Documentation/DocBook/kernel-api.tmpl

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   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 !Iinclude/asm-i386/atomic.h
  49 !Iinclude/asm-i386/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 <!--
  74 X!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
 117 X!Ilib/string.c
 118  -->
 119 !Elib/string.c
 120      </sect1>
 121      <sect1><title>Bit Operations</title>
 122 !Iinclude/asm-i386/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 !Iinclude/asm-i386/uaccess.h
 159 !Earch/i386/lib/usercopy.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/page-writeback.c
 169 !Emm/truncate.c
 170      </sect1>
 171   </chapter>
 172
 173
 174   <chapter id="ipc">
 175      <title>Kernel IPC facilities</title>
 176
 177      <sect1><title>IPC utilities</title>
 178 !Iipc/util.c
 179      </sect1>
 180   </chapter>
 181
 182   <chapter id="kfifo">
 183      <title>FIFO Buffer</title>
 184      <sect1><title>kfifo interface</title>
 185 !Iinclude/linux/kfifo.h
 186 !Ekernel/kfifo.c
 187      </sect1>
 188   </chapter>
 189
 190   <chapter id="relayfs">
 191      <title>relay interface support</title>
 192
 193      <para>
 194         Relay interface support
 195         is designed to provide an efficient mechanism for tools and
 196         facilities to relay large amounts of data from kernel space to
 197         user space.
 198      </para>
 199
 200      <sect1><title>relay interface</title>
 201 !Ekernel/relay.c
 202 !Ikernel/relay.c
 203      </sect1>
 204   </chapter>
 205
 206   <chapter id="netcore">
 207      <title>Linux Networking</title>
 208      <sect1><title>Networking Base Types</title>
 209 !Iinclude/linux/net.h
 210      </sect1>
 211      <sect1><title>Socket Buffer Functions</title>
 212 !Iinclude/linux/skbuff.h
 213 !Iinclude/net/sock.h
 214 !Enet/socket.c
 215 !Enet/core/skbuff.c
 216 !Enet/core/sock.c
 217 !Enet/core/datagram.c
 218 !Enet/core/stream.c
 219      </sect1>
 220      <sect1><title>Socket Filter</title>
 221 !Enet/core/filter.c
 222      </sect1>
 223      <sect1><title>Generic Network Statistics</title>
 224 !Iinclude/linux/gen_stats.h
 225 !Enet/core/gen_stats.c
 226 !Enet/core/gen_estimator.c
 227      </sect1>
 228      <sect1><title>SUN RPC subsystem</title>
 229 <!-- The !D functionality is not perfect, garbage has to be protected by comments
 230 !Dnet/sunrpc/sunrpc_syms.c
 231 -->
 232 !Enet/sunrpc/xdr.c
 233 !Enet/sunrpc/svcsock.c
 234 !Enet/sunrpc/sched.c
 235      </sect1>
 236   </chapter>
 237
 238   <chapter id="netdev">
 239      <title>Network device support</title>
 240      <sect1><title>Driver Support</title>
 241 !Enet/core/dev.c
 242 !Enet/ethernet/eth.c
 243 !Iinclude/linux/etherdevice.h
 244 !Edrivers/net/phy/phy.c
 245 !Idrivers/net/phy/phy.c
 246 !Edrivers/net/phy/phy_device.c
 247 !Idrivers/net/phy/phy_device.c
 248 !Edrivers/net/phy/mdio_bus.c
 249 !Idrivers/net/phy/mdio_bus.c
 250 <!-- FIXME: Removed for now since no structured comments in source
 251 X!Enet/core/wireless.c
 252 -->
 253      </sect1>
 254      <sect1><title>Synchronous PPP</title>
 255 !Edrivers/net/wan/syncppp.c
 256      </sect1>
 257   </chapter>
 258
 259   <chapter id="modload">
 260      <title>Module Support</title>
 261      <sect1><title>Module Loading</title>
 262 !Ekernel/kmod.c
 263      </sect1>
 264      <sect1><title>Inter Module support</title>
 265         <para>
 266            Refer to the file kernel/module.c for more information.
 267         </para>
 268 <!-- FIXME: Removed for now since no structured comments in source
 269 X!Ekernel/module.c
 270 -->
 271      </sect1>
 272   </chapter>
 273
 274   <chapter id="hardware">
 275      <title>Hardware Interfaces</title>
 276      <sect1><title>Interrupt Handling</title>
 277 !Ekernel/irq/manage.c
 278      </sect1>
 279
 280      <sect1><title>DMA Channels</title>
 281 !Ekernel/dma.c
 282      </sect1>
 283
 284      <sect1><title>Resources Management</title>
 285 !Ikernel/resource.c
 286 !Ekernel/resource.c
 287      </sect1>
 288
 289      <sect1><title>MTRR Handling</title>
 290 !Earch/i386/kernel/cpu/mtrr/main.c
 291      </sect1>
 292
 293      <sect1><title>PCI Support Library</title>
 294 !Edrivers/pci/pci.c
 295 !Edrivers/pci/pci-driver.c
 296 !Edrivers/pci/remove.c
 297 !Edrivers/pci/pci-acpi.c
 298 !Edrivers/pci/search.c
 299 !Edrivers/pci/msi.c
 300 !Edrivers/pci/bus.c
 301 <!-- FIXME: Removed for now since no structured comments in source
 302 X!Edrivers/pci/hotplug.c
 303 -->
 304 !Edrivers/pci/probe.c
 305 !Edrivers/pci/rom.c
 306      </sect1>
 307      <sect1><title>PCI Hotplug Support Library</title>
 308 !Edrivers/pci/hotplug/pci_hotplug_core.c
 309      </sect1>
 310      <sect1><title>MCA Architecture</title>
 311         <sect2><title>MCA Device Functions</title>
 312            <para>
 313               Refer to the file arch/i386/kernel/mca.c for more information.
 314            </para>
 315 <!-- FIXME: Removed for now since no structured comments in source
 316 X!Earch/i386/kernel/mca.c
 317 -->
 318         </sect2>
 319         <sect2><title>MCA Bus DMA</title>
 320 !Iinclude/asm-i386/mca_dma.h
 321         </sect2>
 322      </sect1>
 323   </chapter>
 324
 325   <chapter id="firmware">
 326      <title>Firmware Interfaces</title>
 327      <sect1><title>DMI Interfaces</title>
 328 !Edrivers/firmware/dmi_scan.c
 329      </sect1>
 330      <sect1><title>EDD Interfaces</title>
 331 !Idrivers/firmware/edd.c
 332      </sect1>
 333   </chapter>
 334
 335   <chapter id="security">
 336      <title>Security Framework</title>
 337 !Esecurity/security.c
 338   </chapter>
 339
 340   <chapter id="audit">
 341      <title>Audit Interfaces</title>
 342 !Ekernel/audit.c
 343 !Ikernel/auditsc.c
 344 !Ikernel/auditfilter.c
 345   </chapter>
 346
 347   <chapter id="accounting">
 348      <title>Accounting Framework</title>
 349 !Ikernel/acct.c
 350   </chapter>
 351
 352   <chapter id="pmfuncs">
 353      <title>Power Management</title>
 354 !Ekernel/power/pm.c
 355   </chapter>
 356
 357   <chapter id="devdrivers">
 358      <title>Device drivers infrastructure</title>
 359      <sect1><title>Device Drivers Base</title>
 360 <!--
 361 X!Iinclude/linux/device.h
 362 -->
 363 !Edrivers/base/driver.c
 364 !Edrivers/base/core.c
 365 !Edrivers/base/class.c
 366 !Edrivers/base/firmware_class.c
 367 !Edrivers/base/transport_class.c
 368 !Edrivers/base/dmapool.c
 369 <!-- Cannot be included, because
 370      attribute_container_add_class_device_adapter
 371  and attribute_container_classdev_to_container
 372      exceed allowed 44 characters maximum
 373 X!Edrivers/base/attribute_container.c
 374 -->
 375 !Edrivers/base/sys.c
 376 <!--
 377 X!Edrivers/base/interface.c
 378 -->
 379 !Edrivers/base/platform.c
 380 !Edrivers/base/bus.c
 381      </sect1>
 382      <sect1><title>Device Drivers Power Management</title>
 383 !Edrivers/base/power/main.c
 384 !Edrivers/base/power/resume.c
 385 !Edrivers/base/power/suspend.c
 386      </sect1>
 387      <sect1><title>Device Drivers ACPI Support</title>
 388 <!-- Internal functions only
 389 X!Edrivers/acpi/sleep/main.c
 390 X!Edrivers/acpi/sleep/wakeup.c
 391 X!Edrivers/acpi/motherboard.c
 392 X!Edrivers/acpi/bus.c
 393 -->
 394 !Edrivers/acpi/scan.c
 395 !Idrivers/acpi/scan.c
 396 <!-- No correct structured comments
 397 X!Edrivers/acpi/pci_bind.c
 398 -->
 399      </sect1>
 400      <sect1><title>Device drivers PnP support</title>
 401 !Edrivers/pnp/core.c
 402 <!-- No correct structured comments
 403 X!Edrivers/pnp/system.c
 404  -->
 405 !Edrivers/pnp/card.c
 406 !Edrivers/pnp/driver.c
 407 !Edrivers/pnp/manager.c
 408 !Edrivers/pnp/support.c
 409      </sect1>
 410      <sect1><title>Userspace IO devices</title>
 411 !Edrivers/uio/uio.c
 412 !Iinclude/linux/uio_driver.h
 413      </sect1>
 414   </chapter>
 415
 416   <chapter id="blkdev">
 417      <title>Block Devices</title>
 418 !Eblock/ll_rw_blk.c
 419   </chapter>
 420
 421   <chapter id="chrdev">
 422         <title>Char devices</title>
 423 !Efs/char_dev.c
 424   </chapter>
 425
 426   <chapter id="miscdev">
 427      <title>Miscellaneous Devices</title>
 428 !Edrivers/char/misc.c
 429   </chapter>
 430
 431   <chapter id="parportdev">
 432      <title>Parallel Port Devices</title>
 433 !Iinclude/linux/parport.h
 434 !Edrivers/parport/ieee1284.c
 435 !Edrivers/parport/share.c
 436 !Idrivers/parport/daisy.c
 437   </chapter>
 438
 439   <chapter id="message_devices">
 440         <title>Message-based devices</title>
 441      <sect1><title>Fusion message devices</title>
 442 !Edrivers/message/fusion/mptbase.c
 443 !Idrivers/message/fusion/mptbase.c
 444 !Edrivers/message/fusion/mptscsih.c
 445 !Idrivers/message/fusion/mptscsih.c
 446 !Idrivers/message/fusion/mptctl.c
 447 !Idrivers/message/fusion/mptspi.c
 448 !Idrivers/message/fusion/mptfc.c
 449 !Idrivers/message/fusion/mptlan.c
 450      </sect1>
 451      <sect1><title>I2O message devices</title>
 452 !Iinclude/linux/i2o.h
 453 !Idrivers/message/i2o/core.h
 454 !Edrivers/message/i2o/iop.c
 455 !Idrivers/message/i2o/iop.c
 456 !Idrivers/message/i2o/config-osm.c
 457 !Edrivers/message/i2o/exec-osm.c
 458 !Idrivers/message/i2o/exec-osm.c
 459 !Idrivers/message/i2o/bus-osm.c
 460 !Edrivers/message/i2o/device.c
 461 !Idrivers/message/i2o/device.c
 462 !Idrivers/message/i2o/driver.c
 463 !Idrivers/message/i2o/pci.c
 464 !Idrivers/message/i2o/i2o_block.c
 465 !Idrivers/message/i2o/i2o_scsi.c
 466 !Idrivers/message/i2o/i2o_proc.c
 467      </sect1>
 468   </chapter>
 469
 470   <chapter id="snddev">
 471      <title>Sound Devices</title>
 472 !Iinclude/sound/core.h
 473 !Esound/sound_core.c
 474 !Iinclude/sound/pcm.h
 475 !Esound/core/pcm.c
 476 !Esound/core/device.c
 477 !Esound/core/info.c
 478 !Esound/core/rawmidi.c
 479 !Esound/core/sound.c
 480 !Esound/core/memory.c
 481 !Esound/core/pcm_memory.c
 482 !Esound/core/init.c
 483 !Esound/core/isadma.c
 484 !Esound/core/control.c
 485 !Esound/core/pcm_lib.c
 486 !Esound/core/hwdep.c
 487 !Esound/core/pcm_native.c
 488 !Esound/core/memalloc.c
 489 <!-- FIXME: Removed for now since no structured comments in source
 490 X!Isound/sound_firmware.c
 491 -->
 492   </chapter>
 493
 494   <chapter id="uart16x50">
 495      <title>16x50 UART Driver</title>
 496 !Iinclude/linux/serial_core.h
 497 !Edrivers/serial/serial_core.c
 498 !Edrivers/serial/8250.c
 499   </chapter>
 500
 501   <chapter id="z85230">
 502      <title>Z85230 Support Library</title>
 503 !Edrivers/net/wan/z85230.c
 504   </chapter>
 505
 506   <chapter id="fbdev">
 507      <title>Frame Buffer Library</title>
 508
 509      <para>
 510        The frame buffer drivers depend heavily on four data structures.
 511        These structures are declared in include/linux/fb.h.  They are
 512        fb_info, fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs.
 513        The last three can be made available to and from userland.
 514      </para>
 515
 516      <para>
 517        fb_info defines the current state of a particular video card.
 518        Inside fb_info, there exists a fb_ops structure which is a
 519        collection of needed functions to make fbdev and fbcon work.
 520        fb_info is only visible to the kernel.
 521      </para>
 522
 523      <para>
 524        fb_var_screeninfo is used to describe the features of a video card
 525        that are user defined.  With fb_var_screeninfo, things such as
 526        depth and the resolution may be defined.
 527      </para>
 528
 529      <para>
 530        The next structure is fb_fix_screeninfo. This defines the
 531        properties of a card that are created when a mode is set and can't
 532        be changed otherwise.  A good example of this is the start of the
 533        frame buffer memory.  This "locks" the address of the frame buffer
 534        memory, so that it cannot be changed or moved.
 535      </para>
 536
 537      <para>
 538        The last structure is fb_monospecs. In the old API, there was
 539        little importance for fb_monospecs. This allowed for forbidden things
 540        such as setting a mode of 800x600 on a fix frequency monitor. With
 541        the new API, fb_monospecs prevents such things, and if used
 542        correctly, can prevent a monitor from being cooked.  fb_monospecs
 543        will not be useful until kernels 2.5.x.
 544      </para>
 545
 546      <sect1><title>Frame Buffer Memory</title>
 547 !Edrivers/video/fbmem.c
 548      </sect1>
 549 <!--
 550      <sect1><title>Frame Buffer Console</title>
 551 X!Edrivers/video/console/fbcon.c
 552      </sect1>
 553 -->
 554      <sect1><title>Frame Buffer Colormap</title>
 555 !Edrivers/video/fbcmap.c
 556      </sect1>
 557 <!-- FIXME:
 558   drivers/video/fbgen.c has no docs, which stuffs up the sgml.  Comment
 559   out until somebody adds docs.  KAO
 560      <sect1><title>Frame Buffer Generic Functions</title>
 561 X!Idrivers/video/fbgen.c
 562      </sect1>
 563 KAO -->
 564      <sect1><title>Frame Buffer Video Mode Database</title>
 565 !Idrivers/video/modedb.c
 566 !Edrivers/video/modedb.c
 567      </sect1>
 568      <sect1><title>Frame Buffer Macintosh Video Mode Database</title>
 569 !Edrivers/video/macmodes.c
 570      </sect1>
 571      <sect1><title>Frame Buffer Fonts</title>
 572         <para>
 573            Refer to the file drivers/video/console/fonts.c for more information.
 574         </para>
 575 <!-- FIXME: Removed for now since no structured comments in source
 576 X!Idrivers/video/console/fonts.c
 577 -->
 578      </sect1>
 579   </chapter>
 580
 581   <chapter id="input_subsystem">
 582      <title>Input Subsystem</title>
 583 !Iinclude/linux/input.h
 584 !Edrivers/input/input.c
 585 !Edrivers/input/ff-core.c
 586 !Edrivers/input/ff-memless.c
 587   </chapter>
 588
 589   <chapter id="spi">
 590       <title>Serial Peripheral Interface (SPI)</title>
 591   <para>
 592         SPI is the "Serial Peripheral Interface", widely used with
 593         embedded systems because it is a simple and efficient
 594         interface:  basically a multiplexed shift register.
 595         Its three signal wires hold a clock (SCK, often in the range
 596         of 1-20 MHz), a "Master Out, Slave In" (MOSI) data line, and
 597         a "Master In, Slave Out" (MISO) data line.
 598         SPI is a full duplex protocol; for each bit shifted out the
 599         MOSI line (one per clock) another is shifted in on the MISO line.
 600         Those bits are assembled into words of various sizes on the
 601         way to and from system memory.
 602         An additional chipselect line is usually active-low (nCS);
 603         four signals are normally used for each peripheral, plus
 604         sometimes an interrupt.
 605   </para>
 606   <para>
 607         The SPI bus facilities listed here provide a generalized
 608         interface to declare SPI busses and devices, manage them
 609         according to the standard Linux driver model, and perform
 610         input/output operations.
 611         At this time, only "master" side interfaces are supported,
 612         where Linux talks to SPI peripherals and does not implement
 613         such a peripheral itself.
 614         (Interfaces to support implementing SPI slaves would
 615         necessarily look different.)
 616   </para>
 617   <para>
 618         The programming interface is structured around two kinds of driver,
 619         and two kinds of device.
 620         A "Controller Driver" abstracts the controller hardware, which may
 621         be as simple as a set of GPIO pins or as complex as a pair of FIFOs
 622         connected to dual DMA engines on the other side of the SPI shift
 623         register (maximizing throughput).  Such drivers bridge between
 624         whatever bus they sit on (often the platform bus) and SPI, and
 625         expose the SPI side of their device as a
 626         <structname>struct spi_master</structname>.
 627         SPI devices are children of that master, represented as a
 628         <structname>struct spi_device</structname> and manufactured from
 629         <structname>struct spi_board_info</structname> descriptors which
 630         are usually provided by board-specific initialization code.
 631         A <structname>struct spi_driver</structname> is called a
 632         "Protocol Driver", and is bound to a spi_device using normal
 633         driver model calls.
 634   </para>
 635   <para>
 636         The I/O model is a set of queued messages.  Protocol drivers
 637         submit one or more <structname>struct spi_message</structname>
 638         objects, which are processed and completed asynchronously.
 639         (There are synchronous wrappers, however.)  Messages are
 640         built from one or more <structname>struct spi_transfer</structname>
 641         objects, each of which wraps a full duplex SPI transfer.
 642         A variety of protocol tweaking options are needed, because
 643         different chips adopt very different policies for how they
 644         use the bits transferred with SPI.
 645   </para>
 646 !Iinclude/linux/spi/spi.h
 647 !Fdrivers/spi/spi.c spi_register_board_info
 648 !Edrivers/spi/spi.c
 649   </chapter>
 650
 651   <chapter id="i2c">
 652      <title>I<superscript>2</superscript>C and SMBus Subsystem</title>
 653
 654      <para>
 655         I<superscript>2</superscript>C (or without fancy typography, "I2C")
 656         is an acronym for the "Inter-IC" bus, a simple bus protocol which is
 657         widely used where low data rate communications suffice.
 658         Since it's also a licensed trademark, some vendors use another
 659         name (such as "Two-Wire Interface", TWI) for the same bus.
 660         I2C only needs two signals (SCL for clock, SDA for data), conserving
 661         board real estate and minimizing signal quality issues.
 662         Most I2C devices use seven bit addresses, and bus speeds of up
 663         to 400 kHz; there's a high speed extension (3.4 MHz) that's not yet
 664         found wide use.
 665         I2C is a multi-master bus; open drain signaling is used to
 666         arbitrate between masters, as well as to handshake and to
 667         synchronize clocks from slower clients.
 668      </para>
 669
 670      <para>
 671         The Linux I2C programming interfaces support only the master
 672         side of bus interactions, not the slave side.
 673         The programming interface is structured around two kinds of driver,
 674         and two kinds of device.
 675         An I2C "Adapter Driver" abstracts the controller hardware; it binds
 676         to a physical device (perhaps a PCI device or platform_device) and
 677         exposes a <structname>struct i2c_adapter</structname> representing
 678         each I2C bus segment it manages.
 679         On each I2C bus segment will be I2C devices represented by a
 680         <structname>struct i2c_client</structname>.  Those devices will
 681         be bound to a <structname>struct i2c_driver</structname>,
 682         which should follow the standard Linux driver model.
 683         (At this writing, a legacy model is more widely used.)
 684         There are functions to perform various I2C protocol operations; at
 685         this writing all such functions are usable only from task context.
 686      </para>
 687
 688      <para>
 689         The System Management Bus (SMBus) is a sibling protocol.  Most SMBus
 690         systems are also I2C conformant.  The electrical constraints are
 691         tighter for SMBus, and it standardizes particular protocol messages
 692         and idioms.  Controllers that support I2C can also support most
 693         SMBus operations, but SMBus controllers don't support all the protocol
 694         options that an I2C controller will.
 695         There are functions to perform various SMBus protocol operations,
 696         either using I2C primitives or by issuing SMBus commands to
 697         i2c_adapter devices which don't support those I2C operations.
 698      </para>
 699
 700 !Iinclude/linux/i2c.h
 701 !Fdrivers/i2c/i2c-boardinfo.c i2c_register_board_info
 702 !Edrivers/i2c/i2c-core.c
 703   </chapter>
 704
 705   <chapter id="splice">
 706       <title>splice API</title>
 707   <para>)
 708         splice is a method for moving blocks of data around inside the
 709         kernel, without continually transferring it between the kernel
 710         and user space.
 711   </para>
 712 !Iinclude/linux/splice.h
 713 !Ffs/splice.c
 714   </chapter>
 715
 716
 717 </book>