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diff --git a/Documentation/i2c/summary.rst b/Documentation/i2c/summary.rst index 3a24eac17375..ce7230025b33 100644 --- a/Documentation/i2c/summary.rst +++ b/Documentation/i2c/summary.rst @@ -1,13 +1,19 @@ -============= -I2C and SMBus -============= - -I2C (pronounce: I squared C) 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. +============================= +Introduction to I2C and SMBus +============================= + +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. 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 @@ -25,21 +31,29 @@ implement all the common SMBus protocol semantics or messages. Terminology =========== -When we talk about I2C, we use the following terms:: +Using the terminology from the official documentation, the I2C bus connects +one or more *master* chips and one or more *slave* chips. + +.. kernel-figure:: i2c.svg + :alt: Simple I2C bus with one master and 3 slaves + + Simple I2C bus - Bus -> Algorithm - Adapter - Device -> Driver - Client +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. -An Algorithm driver contains general code that can be used for a whole class -of I2C adapters. Each specific adapter driver either depends on one algorithm -driver, or includes its own implementation. +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 Driver driver (yes, this sounds ridiculous, sorry) contains the general -code to access some type of device. Each detected device gets its own -data in the Client structure. Usually, Driver and Client are more closely -integrated than Algorithm and Adapter. +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 a given configuration, you will need a driver for your I2C bus, and -drivers for your I2C devices (usually one driver for each device). +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). |