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-x86/atomic_32.h
  49 !Iinclude/asm-x86/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-x86/bitops_32.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-x86/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/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 !Enet/sched/sch_generic.c
 244 !Iinclude/linux/etherdevice.h
 245 !Iinclude/linux/netdevice.h
 246      </sect1>
 247      <sect1><title>PHY Support</title>
 248 !Edrivers/net/phy/phy.c
 249 !Idrivers/net/phy/phy.c
 250 !Edrivers/net/phy/phy_device.c
 251 !Idrivers/net/phy/phy_device.c
 252 !Edrivers/net/phy/mdio_bus.c
 253 !Idrivers/net/phy/mdio_bus.c
 254      </sect1>
 255 <!-- FIXME: Removed for now since no structured comments in source
 256      <sect1><title>Wireless</title>
 257 X!Enet/core/wireless.c
 258      </sect1>
 259 -->
 260      <sect1><title>Synchronous PPP</title>
 261 !Edrivers/net/wan/syncppp.c
 262      </sect1>
 263   </chapter>
 264
 265   <chapter id="modload">
 266      <title>Module Support</title>
 267      <sect1><title>Module Loading</title>
 268 !Ekernel/kmod.c
 269      </sect1>
 270      <sect1><title>Inter Module support</title>
 271         <para>
 272            Refer to the file kernel/module.c for more information.
 273         </para>
 274 <!-- FIXME: Removed for now since no structured comments in source
 275 X!Ekernel/module.c
 276 -->
 277      </sect1>
 278   </chapter>
 279
 280   <chapter id="hardware">
 281      <title>Hardware Interfaces</title>
 282      <sect1><title>Interrupt Handling</title>
 283 !Ekernel/irq/manage.c
 284      </sect1>
 285
 286      <sect1><title>DMA Channels</title>
 287 !Ekernel/dma.c
 288      </sect1>
 289
 290      <sect1><title>Resources Management</title>
 291 !Ikernel/resource.c
 292 !Ekernel/resource.c
 293      </sect1>
 294
 295      <sect1><title>MTRR Handling</title>
 296 !Earch/x86/kernel/cpu/mtrr/main.c
 297      </sect1>
 298
 299      <sect1><title>PCI Support Library</title>
 300 !Edrivers/pci/pci.c
 301 !Edrivers/pci/pci-driver.c
 302 !Edrivers/pci/remove.c
 303 !Edrivers/pci/pci-acpi.c
 304 !Edrivers/pci/search.c
 305 !Edrivers/pci/msi.c
 306 !Edrivers/pci/bus.c
 307 <!-- FIXME: Removed for now since no structured comments in source
 308 X!Edrivers/pci/hotplug.c
 309 -->
 310 !Edrivers/pci/probe.c
 311 !Edrivers/pci/rom.c
 312      </sect1>
 313      <sect1><title>PCI Hotplug Support Library</title>
 314 !Edrivers/pci/hotplug/pci_hotplug_core.c
 315      </sect1>
 316      <sect1><title>MCA Architecture</title>
 317         <sect2><title>MCA Device Functions</title>
 318            <para>
 319               Refer to the file arch/x86/kernel/mca_32.c for more information.
 320            </para>
 321 <!-- FIXME: Removed for now since no structured comments in source
 322 X!Earch/x86/kernel/mca_32.c
 323 -->
 324         </sect2>
 325         <sect2><title>MCA Bus DMA</title>
 326 !Iinclude/asm-x86/mca_dma.h
 327         </sect2>
 328      </sect1>
 329   </chapter>
 330
 331   <chapter id="firmware">
 332      <title>Firmware Interfaces</title>
 333      <sect1><title>DMI Interfaces</title>
 334 !Edrivers/firmware/dmi_scan.c
 335      </sect1>
 336      <sect1><title>EDD Interfaces</title>
 337 !Idrivers/firmware/edd.c
 338      </sect1>
 339   </chapter>
 340
 341   <chapter id="security">
 342      <title>Security Framework</title>
 343 !Isecurity/security.c
 344   </chapter>
 345
 346   <chapter id="audit">
 347      <title>Audit Interfaces</title>
 348 !Ekernel/audit.c
 349 !Ikernel/auditsc.c
 350 !Ikernel/auditfilter.c
 351   </chapter>
 352
 353   <chapter id="accounting">
 354      <title>Accounting Framework</title>
 355 !Ikernel/acct.c
 356   </chapter>
 357
 358   <chapter id="pmfuncs">
 359      <title>Power Management</title>
 360 !Ekernel/power/pm.c
 361   </chapter>
 362
 363   <chapter id="devdrivers">
 364      <title>Device drivers infrastructure</title>
 365      <sect1><title>Device Drivers Base</title>
 366 <!--
 367 X!Iinclude/linux/device.h
 368 -->
 369 !Edrivers/base/driver.c
 370 !Edrivers/base/core.c
 371 !Edrivers/base/class.c
 372 !Edrivers/base/firmware_class.c
 373 !Edrivers/base/transport_class.c
 374 !Edrivers/base/dmapool.c
 375 <!-- Cannot be included, because
 376      attribute_container_add_class_device_adapter
 377  and attribute_container_classdev_to_container
 378      exceed allowed 44 characters maximum
 379 X!Edrivers/base/attribute_container.c
 380 -->
 381 !Edrivers/base/sys.c
 382 <!--
 383 X!Edrivers/base/interface.c
 384 -->
 385 !Edrivers/base/platform.c
 386 !Edrivers/base/bus.c
 387      </sect1>
 388      <sect1><title>Device Drivers Power Management</title>
 389 !Edrivers/base/power/main.c
 390      </sect1>
 391      <sect1><title>Device Drivers ACPI Support</title>
 392 <!-- Internal functions only
 393 X!Edrivers/acpi/sleep/main.c
 394 X!Edrivers/acpi/sleep/wakeup.c
 395 X!Edrivers/acpi/motherboard.c
 396 X!Edrivers/acpi/bus.c
 397 -->
 398 !Edrivers/acpi/scan.c
 399 !Idrivers/acpi/scan.c
 400 <!-- No correct structured comments
 401 X!Edrivers/acpi/pci_bind.c
 402 -->
 403      </sect1>
 404      <sect1><title>Device drivers PnP support</title>
 405 !Idrivers/pnp/core.c
 406 <!-- No correct structured comments
 407 X!Edrivers/pnp/system.c
 408  -->
 409 !Edrivers/pnp/card.c
 410 !Idrivers/pnp/driver.c
 411 !Edrivers/pnp/manager.c
 412 !Edrivers/pnp/support.c
 413      </sect1>
 414      <sect1><title>Userspace IO devices</title>
 415 !Edrivers/uio/uio.c
 416 !Iinclude/linux/uio_driver.h
 417      </sect1>
 418   </chapter>
 419
 420   <chapter id="blkdev">
 421      <title>Block Devices</title>
 422 !Eblock/blk-core.c
 423 !Eblock/blk-map.c
 424 !Iblock/blk-sysfs.c
 425 !Eblock/blk-settings.c
 426 !Eblock/blk-exec.c
 427 !Eblock/blk-barrier.c
 428 !Eblock/blk-tag.c
 429   </chapter>
 430
 431   <chapter id="chrdev">
 432         <title>Char devices</title>
 433 !Efs/char_dev.c
 434   </chapter>
 435
 436   <chapter id="miscdev">
 437      <title>Miscellaneous Devices</title>
 438 !Edrivers/char/misc.c
 439   </chapter>
 440
 441   <chapter id="parportdev">
 442      <title>Parallel Port Devices</title>
 443 !Iinclude/linux/parport.h
 444 !Edrivers/parport/ieee1284.c
 445 !Edrivers/parport/share.c
 446 !Idrivers/parport/daisy.c
 447   </chapter>
 448
 449   <chapter id="message_devices">
 450         <title>Message-based devices</title>
 451      <sect1><title>Fusion message devices</title>
 452 !Edrivers/message/fusion/mptbase.c
 453 !Idrivers/message/fusion/mptbase.c
 454 !Edrivers/message/fusion/mptscsih.c
 455 !Idrivers/message/fusion/mptscsih.c
 456 !Idrivers/message/fusion/mptctl.c
 457 !Idrivers/message/fusion/mptspi.c
 458 !Idrivers/message/fusion/mptfc.c
 459 !Idrivers/message/fusion/mptlan.c
 460      </sect1>
 461      <sect1><title>I2O message devices</title>
 462 !Iinclude/linux/i2o.h
 463 !Idrivers/message/i2o/core.h
 464 !Edrivers/message/i2o/iop.c
 465 !Idrivers/message/i2o/iop.c
 466 !Idrivers/message/i2o/config-osm.c
 467 !Edrivers/message/i2o/exec-osm.c
 468 !Idrivers/message/i2o/exec-osm.c
 469 !Idrivers/message/i2o/bus-osm.c
 470 !Edrivers/message/i2o/device.c
 471 !Idrivers/message/i2o/device.c
 472 !Idrivers/message/i2o/driver.c
 473 !Idrivers/message/i2o/pci.c
 474 !Idrivers/message/i2o/i2o_block.c
 475 !Idrivers/message/i2o/i2o_scsi.c
 476 !Idrivers/message/i2o/i2o_proc.c
 477      </sect1>
 478   </chapter>
 479
 480   <chapter id="snddev">
 481      <title>Sound Devices</title>
 482 !Iinclude/sound/core.h
 483 !Esound/sound_core.c
 484 !Iinclude/sound/pcm.h
 485 !Esound/core/pcm.c
 486 !Esound/core/device.c
 487 !Esound/core/info.c
 488 !Esound/core/rawmidi.c
 489 !Esound/core/sound.c
 490 !Esound/core/memory.c
 491 !Esound/core/pcm_memory.c
 492 !Esound/core/init.c
 493 !Esound/core/isadma.c
 494 !Esound/core/control.c
 495 !Esound/core/pcm_lib.c
 496 !Esound/core/hwdep.c
 497 !Esound/core/pcm_native.c
 498 !Esound/core/memalloc.c
 499 <!-- FIXME: Removed for now since no structured comments in source
 500 X!Isound/sound_firmware.c
 501 -->
 502   </chapter>
 503
 504   <chapter id="uart16x50">
 505      <title>16x50 UART Driver</title>
 506 !Iinclude/linux/serial_core.h
 507 !Edrivers/serial/serial_core.c
 508 !Edrivers/serial/8250.c
 509   </chapter>
 510
 511   <chapter id="z85230">
 512      <title>Z85230 Support Library</title>
 513 !Edrivers/net/wan/z85230.c
 514   </chapter>
 515
 516   <chapter id="fbdev">
 517      <title>Frame Buffer Library</title>
 518
 519      <para>
 520        The frame buffer drivers depend heavily on four data structures.
 521        These structures are declared in include/linux/fb.h.  They are
 522        fb_info, fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs.
 523        The last three can be made available to and from userland.
 524      </para>
 525
 526      <para>
 527        fb_info defines the current state of a particular video card.
 528        Inside fb_info, there exists a fb_ops structure which is a
 529        collection of needed functions to make fbdev and fbcon work.
 530        fb_info is only visible to the kernel.
 531      </para>
 532
 533      <para>
 534        fb_var_screeninfo is used to describe the features of a video card
 535        that are user defined.  With fb_var_screeninfo, things such as
 536        depth and the resolution may be defined.
 537      </para>
 538
 539      <para>
 540        The next structure is fb_fix_screeninfo. This defines the
 541        properties of a card that are created when a mode is set and can't
 542        be changed otherwise.  A good example of this is the start of the
 543        frame buffer memory.  This "locks" the address of the frame buffer
 544        memory, so that it cannot be changed or moved.
 545      </para>
 546
 547      <para>
 548        The last structure is fb_monospecs. In the old API, there was
 549        little importance for fb_monospecs. This allowed for forbidden things
 550        such as setting a mode of 800x600 on a fix frequency monitor. With
 551        the new API, fb_monospecs prevents such things, and if used
 552        correctly, can prevent a monitor from being cooked.  fb_monospecs
 553        will not be useful until kernels 2.5.x.
 554      </para>
 555
 556      <sect1><title>Frame Buffer Memory</title>
 557 !Edrivers/video/fbmem.c
 558      </sect1>
 559 <!--
 560      <sect1><title>Frame Buffer Console</title>
 561 X!Edrivers/video/console/fbcon.c
 562      </sect1>
 563 -->
 564      <sect1><title>Frame Buffer Colormap</title>
 565 !Edrivers/video/fbcmap.c
 566      </sect1>
 567 <!-- FIXME:
 568   drivers/video/fbgen.c has no docs, which stuffs up the sgml.  Comment
 569   out until somebody adds docs.  KAO
 570      <sect1><title>Frame Buffer Generic Functions</title>
 571 X!Idrivers/video/fbgen.c
 572      </sect1>
 573 KAO -->
 574      <sect1><title>Frame Buffer Video Mode Database</title>
 575 !Idrivers/video/modedb.c
 576 !Edrivers/video/modedb.c
 577      </sect1>
 578      <sect1><title>Frame Buffer Macintosh Video Mode Database</title>
 579 !Edrivers/video/macmodes.c
 580      </sect1>
 581      <sect1><title>Frame Buffer Fonts</title>
 582         <para>
 583            Refer to the file drivers/video/console/fonts.c for more information.
 584         </para>
 585 <!-- FIXME: Removed for now since no structured comments in source
 586 X!Idrivers/video/console/fonts.c
 587 -->
 588      </sect1>
 589   </chapter>
 590
 591   <chapter id="input_subsystem">
 592      <title>Input Subsystem</title>
 593 !Iinclude/linux/input.h
 594 !Edrivers/input/input.c
 595 !Edrivers/input/ff-core.c
 596 !Edrivers/input/ff-memless.c
 597   </chapter>
 598
 599   <chapter id="spi">
 600       <title>Serial Peripheral Interface (SPI)</title>
 601   <para>
 602         SPI is the "Serial Peripheral Interface", widely used with
 603         embedded systems because it is a simple and efficient
 604         interface:  basically a multiplexed shift register.
 605         Its three signal wires hold a clock (SCK, often in the range
 606         of 1-20 MHz), a "Master Out, Slave In" (MOSI) data line, and
 607         a "Master In, Slave Out" (MISO) data line.
 608         SPI is a full duplex protocol; for each bit shifted out the
 609         MOSI line (one per clock) another is shifted in on the MISO line.
 610         Those bits are assembled into words of various sizes on the
 611         way to and from system memory.
 612         An additional chipselect line is usually active-low (nCS);
 613         four signals are normally used for each peripheral, plus
 614         sometimes an interrupt.
 615   </para>
 616   <para>
 617         The SPI bus facilities listed here provide a generalized
 618         interface to declare SPI busses and devices, manage them
 619         according to the standard Linux driver model, and perform
 620         input/output operations.
 621         At this time, only "master" side interfaces are supported,
 622         where Linux talks to SPI peripherals and does not implement
 623         such a peripheral itself.
 624         (Interfaces to support implementing SPI slaves would
 625         necessarily look different.)
 626   </para>
 627   <para>
 628         The programming interface is structured around two kinds of driver,
 629         and two kinds of device.
 630         A "Controller Driver" abstracts the controller hardware, which may
 631         be as simple as a set of GPIO pins or as complex as a pair of FIFOs
 632         connected to dual DMA engines on the other side of the SPI shift
 633         register (maximizing throughput).  Such drivers bridge between
 634         whatever bus they sit on (often the platform bus) and SPI, and
 635         expose the SPI side of their device as a
 636         <structname>struct spi_master</structname>.
 637         SPI devices are children of that master, represented as a
 638         <structname>struct spi_device</structname> and manufactured from
 639         <structname>struct spi_board_info</structname> descriptors which
 640         are usually provided by board-specific initialization code.
 641         A <structname>struct spi_driver</structname> is called a
 642         "Protocol Driver", and is bound to a spi_device using normal
 643         driver model calls.
 644   </para>
 645   <para>
 646         The I/O model is a set of queued messages.  Protocol drivers
 647         submit one or more <structname>struct spi_message</structname>
 648         objects, which are processed and completed asynchronously.
 649         (There are synchronous wrappers, however.)  Messages are
 650         built from one or more <structname>struct spi_transfer</structname>
 651         objects, each of which wraps a full duplex SPI transfer.
 652         A variety of protocol tweaking options are needed, because
 653         different chips adopt very different policies for how they
 654         use the bits transferred with SPI.
 655   </para>
 656 !Iinclude/linux/spi/spi.h
 657 !Fdrivers/spi/spi.c spi_register_board_info
 658 !Edrivers/spi/spi.c
 659   </chapter>
 660
 661   <chapter id="i2c">
 662      <title>I<superscript>2</superscript>C and SMBus Subsystem</title>
 663
 664      <para>
 665         I<superscript>2</superscript>C (or without fancy typography, "I2C")
 666         is an acronym for the "Inter-IC" bus, a simple bus protocol which is
 667         widely used where low data rate communications suffice.
 668         Since it's also a licensed trademark, some vendors use another
 669         name (such as "Two-Wire Interface", TWI) for the same bus.
 670         I2C only needs two signals (SCL for clock, SDA for data), conserving
 671         board real estate and minimizing signal quality issues.
 672         Most I2C devices use seven bit addresses, and bus speeds of up
 673         to 400 kHz; there's a high speed extension (3.4 MHz) that's not yet
 674         found wide use.
 675         I2C is a multi-master bus; open drain signaling is used to
 676         arbitrate between masters, as well as to handshake and to
 677         synchronize clocks from slower clients.
 678      </para>
 679
 680      <para>
 681         The Linux I2C programming interfaces support only the master
 682         side of bus interactions, not the slave side.
 683         The programming interface is structured around two kinds of driver,
 684         and two kinds of device.
 685         An I2C "Adapter Driver" abstracts the controller hardware; it binds
 686         to a physical device (perhaps a PCI device or platform_device) and
 687         exposes a <structname>struct i2c_adapter</structname> representing
 688         each I2C bus segment it manages.
 689         On each I2C bus segment will be I2C devices represented by a
 690         <structname>struct i2c_client</structname>.  Those devices will
 691         be bound to a <structname>struct i2c_driver</structname>,
 692         which should follow the standard Linux driver model.
 693         (At this writing, a legacy model is more widely used.)
 694         There are functions to perform various I2C protocol operations; at
 695         this writing all such functions are usable only from task context.
 696      </para>
 697
 698      <para>
 699         The System Management Bus (SMBus) is a sibling protocol.  Most SMBus
 700         systems are also I2C conformant.  The electrical constraints are
 701         tighter for SMBus, and it standardizes particular protocol messages
 702         and idioms.  Controllers that support I2C can also support most
 703         SMBus operations, but SMBus controllers don't support all the protocol
 704         options that an I2C controller will.
 705         There are functions to perform various SMBus protocol operations,
 706         either using I2C primitives or by issuing SMBus commands to
 707         i2c_adapter devices which don't support those I2C operations.
 708      </para>
 709
 710 !Iinclude/linux/i2c.h
 711 !Fdrivers/i2c/i2c-boardinfo.c i2c_register_board_info
 712 !Edrivers/i2c/i2c-core.c
 713   </chapter>
 714
 715   <chapter id="splice">
 716       <title>splice API</title>
 717   <para>
 718         splice is a method for moving blocks of data around inside the
 719         kernel, without continually transferring them between the kernel
 720         and user space.
 721   </para>
 722 !Ffs/splice.c
 723   </chapter>
 724
 725   <chapter id="pipes">
 726       <title>pipes API</title>
 727   <para>
 728         Pipe interfaces are all for in-kernel (builtin image) use.
 729         They are not exported for use by modules.
 730   </para>
 731 !Iinclude/linux/pipe_fs_i.h
 732 !Ffs/pipe.c
 733   </chapter>
 734
 735 </book>