Documentation/DocBook/device-drivers.tmpl

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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>

<book id="LinuxDriversAPI">
 <bookinfo>
  <title>Linux Device Drivers</title>

  <legalnotice>
   <para>
     This documentation is free software; you can redistribute
     it and/or modify it under the terms of the GNU General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later
     version.
   </para>

   <para>
     This program is distributed in the hope that it will be
     useful, but WITHOUT ANY WARRANTY; without even the implied
     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
     See the GNU General Public License for more details.
   </para>

   <para>
     You should have received a copy of the GNU General Public
     License along with this program; if not, write to the Free
     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
     MA 02111-1307 USA
   </para>

   <para>
     For more details see the file COPYING in the source
     distribution of Linux.
   </para>
  </legalnotice>
 </bookinfo>

<toc></toc>

  <chapter id="Basics">
     <title>Driver Basics</title>
     <sect1><title>Driver Entry and Exit points</title>
!Iinclude/linux/init.h
     </sect1>

     <sect1><title>Atomic and pointer manipulation</title>
!Iarch/x86/include/asm/atomic.h
     </sect1>

     <sect1><title>Delaying, scheduling, and timer routines</title>
!Iinclude/linux/sched.h
!Ekernel/sched/core.c
!Ikernel/sched/cpupri.c
!Ikernel/sched/fair.c
!Iinclude/linux/completion.h
!Ekernel/time/timer.c
     </sect1>
     <sect1><title>Wait queues and Wake events</title>
!Iinclude/linux/wait.h
!Ekernel/sched/wait.c
     </sect1>
     <sect1><title>High-resolution timers</title>
!Iinclude/linux/ktime.h
!Iinclude/linux/hrtimer.h
!Ekernel/time/hrtimer.c
     </sect1>
     <sect1><title>Workqueues and Kevents</title>
!Iinclude/linux/workqueue.h
!Ekernel/workqueue.c
     </sect1>
     <sect1><title>Internal Functions</title>
!Ikernel/exit.c
!Ikernel/signal.c
!Iinclude/linux/kthread.h
!Ekernel/kthread.c
     </sect1>

     <sect1><title>Kernel objects manipulation</title>
<!--
X!Iinclude/linux/kobject.h
-->
!Elib/kobject.c
     </sect1>

     <sect1><title>Kernel utility functions</title>
!Iinclude/linux/kernel.h
!Ekernel/printk/printk.c
!Ekernel/panic.c
!Ekernel/sys.c
!Ekernel/rcu/srcu.c
!Ekernel/rcu/tree.c
!Ekernel/rcu/tree_plugin.h
!Ekernel/rcu/update.c
     </sect1>

     <sect1><title>Device Resource Management</title>
!Edrivers/base/devres.c
     </sect1>

  </chapter>

  <chapter id="devdrivers">
     <title>Device drivers infrastructure</title>
     <sect1><title>The Basic Device Driver-Model Structures </title>
!Iinclude/linux/device.h
     </sect1>
     <sect1><title>Device Drivers Base</title>
!Idrivers/base/init.c
!Edrivers/base/driver.c
!Edrivers/base/core.c
!Edrivers/base/syscore.c
!Edrivers/base/class.c
!Idrivers/base/node.c
!Edrivers/base/firmware_class.c
!Edrivers/base/transport_class.c
<!-- Cannot be included, because
     attribute_container_add_class_device_adapter
 and attribute_container_classdev_to_container
     exceed allowed 44 characters maximum
X!Edrivers/base/attribute_container.c
-->
!Edrivers/base/dd.c
<!--
X!Edrivers/base/interface.c
-->
!Iinclude/linux/platform_device.h
!Edrivers/base/platform.c
!Edrivers/base/bus.c
     </sect1>
     <sect1><title>Device Drivers DMA Management</title>
!Edrivers/dma-buf/dma-buf.c
!Edrivers/dma-buf/fence.c
!Edrivers/dma-buf/seqno-fence.c
!Iinclude/linux/fence.h
!Iinclude/linux/seqno-fence.h
!Edrivers/dma-buf/reservation.c
!Iinclude/linux/reservation.h
!Edrivers/base/dma-coherent.c
!Edrivers/base/dma-mapping.c
     </sect1>
     <sect1><title>Device Drivers Power Management</title>
!Edrivers/base/power/main.c
     </sect1>
     <sect1><title>Device Drivers ACPI Support</title>
<!-- Internal functions only
X!Edrivers/acpi/sleep/main.c
X!Edrivers/acpi/sleep/wakeup.c
X!Edrivers/acpi/motherboard.c
X!Edrivers/acpi/bus.c
-->
!Edrivers/acpi/scan.c
!Idrivers/acpi/scan.c
<!-- No correct structured comments
X!Edrivers/acpi/pci_bind.c
-->
     </sect1>
     <sect1><title>Device drivers PnP support</title>
!Idrivers/pnp/core.c
<!-- No correct structured comments
X!Edrivers/pnp/system.c
 -->
!Edrivers/pnp/card.c
!Idrivers/pnp/driver.c
!Edrivers/pnp/manager.c
!Edrivers/pnp/support.c
     </sect1>
     <sect1><title>Userspace IO devices</title>
!Edrivers/uio/uio.c
!Iinclude/linux/uio_driver.h
     </sect1>
  </chapter>

  <chapter id="parportdev">
     <title>Parallel Port Devices</title>
!Iinclude/linux/parport.h
!Edrivers/parport/ieee1284.c
!Edrivers/parport/share.c
!Idrivers/parport/daisy.c
  </chapter>

  <chapter id="message_devices">
	<title>Message-based devices</title>
     <sect1><title>Fusion message devices</title>
!Edrivers/message/fusion/mptbase.c
!Idrivers/message/fusion/mptbase.c
!Edrivers/message/fusion/mptscsih.c
!Idrivers/message/fusion/mptscsih.c
!Idrivers/message/fusion/mptctl.c
!Idrivers/message/fusion/mptspi.c
!Idrivers/message/fusion/mptfc.c
!Idrivers/message/fusion/mptlan.c
     </sect1>
  </chapter>

  <chapter id="snddev">
     <title>Sound Devices</title>
!Iinclude/sound/core.h
!Esound/sound_core.c
!Iinclude/sound/pcm.h
!Esound/core/pcm.c
!Esound/core/device.c
!Esound/core/info.c
!Esound/core/rawmidi.c
!Esound/core/sound.c
!Esound/core/memory.c
!Esound/core/pcm_memory.c
!Esound/core/init.c
!Esound/core/isadma.c
!Esound/core/control.c
!Esound/core/pcm_lib.c
!Esound/core/hwdep.c
!Esound/core/pcm_native.c
!Esound/core/memalloc.c
<!-- FIXME: Removed for now since no structured comments in source
X!Isound/sound_firmware.c
-->
  </chapter>

  <chapter id="mediadev">
     <title>Media Devices</title>

     <sect1><title>Video2Linux devices</title>
!Iinclude/media/tuner.h
!Iinclude/media/tuner-types.h
!Iinclude/media/tveeprom.h
!Iinclude/media/v4l2-async.h
!Iinclude/media/v4l2-ctrls.h
!Iinclude/media/v4l2-dv-timings.h
!Iinclude/media/v4l2-event.h
!Iinclude/media/v4l2-flash-led-class.h
!Iinclude/media/v4l2-mediabus.h
!Iinclude/media/v4l2-mem2mem.h
!Iinclude/media/v4l2-of.h
!Iinclude/media/v4l2-subdev.h
!Iinclude/media/videobuf2-core.h
!Iinclude/media/videobuf2-v4l2.h
!Iinclude/media/videobuf2-memops.h
     </sect1>
     <sect1><title>Digital TV (DVB) devices</title>
!Idrivers/media/dvb-core/dvb_ca_en50221.h
!Idrivers/media/dvb-core/dvb_frontend.h
!Idrivers/media/dvb-core/dvb_math.h
!Idrivers/media/dvb-core/dvb_ringbuffer.h
!Idrivers/media/dvb-core/dvbdev.h
	<sect1><title>Digital TV Demux API</title>
	    <para>The kernel demux API defines a driver-internal interface for
	    registering low-level, hardware specific driver to a hardware
	    independent demux layer. It is only of interest for Digital TV
	    device driver writers. The header file for this API is named
	    <constant>demux.h</constant> and located in
	    <constant>drivers/media/dvb-core</constant>.</para>

	<para>The demux API should be implemented for each demux in the
	system. It is used to select the TS source of a demux and to manage
	the demux resources. When the demux client allocates a resource via
	the demux API, it receives a pointer to the API of that
	resource.</para>
	<para>Each demux receives its TS input from a DVB front-end or from
	memory, as set via this demux API. In a system with more than one
	front-end, the API can be used to select one of the DVB front-ends
	as a TS source for a demux, unless this is fixed in the HW platform.
	The demux API only controls front-ends regarding to their connections
	with demuxes; the APIs used to set the other front-end parameters,
	such as tuning, are not defined in this document.</para>
	<para>The functions that implement the abstract interface demux should
	be defined static or module private and registered to the Demux
	core for external access. It is not necessary to implement every
	function in the struct <constant>dmx_demux</constant>. For example,
	a demux interface might support Section filtering, but not PES
	filtering. The API client is expected to check the value of any
	function pointer before calling the function: the value of NULL means
	that the &#8220;function is not available&#8221;.</para>
	<para>Whenever the functions of the demux API modify shared data,
	the possibilities of lost update and race condition problems should
	be addressed, e.g. by protecting parts of code with mutexes.</para>
	<para>Note that functions called from a bottom half context must not
	sleep. Even a simple memory allocation without using GFP_ATOMIC can
	result in a kernel thread being put to sleep if swapping is needed.
	For example, the Linux kernel calls the functions of a network device
	interface from a bottom half context. Thus, if a demux API function
	is called from network device code, the function must not sleep.
	</para>
    </sect1>

    <section id="demux_callback_api">
	<title>Demux Callback API</title>
	<para>This kernel-space API comprises the callback functions that
	deliver filtered data to the demux client. Unlike the other DVB
	kABIs, these functions are provided by the client and called from
	the demux code.</para>
	<para>The function pointers of this abstract interface are not
	packed into a structure as in the other demux APIs, because the
	callback functions are registered and used independent of each
	other. As an example, it is possible for the API client to provide
	several callback functions for receiving TS packets and no
	callbacks for PES packets or sections.</para>
	<para>The functions that implement the callback API need not be
	re-entrant: when a demux driver calls one of these functions,
	the driver is not allowed to call the function again before
	the original call returns. If a callback is triggered by a
	hardware interrupt, it is recommended to use the Linux
	&#8220;bottom half&#8221; mechanism or start a tasklet instead of
	making the callback function call directly from a hardware
	interrupt.</para>
	<para>This mechanism is implemented by
	<link linkend='API-dmx-ts-cb'>dmx_ts_cb()</link> and
	<link linkend='API-dmx-section-cb'>dmx_section_cb()</link>.</para>
    </section>

!Idrivers/media/dvb-core/demux.h
    </sect1>
    <sect1><title>Remote Controller devices</title>
!Iinclude/media/rc-core.h
!Iinclude/media/lirc_dev.h
    </sect1>
    <sect1><title>Media Controller devices</title>
!Iinclude/media/media-device.h
!Iinclude/media/media-devnode.h
!Iinclude/media/media-entity.h
    </sect1>

  </chapter>

  <chapter id="uart16x50">
     <title>16x50 UART Driver</title>
!Edrivers/tty/serial/serial_core.c
!Edrivers/tty/serial/8250/8250_core.c
  </chapter>

  <chapter id="fbdev">
     <title>Frame Buffer Library</title>

     <para>
       The frame buffer drivers depend heavily on four data structures.
       These structures are declared in include/linux/fb.h.  They are
       fb_info, fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs.
       The last three can be made available to and from userland.
     </para>

     <para>
       fb_info defines the current state of a particular video card.
       Inside fb_info, there exists a fb_ops structure which is a
       collection of needed functions to make fbdev and fbcon work.
       fb_info is only visible to the kernel.
     </para>

     <para>
       fb_var_screeninfo is used to describe the features of a video card
       that are user defined.  With fb_var_screeninfo, things such as
       depth and the resolution may be defined.
     </para>

     <para>
       The next structure is fb_fix_screeninfo. This defines the
       properties of a card that are created when a mode is set and can't
       be changed otherwise.  A good example of this is the start of the
       frame buffer memory.  This "locks" the address of the frame buffer
       memory, so that it cannot be changed or moved.
     </para>

     <para>
       The last structure is fb_monospecs. In the old API, there was
       little importance for fb_monospecs. This allowed for forbidden things
       such as setting a mode of 800x600 on a fix frequency monitor. With
       the new API, fb_monospecs prevents such things, and if used
       correctly, can prevent a monitor from being cooked.  fb_monospecs
       will not be useful until kernels 2.5.x.
     </para>

     <sect1><title>Frame Buffer Memory</title>
!Edrivers/video/fbdev/core/fbmem.c
     </sect1>
<!--
     <sect1><title>Frame Buffer Console</title>
X!Edrivers/video/console/fbcon.c
     </sect1>
-->
     <sect1><title>Frame Buffer Colormap</title>
!Edrivers/video/fbdev/core/fbcmap.c
     </sect1>
<!-- FIXME:
  drivers/video/fbgen.c has no docs, which stuffs up the sgml.  Comment
  out until somebody adds docs.  KAO
     <sect1><title>Frame Buffer Generic Functions</title>
X!Idrivers/video/fbgen.c
     </sect1>
KAO -->
     <sect1><title>Frame Buffer Video Mode Database</title>
!Idrivers/video/fbdev/core/modedb.c
!Edrivers/video/fbdev/core/modedb.c
     </sect1>
     <sect1><title>Frame Buffer Macintosh Video Mode Database</title>
!Edrivers/video/fbdev/macmodes.c
     </sect1>
     <sect1><title>Frame Buffer Fonts</title>
        <para>
           Refer to the file lib/fonts/fonts.c for more information.
        </para>
<!-- FIXME: Removed for now since no structured comments in source
X!Ilib/fonts/fonts.c
-->
     </sect1>
  </chapter>

  <chapter id="input_subsystem">
     <title>Input Subsystem</title>
     <sect1><title>Input core</title>
!Iinclude/linux/input.h
!Edrivers/input/input.c
!Edrivers/input/ff-core.c
!Edrivers/input/ff-memless.c
     </sect1>
     <sect1><title>Multitouch Library</title>
!Iinclude/linux/input/mt.h
!Edrivers/input/input-mt.c
     </sect1>
     <sect1><title>Polled input devices</title>
!Iinclude/linux/input-polldev.h
!Edrivers/input/input-polldev.c
     </sect1>
     <sect1><title>Matrix keyboars/keypads</title>
!Iinclude/linux/input/matrix_keypad.h
     </sect1>
     <sect1><title>Sparse keymap support</title>
!Iinclude/linux/input/sparse-keymap.h
!Edrivers/input/sparse-keymap.c
     </sect1>
  </chapter>

  <chapter id="spi">
      <title>Serial Peripheral Interface (SPI)</title>
  <para>
	SPI is the "Serial Peripheral Interface", widely used with
	embedded systems because it is a simple and efficient
	interface:  basically a multiplexed shift register.
	Its three signal wires hold a clock (SCK, often in the range
	of 1-20 MHz), a "Master Out, Slave In" (MOSI) data line, and
	a "Master In, Slave Out" (MISO) data line.
	SPI is a full duplex protocol; for each bit shifted out the
	MOSI line (one per clock) another is shifted in on the MISO line.
	Those bits are assembled into words of various sizes on the
	way to and from system memory.
	An additional chipselect line is usually active-low (nCS);
	four signals are normally used for each peripheral, plus
	sometimes an interrupt.
  </para>
  <para>
	The SPI bus facilities listed here provide a generalized
	interface to declare SPI busses and devices, manage them
	according to the standard Linux driver model, and perform
	input/output operations.
	At this time, only "master" side interfaces are supported,
	where Linux talks to SPI peripherals and does not implement
	such a peripheral itself.
	(Interfaces to support implementing SPI slaves would
	necessarily look different.)
  </para>
  <para>
	The programming interface is structured around two kinds of driver,
	and two kinds of device.
	A "Controller Driver" abstracts the controller hardware, which may
	be as simple as a set of GPIO pins or as complex as a pair of FIFOs
	connected to dual DMA engines on the other side of the SPI shift
	register (maximizing throughput).  Such drivers bridge between
	whatever bus they sit on (often the platform bus) and SPI, and
	expose the SPI side of their device as a
	<structname>struct spi_master</structname>.
	SPI devices are children of that master, represented as a
	<structname>struct spi_device</structname> and manufactured from
	<structname>struct spi_board_info</structname> descriptors which
	are usually provided by board-specific initialization code.
	A <structname>struct spi_driver</structname> is called a
	"Protocol Driver", and is bound to a spi_device using normal
	driver model calls.
  </para>
  <para>
	The I/O model is a set of queued messages.  Protocol drivers
	submit one or more <structname>struct spi_message</structname>
	objects, which are processed and completed asynchronously.
	(There are synchronous wrappers, however.)  Messages are
	built from one or more <structname>struct spi_transfer</structname>
	objects, each of which wraps a full duplex SPI transfer.
	A variety of protocol tweaking options are needed, because
	different chips adopt very different policies for how they
	use the bits transferred with SPI.
  </para>
!Iinclude/linux/spi/spi.h
!Fdrivers/spi/spi.c spi_register_board_info
!Edrivers/spi/spi.c
  </chapter>

  <chapter id="i2c">
     <title>I<superscript>2</superscript>C and SMBus Subsystem</title>

     <para>
	I<superscript>2</superscript>C (or without fancy typography, "I2C")
	is an acronym for the "Inter-IC" bus, a simple bus protocol which is
	widely used where low data rate communications suffice.
	Since it's also a licensed trademark, some vendors use another
	name (such as "Two-Wire Interface", TWI) for the same bus.
	I2C only needs two signals (SCL for clock, SDA for data), conserving
	board real estate and minimizing signal quality issues.
	Most I2C devices use seven bit addresses, and bus speeds of up
	to 400 kHz; there's a high speed extension (3.4 MHz) that's not yet
	found wide use.
	I2C is a multi-master bus; open drain signaling is used to
	arbitrate between masters, as well as to handshake and to
	synchronize clocks from slower clients.
     </para>

     <para>
	The Linux I2C programming interfaces support only the master
	side of bus interactions, not the slave side.
	The programming interface is structured around two kinds of driver,
	and two kinds of device.
	An I2C "Adapter Driver" abstracts the controller hardware; it binds
	to a physical device (perhaps a PCI device or platform_device) and
	exposes a <structname>struct i2c_adapter</structname> representing
	each I2C bus segment it manages.
	On each I2C bus segment will be I2C devices represented by a
	<structname>struct i2c_client</structname>.  Those devices will
	be bound to a <structname>struct i2c_driver</structname>,
	which should follow the standard Linux driver model.
	(At this writing, a legacy model is more widely used.)
	There are functions to perform various I2C protocol operations; at
	this writing all such functions are usable only from task context.
     </para>

     <para>
	The System Management Bus (SMBus) is a sibling protocol.  Most SMBus
	systems are also I2C conformant.  The electrical constraints are
	tighter for SMBus, and it standardizes particular protocol messages
	and idioms.  Controllers that support I2C can also support most
	SMBus operations, but SMBus controllers don't support all the protocol
	options that an I2C controller will.
	There are functions to perform various SMBus protocol operations,
	either using I2C primitives or by issuing SMBus commands to
	i2c_adapter devices which don't support those I2C operations.
     </para>

!Iinclude/linux/i2c.h
!Fdrivers/i2c/i2c-boardinfo.c i2c_register_board_info
!Edrivers/i2c/i2c-core.c
  </chapter>

  <chapter id="hsi">
     <title>High Speed Synchronous Serial Interface (HSI)</title>

     <para>
	High Speed Synchronous Serial Interface (HSI) is a
	serial interface mainly used for connecting application
	engines (APE) with cellular modem engines (CMT) in cellular
	handsets.

	HSI provides multiplexing for up to 16 logical channels,
	low-latency and full duplex communication.
     </para>

!Iinclude/linux/hsi/hsi.h
!Edrivers/hsi/hsi.c
  </chapter>

  <chapter id="pwm">
    <title>Pulse-Width Modulation (PWM)</title>
    <para>
      Pulse-width modulation is a modulation technique primarily used to
      control power supplied to electrical devices.
    </para>
    <para>
      The PWM framework provides an abstraction for providers and consumers
      of PWM signals. A controller that provides one or more PWM signals is
      registered as <structname>struct pwm_chip</structname>. Providers are
      expected to embed this structure in a driver-specific structure. This
      structure contains fields that describe a particular chip.
    </para>
    <para>
      A chip exposes one or more PWM signal sources, each of which exposed
      as a <structname>struct pwm_device</structname>. Operations can be
      performed on PWM devices to control the period, duty cycle, polarity
      and active state of the signal.
    </para>
    <para>
      Note that PWM devices are exclusive resources: they can always only be
      used by one consumer at a time.
    </para>
!Iinclude/linux/pwm.h
!Edrivers/pwm/core.c
  </chapter>

</book>