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linux/Documentation/i2c/summary.rst

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docs: i2c: rename sections so the overall picture is clearer Some of the section names are not very clear. Reading those names in the index.rst page does not help much in grasping what the content is supposed to be. Rename those sections to clarify their content, especially when reading the index page. Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net> Acked-by: Peter Rosin <peda@axentia.se> Reviewed-by: Jean Delvare <jdelvare@suse.de> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2020-01-29 18:19:51 +03:00
=============================
Introduction to I2C and SMBus
=============================
Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 02:20:36 +04:00
docs: i2c: summary: extend introduction - state the "official" name (I²C, not I2C, according to the spec) at the beginning but keep using the more practical I2C elsewhere - mention some known different names - add link to the specification document Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net> Reviewed-by: Jean Delvare <jdelvare@suse.de> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2020-01-29 18:19:27 +03:00
I²C (pronounce: I squared C and written I2C in the kernel documentation) is
a protocol developed by Philips. It is a slow two-wire protocol (variable
speed, up to 400 kHz), with a high speed extension (3.4 MHz). It provides
an inexpensive bus for connecting many types of devices with infrequent or
low bandwidth communications needs. I2C is widely used with embedded
systems. Some systems use variants that don't meet branding requirements,
and so are not advertised as being I2C but come under different names,
e.g. TWI (Two Wire Interface), IIC.
The official I2C specification is the `"I2C-bus specification and user
manual" (UM10204) <https://www.nxp.com/docs/en/user-guide/UM10204.pdf>`_
published by NXP Semiconductors.
Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 02:20:36 +04:00
i2c: i2c probe() and remove() documented Update Documentation/i2c to match previous patches updating probe() and remove() logic. Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Signed-off-by: Jean Delvare <khali@linux-fr.org>
2007-05-02 01:26:31 +04:00
SMBus (System Management Bus) is based on the I2C protocol, and is mostly
a subset of I2C protocols and signaling. Many I2C devices will work on an
SMBus, but some SMBus protocols add semantics beyond what is required to
achieve I2C branding. Modern PC mainboards rely on SMBus. The most common
devices connected through SMBus are RAM modules configured using I2C EEPROMs,
and hardware monitoring chips.
Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 02:20:36 +04:00
i2c: i2c probe() and remove() documented Update Documentation/i2c to match previous patches updating probe() and remove() logic. Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Signed-off-by: Jean Delvare <khali@linux-fr.org>
2007-05-02 01:26:31 +04:00
Because the SMBus is mostly a subset of the generalized I2C bus, we can
use its protocols on many I2C systems. However, there are systems that don't
meet both SMBus and I2C electrical constraints; and others which can't
implement all the common SMBus protocol semantics or messages.
Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 02:20:36 +04:00
Terminology
===========
docs: i2c: summary: rewrite the "terminology" section This section, partly dating back to the pre-git era, is somewhat unclear and partly incorrect. Rewrite it almost completely including a reference figure, concise but precise definition of each term and the paths where drivers are found. Particular care has been put in clarifying the relation between adapter and algorithm, which has no correspondence in the I2C spec terminology. Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net> Reviewed-by: Jean Delvare <jdelvare@suse.de> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2020-01-29 18:19:28 +03:00
Using the terminology from the official documentation, the I2C bus connects
one or more *master* chips and one or more *slave* chips.
docs: i2c: convert to ReST and add to driver-api bookset Convert each file at I2C subsystem, renaming them to .rst and adding to the driver-api book. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Wolfram Sang <wsa@the-dreams.de> Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com> Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-07-26 15:51:16 +03:00
docs: i2c: summary: rewrite the "terminology" section This section, partly dating back to the pre-git era, is somewhat unclear and partly incorrect. Rewrite it almost completely including a reference figure, concise but precise definition of each term and the paths where drivers are found. Particular care has been put in clarifying the relation between adapter and algorithm, which has no correspondence in the I2C spec terminology. Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net> Reviewed-by: Jean Delvare <jdelvare@suse.de> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2020-01-29 18:19:28 +03:00
.. kernel-figure:: i2c.svg
:alt: Simple I2C bus with one master and 3 slaves
Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 02:20:36 +04:00
docs: i2c: summary: rewrite the "terminology" section This section, partly dating back to the pre-git era, is somewhat unclear and partly incorrect. Rewrite it almost completely including a reference figure, concise but precise definition of each term and the paths where drivers are found. Particular care has been put in clarifying the relation between adapter and algorithm, which has no correspondence in the I2C spec terminology. Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net> Reviewed-by: Jean Delvare <jdelvare@suse.de> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2020-01-29 18:19:28 +03:00
Simple I2C bus
i2c: i2c probe() and remove() documented Update Documentation/i2c to match previous patches updating probe() and remove() logic. Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Signed-off-by: Jean Delvare <khali@linux-fr.org>
2007-05-02 01:26:31 +04:00
docs: i2c: summary: rewrite the "terminology" section This section, partly dating back to the pre-git era, is somewhat unclear and partly incorrect. Rewrite it almost completely including a reference figure, concise but precise definition of each term and the paths where drivers are found. Particular care has been put in clarifying the relation between adapter and algorithm, which has no correspondence in the I2C spec terminology. Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net> Reviewed-by: Jean Delvare <jdelvare@suse.de> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2020-01-29 18:19:28 +03:00
A **master** chip is a node that starts communications with slaves. In the
Linux kernel implementation it is called an **adapter** or bus. Adapter
drivers are in the ``drivers/i2c/busses/`` subdirectory.
Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 02:20:36 +04:00
docs: i2c: summary: rewrite the "terminology" section This section, partly dating back to the pre-git era, is somewhat unclear and partly incorrect. Rewrite it almost completely including a reference figure, concise but precise definition of each term and the paths where drivers are found. Particular care has been put in clarifying the relation between adapter and algorithm, which has no correspondence in the I2C spec terminology. Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net> Reviewed-by: Jean Delvare <jdelvare@suse.de> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2020-01-29 18:19:28 +03:00
An **algorithm** contains general code that can be used to implement a
whole class of I2C adapters. Each specific adapter driver either depends on
an algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes
its own implementation.
A **slave** chip is a node that responds to communications when addressed
by the master. In Linux it is called a **client**. Client drivers are kept
in a directory specific to the feature they provide, for example
``drivers/media/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for
video-related chips.
For the example configuration in figure, you will need a driver for your
I2C adapter, and drivers for your I2C devices (usually one driver for each
device).
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