Commit fd5d2b83 authored by Jonathan Corbet's avatar Jonathan Corbet
Browse files

Merge branch 'driver-api' into doc/4.9 

This short series convers device-drivers.tmpl into the RST format, splits
it up, and sets up the result under Documentation/driver-api/.  For added
fun, I've taken one top-level file (hsi.txt) and folded it into the
document as a way of showing the direction I'm thinking I would like things
to go.  There is plenty more of this sort of work that could be done, to
say the least - this is just a beginning!

The formatted results can be seen at:

    http://static.lwn.net/kerneldoc/driver-api/index.html

As part of the long-term task to turn Documentation/ into less of a horror
movie, I'd like to collect documentation of the driver-specific API here.
Arguably gpu/ and the media API stuff should eventually move here, though
we can discuss the color of that particular shed some other day.
Meanwhile, I'd appreciate comments on the general idea.
parents 829f4c36 d36bbab6

Documentation/DocBook/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -6,7 +6,7 @@ 
# To add a new book the only step required is to add the book to the

# list of DOCBOOKS.



DOCBOOKS := z8530book.xml device-drivers.xml \

DOCBOOKS := z8530book.xml  \

	    kernel-hacking.xml kernel-locking.xml deviceiobook.xml \

	    writing_usb_driver.xml networking.xml \

	    kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \

Documentation/DocBook/device-drivers.tmpl

deleted100644 → 0
+0 −521
Original line number Diff line number Diff line 
<?xml version="1.0" encoding="UTF-8"?>

<!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>Buffer Sharing and Synchronization</title>

       <para>

         The dma-buf subsystem provides the framework for sharing buffers

         for hardware (DMA) access across multiple device drivers and

         subsystems, and for synchronizing asynchronous hardware access.

       </para>

       <para>

         This is used, for example, by drm "prime" multi-GPU support, but

         is of course not limited to GPU use cases.

       </para>

       <para>

         The three main components of this are: (1) dma-buf, representing

         a sg_table and exposed to userspace as a file descriptor to allow

         passing between devices, (2) fence, which provides a mechanism

         to signal when one device as finished access, and (3) reservation,

         which manages the shared or exclusive fence(s) associated with

         the buffer.

       </para>

       <sect2><title>dma-buf</title>

!Edrivers/dma-buf/dma-buf.c

!Iinclude/linux/dma-buf.h

       </sect2>

       <sect2><title>reservation</title>

!Pdrivers/dma-buf/reservation.c Reservation Object Overview

!Edrivers/dma-buf/reservation.c

!Iinclude/linux/reservation.h

       </sect2>

       <sect2><title>fence</title>

!Edrivers/dma-buf/fence.c

!Iinclude/linux/fence.h

!Edrivers/dma-buf/seqno-fence.c

!Iinclude/linux/seqno-fence.h

!Edrivers/dma-buf/fence-array.c

!Iinclude/linux/fence-array.h

!Edrivers/dma-buf/reservation.c

!Iinclude/linux/reservation.h

!Edrivers/dma-buf/sync_file.c

!Iinclude/linux/sync_file.h

       </sect2>

     </sect1>

     <sect1><title>Device Drivers DMA Management</title>

!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="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 keyboards/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_core.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>

Documentation/driver-api/basics.rst

0 → 100644
+120 −0
Original line number Diff line number Diff line 
Driver Basics

=============



Driver Entry and Exit points

----------------------------



.. kernel-doc:: include/linux/init.h

   :internal:



Atomic and pointer manipulation

-------------------------------



.. kernel-doc:: arch/x86/include/asm/atomic.h

   :internal:



Delaying, scheduling, and timer routines

----------------------------------------



.. kernel-doc:: include/linux/sched.h

   :internal:



.. kernel-doc:: kernel/sched/core.c

   :export:



.. kernel-doc:: kernel/sched/cpupri.c

   :internal:



.. kernel-doc:: kernel/sched/fair.c

   :internal:



.. kernel-doc:: include/linux/completion.h

   :internal:



.. kernel-doc:: kernel/time/timer.c

   :export:



Wait queues and Wake events

---------------------------



.. kernel-doc:: include/linux/wait.h

   :internal:



.. kernel-doc:: kernel/sched/wait.c

   :export:



High-resolution timers

----------------------



.. kernel-doc:: include/linux/ktime.h

   :internal:



.. kernel-doc:: include/linux/hrtimer.h

   :internal:



.. kernel-doc:: kernel/time/hrtimer.c

   :export:



Workqueues and Kevents

----------------------



.. kernel-doc:: include/linux/workqueue.h

   :internal:



.. kernel-doc:: kernel/workqueue.c

   :export:



Internal Functions

------------------



.. kernel-doc:: kernel/exit.c

   :internal:



.. kernel-doc:: kernel/signal.c

   :internal:



.. kernel-doc:: include/linux/kthread.h

   :internal:



.. kernel-doc:: kernel/kthread.c

   :export:



Kernel objects manipulation

---------------------------



.. kernel-doc:: lib/kobject.c

   :export:



Kernel utility functions

------------------------



.. kernel-doc:: include/linux/kernel.h

   :internal:



.. kernel-doc:: kernel/printk/printk.c

   :export:



.. kernel-doc:: kernel/panic.c

   :export:



.. kernel-doc:: kernel/sys.c

   :export:



.. kernel-doc:: kernel/rcu/srcu.c

   :export:



.. kernel-doc:: kernel/rcu/tree.c

   :export:



.. kernel-doc:: kernel/rcu/tree_plugin.h

   :export:



.. kernel-doc:: kernel/rcu/update.c

   :export:



Device Resource Management

--------------------------



.. kernel-doc:: drivers/base/devres.c

   :export:

Documentation/driver-api/frame-buffer.rst

0 → 100644
+62 −0
Original line number Diff line number Diff line 
Frame Buffer Library

====================



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.



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.



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.



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.



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.



Frame Buffer Memory

-------------------



.. kernel-doc:: drivers/video/fbdev/core/fbmem.c

   :export:



Frame Buffer Colormap

---------------------



.. kernel-doc:: drivers/video/fbdev/core/fbcmap.c

   :export:



Frame Buffer Video Mode Database

--------------------------------



.. kernel-doc:: drivers/video/fbdev/core/modedb.c

   :internal:



.. kernel-doc:: drivers/video/fbdev/core/modedb.c

   :export:



Frame Buffer Macintosh Video Mode Database

------------------------------------------



.. kernel-doc:: drivers/video/fbdev/macmodes.c

   :export:



Frame Buffer Fonts

------------------



Refer to the file lib/fonts/fonts.c for more information.

Documentation/hsi.txt→Documentation/driver-api/hsi.rst

+88 −0
Original line number Diff line number Diff line 
HSI - High-speed Synchronous Serial Interface

High Speed Synchronous Serial Interface (HSI)

=============================================



1. Introduction

~~~~~~~~~~~~~~~

Introduction

---------------



High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol,

that is optimized for die-level interconnect between an Application Processor
@@ -17,6 +18,8 @@ signal can be used to wakeup the chips from standby modes. The signals are 
commonly prefixed by AC for signals going from the application die to the

cellular die and CA for signals going the other way around.



::



    +------------+                                 +---------------+

    |  Cellular  |                                 |  Application  |

    |    Die     |                                 |      Die      |
@@ -34,8 +37,8 @@ cellular die and CA for signals going the other way around. 
    |            |                                 |               |

    +------------+                                 +---------------+



2. HSI Subsystem in Linux

~~~~~~~~~~~~~~~~~~~~~~~~~

HSI Subsystem in Linux

-------------------------



In the Linux kernel the hsi subsystem is supposed to be used for HSI devices.

The hsi subsystem contains drivers for hsi controllers including support for
@@ -45,31 +48,41 @@ It also contains HSI client drivers, which make use of the generic API to 
implement a protocol used on the HSI interface. These client drivers can

use an arbitrary number of channels.



3. hsi-char Device

~~~~~~~~~~~~~~~~~~

hsi-char Device

------------------



Each port automatically registers a generic client driver called hsi_char,

which provides a charecter device for userspace representing the HSI port.

It can be used to communicate via HSI from userspace. Userspace may

configure the hsi_char device using the following ioctl commands:



* HSC_RESET:

 - flush the HSI port

HSC_RESET

 flush the HSI port



HSC_SET_PM

 enable or disable the client.



HSC_SEND_BREAK

 send break



HSC_SET_RX

 set RX configuration



HSC_GET_RX

 get RX configuration



* HSC_SET_PM

 - enable or disable the client.

HSC_SET_TX

 set TX configuration



* HSC_SEND_BREAK

 - send break

HSC_GET_TX

 get TX configuration



* HSC_SET_RX

 - set RX configuration

The kernel HSI API

------------------



* HSC_GET_RX

 - get RX configuration

.. kernel-doc:: include/linux/hsi/hsi.h

   :internal:



* HSC_SET_TX

 - set TX configuration

.. kernel-doc:: drivers/hsi/hsi_core.c

   :export:

* HSC_GET_TX

 - get TX configuration

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