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docs: i2c: summary: be clearer with 'controller/target' and 'adapter/client' pairs

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This not only includes rewording, but also where to put which emphasis
on terms in this document.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
This commit is contained in:
Wolfram Sang 2024-06-21 09:30:13 +02:00
parent 1e926ea190
commit 20738cb9fa
1 changed files with 24 additions and 17 deletions
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Documentation/i2c/summary.rst
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@ -31,9 +31,7 @@ implement all the common SMBus protocol semantics or messages.
Terminology
===========
The I2C bus connects one or more *controller* chips and one or more *target*
chips.
The I2C bus connects one or more controller chips and one or more target chips.
.. kernel-figure:: i2c_bus.svg
:alt: Simple I2C bus with one controller and 3 targets
@ -41,28 +39,37 @@ chips.
Simple I2C bus
A **controller** chip is a node that starts communications with targets. In the
Linux kernel implementation it is called an **adapter** or bus. Adapter
drivers are in the ``drivers/i2c/busses/`` subdirectory.
Linux kernel implementation it is also called an "adapter" or "bus". Controller
drivers are usually in the ``drivers/i2c/busses/`` subdirectory.
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.
An **algorithm** contains general code that can be used to implement a whole
class of I2C controllers. Each specific controller driver either depends on an
algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes its
own implementation.
A **target** chip is a node that responds to communications when addressed by a
controller. In the Linux kernel implementation it is called a **client**. While
targets are usually separate external chips, Linux can also act as a target
(needs hardware support) and respond to another controller on the bus. This is
then called a **local target**. In contrast, an external chip is called a
**remote target**.
controller. In the Linux kernel implementation it is also called a "client".
While targets are usually separate external chips, Linux can also act as a
target (needs hardware support) and respond to another controller on the bus.
This is then called a **local target**. In contrast, an external chip is called
a **remote target**.
Target drivers are kept in a directory specific to the feature they provide,
for example ``drivers/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).
For the example configuration in the figure above, you will need one driver for
the I2C controller, and drivers for your I2C targets. Usually one driver for
each target.
Synonyms
--------
As mentioned above, the Linux I2C implementation historically uses the terms
"adapter" for controller and "client" for target. A number of data structures
have these synonyms in their name. So, when discussing implementation details,
you should be aware of these terms as well. The official wording is preferred,
though.
Outdated terminology
--------------------