 <sect1><title>String Conversions</title>
115 <sect1><title>String Manipulation</title>
116 <!-- All functions are exported at now
121 <sect1><title>Bit Operations</title>
122 !Iinclude/asm-x86/bitops.h
126 <chapter id="kernel-lib">
127 <title>Basic Kernel Library Functions</title>
130 The Linux kernel provides more basic utility functions.
133 <sect1><title>Bitmap Operations</title>
138 <sect1><title>Command-line Parsing</title>
142 <sect1 id="crc"><title>CRC Functions</title>
152 <title>Memory Management in Linux</title>
153 <sect1><title>The Slab Cache</title>
154 !Iinclude/linux/slab.h
157 <sect1><title>User Space Memory Access</title>
158 !Iinclude/asm-x86/uaccess_32.h
159 !Earch/x86/lib/usercopy_32.c
161 <sect1><title>More Memory Management Functions</title>
169 !Emm/page-writeback.c
176 <title>Kernel IPC facilities</title>
178 <sect1><title>IPC utilities</title>
184 <title>FIFO Buffer</title>
185 <sect1><title>kfifo interface</title>
186 !Iinclude/linux/kfifo.h
191 <chapter id="relayfs">
192 <title>relay interface support</title>
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
201 <sect1><title>relay interface</title>
207 <chapter id="modload">
208 <title>Module Support</title>
209 <sect1><title>Module Loading</title>
212 <sect1><title>Inter Module support</title>
214 Refer to the file kernel/module.c for more information.
216 <!-- FIXME: Removed for now since no structured comments in source
222 <chapter id="hardware">
223 <title>Hardware Interfaces</title>
224 <sect1><title>Interrupt Handling</title>
225 !Ekernel/irq/manage.c
228 <sect1><title>DMA Channels</title>
232 <sect1><title>Resources Management</title>
237 <sect1><title>MTRR Handling</title>
238 !Earch/x86/kernel/cpu/mtrr/main.c
241 <sect1><title>PCI Support Library</title>
243 !Edrivers/pci/pci-driver.c
244 !Edrivers/pci/remove.c
245 !Edrivers/pci/pci-acpi.c
246 !Edrivers/pci/search.c
249 <!-- FIXME: Removed for now since no structured comments in source
250 X!Edrivers/pci/hotplug.c
252 !Edrivers/pci/probe.c
255 <sect1><title>PCI Hotplug Support Library</title>
256 !Edrivers/pci/hotplug/pci_hotplug_core.c
258 <sect1><title>MCA Architecture</title>
259 <sect2><title>MCA Device Functions</title>
261 Refer to the file arch/x86/kernel/mca_32.c for more information.
263 <!-- FIXME: Removed for now since no structured comments in source
264 X!Earch/x86/kernel/mca_32.c
267 <sect2><title>MCA Bus DMA</title>
268 !Iinclude/asm-x86/mca_dma.h
273 <chapter id="firmware">
274 <title>Firmware Interfaces</title>
275 <sect1><title>DMI Interfaces</title>
276 !Edrivers/firmware/dmi_scan.c
278 <sect1><title>EDD Interfaces</title>
279 !Idrivers/firmware/edd.c
283 <chapter id="security">
284 <title>Security Framework</title>
285 !Isecurity/security.c
290 <title>Audit Interfaces</title>
293 !Ikernel/auditfilter.c
296 <chapter id="accounting">
297 <title>Accounting Framework</title>
301 <chapter id="devdrivers">
302 <title>Device drivers infrastructure</title>
303 <sect1><title>Device Drivers Base</title>
305 X!Iinclude/linux/device.h
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
316 X!Edrivers/base/attribute_container.c
320 X!Edrivers/base/interface.c
322 !Edrivers/base/platform.c
325 <sect1><title>Device Drivers Power Management</title>
326 !Edrivers/base/power/main.c
328 <sect1><title>Device Drivers ACPI Support</title>
329 <!-- Internal functions only
330 X!Edrivers/acpi/sleep/main.c
331 X!Edrivers/acpi/sleep/wakeup.c
332 X!Edrivers/acpi/motherboard.c
333 X!Edrivers/acpi/bus.c
335 !Edrivers/acpi/scan.c
336 !Idrivers/acpi/scan.c
337 <!-- No correct structured comments
338 X!Edrivers/acpi/pci_bind.c
341 <sect1><title>Device drivers PnP support</title>
343 <!-- No correct structured comments
344 X!Edrivers/pnp/system.c
347 !Idrivers/pnp/driver.c
348 !Edrivers/pnp/manager.c
349 !Edrivers/pnp/support.c
351 <sect1><title>Userspace IO devices</title>
353 !Iinclude/linux/uio_driver.h
357 <chapter id="blkdev">
358 <title>Block Devices</title>
363 !Eblock/blk-settings.c
365 !Eblock/blk-barrier.c
370 <chapter id="chrdev">
371 <title>Char devices</title>
375 <chapter id="miscdev">
376 <title>Miscellaneous Devices</title>
377 !Edrivers/char/misc.c
380 <chapter id="parportdev">
381 <title>Parallel Port Devices</title>
382 !Iinclude/linux/parport.h
383 !Edrivers/parport/ieee1284.c
384 !Edrivers/parport/share.c
385 !Idrivers/parport/daisy.c
388 <chapter id="message_devices">
389 <title>Message-based devices</title>
390 <sect1><title>Fusion message devices</title>
391 !Edrivers/message/fusion/mptbase.c
392 !Idrivers/message/fusion/mptbase.c
393 !Edrivers/message/fusion/mptscsih.c
394 !Idrivers/message/fusion/mptscsih.c
395 !Idrivers/message/fusion/mptctl.c
396 !Idrivers/message/fusion/mptspi.c
397 !Idrivers/message/fusion/mptfc.c
398 !Idrivers/message/fusion/mptlan.c
400 <sect1><title>I2O message devices</title>
401 !Iinclude/linux/i2o.h
402 !Idrivers/message/i2o/core.h
403 !Edrivers/message/i2o/iop.c
404 !Idrivers/message/i2o/iop.c
405 !Idrivers/message/i2o/config-osm.c
406 !Edrivers/message/i2o/exec-osm.c
407 !Idrivers/message/i2o/exec-osm.c
408 !Idrivers/message/i2o/bus-osm.c
409 !Edrivers/message/i2o/device.c
410 !Idrivers/message/i2o/device.c
411 !Idrivers/message/i2o/driver.c
412 !Idrivers/message/i2o/pci.c
413 !Idrivers/message/i2o/i2o_block.c
414 !Idrivers/message/i2o/i2o_scsi.c
415 !Idrivers/message/i2o/i2o_proc.c
419 <chapter id="snddev">
420 <title>Sound Devices</title>
421 !Iinclude/sound/core.h
423 !Iinclude/sound/pcm.h
425 !Esound/core/device.c
427 !Esound/core/rawmidi.c
429 !Esound/core/memory.c
430 !Esound/core/pcm_memory.c
432 !Esound/core/isadma.c
433 !Esound/core/control.c
434 !Esound/core/pcm_lib.c
436 !Esound/core/pcm_native.c
437 !Esound/core/memalloc.c
438 <!-- FIXME: Removed for now since no structured comments in source
439 X!Isound/sound_firmware.c
443 <chapter id="uart16x50">
444 <title>16x50 UART Driver</title>
445 !Iinclude/linux/serial_core.h
446 !Edrivers/serial/serial_core.c
447 !Edrivers/serial/8250.c
451 <title>Frame Buffer Library</title>
454 The frame buffer drivers depend heavily on four data structures.
455 These structures are declared in include/linux/fb.h. They are
456 fb_info, fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs.
457 The last three can be made available to and from userland.
461 fb_info defines the current state of a particular video card.
462 Inside fb_info, there exists a fb_ops structure which is a
463 collection of needed functions to make fbdev and fbcon work.
464 fb_info is only visible to the kernel.
468 fb_var_screeninfo is used to describe the features of a video card
469 that are user defined. With fb_var_screeninfo, things such as
470 depth and the resolution may be defined.
474 The next structure is fb_fix_screeninfo. This defines the
475 properties of a card that are created when a mode is set and can't
476 be changed otherwise. A good example of this is the start of the
477 frame buffer memory. This "locks" the address of the frame buffer
478 memory, so that it cannot be changed or moved.
482 The last structure is fb_monospecs. In the old API, there was
483 little importance for fb_monospecs. This allowed for forbidden things
484 such as setting a mode of 800x600 on a fix frequency monitor. With
485 the new API, fb_monospecs prevents such things, and if used
486 correctly, can prevent a monitor from being cooked. fb_monospecs
487 will not be useful until kernels 2.5.x.
490 <sect1><title>Frame Buffer Memory</title>
491 !Edrivers/video/fbmem.c
494 <sect1><title>Frame Buffer Console</title>
495 X!Edrivers/video/console/fbcon.c
498 <sect1><title>Frame Buffer Colormap</title>
499 !Edrivers/video/fbcmap.c
502 drivers/video/fbgen.c has no docs, which stuffs up the sgml. Comment
503 out until somebody adds docs. KAO
504 <sect1><title>Frame Buffer Generic Functions</title>
505 X!Idrivers/video/fbgen.c
508 <sect1><title>Frame Buffer Video Mode Database</title>
509 !Idrivers/video/modedb.c
510 !Edrivers/video/modedb.c
512 <sect1><title>Frame Buffer Macintosh Video Mode Database</title>
513 !Edrivers/video/macmodes.c
515 <sect1><title>Frame Buffer Fonts</title>
517 Refer to the file drivers/video/console/fonts.c for more information.
519 <!-- FIXME: Removed for now since no structured comments in source
520 X!Idrivers/video/console/fonts.c
525 <chapter id="input_subsystem">
526 <title>Input Subsystem</title>
527 !Iinclude/linux/input.h
528 !Edrivers/input/input.c
529 !Edrivers/input/ff-core.c
530 !Edrivers/input/ff-memless.c
534 <title>Serial Peripheral Interface (SPI)</title>
536 SPI is the "Serial Peripheral Interface", widely used with
537 embedded systems because it is a simple and efficient
538 interface: basically a multiplexed shift register.
539 Its three signal wires hold a clock (SCK, often in the range
540 of 1-20 MHz), a "Master Out, Slave In" (MOSI) data line, and
541 a "Master In, Slave Out" (MISO) data line.
542 SPI is a full duplex protocol; for each bit shifted out the
543 MOSI line (one per clock) another is shifted in on the MISO line.
544 Those bits are assembled into words of various sizes on the
545 way to and from system memory.
546 An additional chipselect line is usually active-low (nCS);
547 four signals are normally used for each peripheral, plus
548 sometimes an interrupt.
551 The SPI bus facilities listed here provide a generalized
552 interface to declare SPI busses and devices, manage them
553 according to the standard Linux driver model, and perform
554 input/output operations.
555 At this time, only "master" side interfaces are supported,
556 where Linux talks to SPI peripherals and does not implement
557 such a peripheral itself.
558 (Interfaces to support implementing SPI slaves would
559 necessarily look different.)
562 The programming interface is structured around two kinds of driver,
563 and two kinds of device.
564 A "Controller Driver" abstracts the controller hardware, which may
565 be as simple as a set of GPIO pins or as complex as a pair of FIFOs
566 connected to dual DMA engines on the other side of the SPI shift
567 register (maximizing throughput). Such drivers bridge between
568 whatever bus they sit on (often the platform bus) and SPI, and
569 expose the SPI side of their device as a
570 <structname>struct spi_master</structname>.
571 SPI devices are children of that master, represented as a
572 <structname>struct spi_device</structname> and manufactured from
573 <structname>struct spi_board_info</structname> descriptors which
574 are usually provided by board-specific initialization code.
575 A <structname>struct spi_driver</structname> is called a
576 "Protocol Driver", and is bound to a spi_device using normal
580 The I/O model is a set of queued messages. Protocol drivers
581 submit one or more <structname>struct spi_message</structname>
582 objects, which are processed and completed asynchronously.
583 (There are synchronous wrappers, however.) Messages are
584 built from one or more <structname>struct spi_transfer</structname>
585 objects, each of which wraps a full duplex SPI transfer.
586 A variety of protocol tweaking options are needed, because
587 different chips adopt very different policies for how they
588 use the bits transferred with SPI.
590 !Iinclude/linux/spi/spi.h
591 !Fdrivers/spi/spi.c spi_register_board_info
596 <title>I<superscript>2</superscript>C and SMBus Subsystem</title>
599 I<superscript>2</superscript>C (or without fancy typography, "I2C")
600 is an acronym for the "Inter-IC" bus, a simple bus protocol which is
601 widely used where low data rate communications suffice.
602 Since it's also a licensed trademark, some vendors use another
603 name (such as "Two-Wire Interface", TWI) for the same bus.
604 I2C only needs two signals (SCL for clock, SDA for data), conserving
605 board real estate and minimizing signal quality issues.
606 Most I2C devices use seven bit addresses, and bus speeds of up
607 to 400 kHz; there's a high speed extension (3.4 MHz) that's not yet
609 I2C is a multi-master bus; open drain signaling is used to
610 arbitrate between masters, as well as to handshake and to
611 synchronize clocks from slower clients.
615 The Linux I2C programming interfaces support only the master
616 side of bus interactions, not the slave side.
617 The programming interface is structured around two kinds of driver,
618 and two kinds of device.
619 An I2C "Adapter Driver" abstracts the controller hardware; it binds
620 to a physical device (perhaps a PCI device or platform_device) and
621 exposes a <structname>struct i2c_adapter</structname> representing
622 each I2C bus segment it manages.
623 On each I2C bus segment will be I2C devices represented by a
624 <structname>struct i2c_client</structname>. Those devices will
625 be bound to a <structname>struct i2c_driver</structname>,
626 which should follow the standard Linux driver model.
627 (At this writing, a legacy model is more widely used.)
628 There are functions to perform various I2C protocol operations; at
629 this writing all such functions are usable only from task context.
633 The System Management Bus (SMBus) is a sibling protocol. Most SMBus
634 systems are also I2C conformant. The electrical constraints are
635 tighter for SMBus, and it standardizes particular protocol messages
636 and idioms. Controllers that support I2C can also support most
637 SMBus operations, but SMBus controllers don't support all the protocol
638 options that an I2C controller will.
639 There are functions to perform various SMBus protocol operations,
640 either using I2C primitives or by issuing SMBus commands to
641 i2c_adapter devices which don't support those I2C operations.
644 !Iinclude/linux/i2c.h
645 !Fdrivers/i2c/i2c-boardinfo.c i2c_register_board_info
646 !Edrivers/i2c/i2c-core.c
650 <title>Clock Framework</title>
653 The clock framework defines programming interfaces to support
654 software management of the system clock tree.
655 This framework is widely used with System-On-Chip (SOC) platforms
656 to support power management and various devices which may need
658 Note that these "clocks" don't relate to timekeeping or real
659 time clocks (RTCs), each of which have separate frameworks.
660 These <structname>struct clk</structname> instances may be used
661 to manage for example a 96 MHz signal that is used to shift bits
662 into and out of peripherals or busses, or otherwise trigger
663 synchronous state machine transitions in system hardware.
667 Power management is supported by explicit software clock gating:
668 unused clocks are disabled, so the system doesn't waste power
669 changing the state of transistors that aren't in active use.
670 On some systems this may be backed by hardware clock gating,
671 where clocks are gated without being disabled in software.
672 Sections of chips that are powered but not clocked may be able
673 to retain their last state.
674 This low power state is often called a <emphasis>retention
676 This mode still incurs leakage currents, especially with finer
677 circuit geometries, but for CMOS circuits power is mostly used
678 by clocked state changes.
682 Power-aware drivers only enable their clocks when the device
683 they manage is in active use. Also, system sleep states often
684 differ according to which clock domains are active: while a
685 "standby" state may allow wakeup from several active domains, a
686 "mem" (suspend-to-RAM) state may require a more wholesale shutdown
687 of clocks derived from higher speed PLLs and oscillators, limiting
688 the number of possible wakeup event sources. A driver's suspend
689 method may need to be aware of system-specific clock constraints
690 on the target sleep state.
694 Some platforms support programmable clock generators. These
695 can be used by external chips of various kinds, such as other
696 CPUs, multimedia codecs, and devices with strict requirements
697 for interface clocking.
700 !Iinclude/linux/clk.h