Commit 20738cb9 authored by Wolfram Sang's avatar Wolfram Sang
Browse files

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



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

Signed-off-by: default avatarWolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: default avatarEaswar Hariharan <eahariha@linux.microsoft.com>
Signed-off-by: default avatarWolfram Sang <wsa+renesas@sang-engineering.com>
parent 1e926ea1

Documentation/i2c/summary.rst

+24 −17
Original line number Diff line number Diff line
@@ -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

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