Based on kernel version 4.8. Page generated on 2016-10-06 23:15 EST.
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>