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i2c: Add kernel documentation

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Generate I2C kerneldoc; fix various glitches and add "context" sections to
that documentation.  Most I2C and SMBus functions still have no kerneldoc.

Let me suggest providing kerneldoc for all the i2c_smbus_*() functions as
a small and mostly self-contained project for anyone so inclined.  :)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
This commit is contained in:
David Brownell 2007-07-12 14:12:28 +02:00 • committed by Jean Delvare
parent 4eb6bf6bfb
commit d64f73be1b
3 changed files with 76 additions and 3 deletions
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55
Documentation/DocBook/kernel-api.tmpl
View file

@ -643,6 +643,60 @@ X!Idrivers/video/console/fonts.c
!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="splice">
<title>splice API</title>
<para>)
@ -654,4 +708,5 @@ X!Idrivers/video/console/fonts.c
!Ffs/splice.c
</chapter>
</book>