diff options
| author | Jonathan Corbet <corbet@lwn.net> | 2016-08-20 15:02:50 -0400 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2016-08-22 16:11:22 -0400 |
| commit | 47cb398dd75a9faa89d0617b55d4cf537935b731 (patch) | |
| tree | 12ff5f67133219fcf86b6e1166a14e25838346da /Documentation/DocBook | |
| parent | 5512128f027aec63a9a2ca792858801554a57baf (diff) | |
Docs: sphinxify device-drivers.tmpl
Perform a basic sphinx conversion of the device-drivers docbook and move it
to its own directory.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/Makefile | 2 | ||||
| -rw-r--r-- | Documentation/DocBook/device-drivers.tmpl | 521 |
2 files changed, 1 insertions, 522 deletions
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index a91c96522379..5fbfb7273f38 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile | |||
| @@ -6,7 +6,7 @@ | |||
| 6 | # To add a new book the only step required is to add the book to the | 6 | # To add a new book the only step required is to add the book to the |
| 7 | # list of DOCBOOKS. | 7 | # list of DOCBOOKS. |
| 8 | 8 | ||
| 9 | DOCBOOKS := z8530book.xml device-drivers.xml \ | 9 | DOCBOOKS := z8530book.xml \ |
| 10 | kernel-hacking.xml kernel-locking.xml deviceiobook.xml \ | 10 | kernel-hacking.xml kernel-locking.xml deviceiobook.xml \ |
| 11 | writing_usb_driver.xml networking.xml \ | 11 | writing_usb_driver.xml networking.xml \ |
| 12 | kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \ | 12 | kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \ |
diff --git a/Documentation/DocBook/device-drivers.tmpl b/Documentation/DocBook/device-drivers.tmpl deleted file mode 100644 index 9c10030eb2be..000000000000 --- a/Documentation/DocBook/device-drivers.tmpl +++ /dev/null | |||
| @@ -1,521 +0,0 @@ | |||
| 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> | ||
