mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-22 12:14:01 +08:00
0a85e9a271
This driver has been broken forever. It depends on i2c-algo-8xx which has never been in the mainline kernel. Signed-off-by: Jean Delvare <khali@linux-fr.org>
85 lines
3.3 KiB
Plaintext
85 lines
3.3 KiB
Plaintext
This is an explanation of what i2c is, and what is supported in this package.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
|
|
Terminology
|
|
===========
|
|
|
|
When we talk about I2C, we use the following terms:
|
|
Bus -> Algorithm
|
|
Adapter
|
|
Device -> Driver
|
|
Client
|
|
|
|
An Algorithm driver contains general code that can be used for a whole class
|
|
of I2C adapters. Each specific adapter driver depends on one algorithm
|
|
driver.
|
|
|
|
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.
|
|
|
|
For a given configuration, you will need a driver for your I2C bus (usually
|
|
a separate Adapter and Algorithm driver), and drivers for your I2C devices
|
|
(usually one driver for each device). There are no I2C device drivers
|
|
in this package. See the lm_sensors project http://www.lm-sensors.nu
|
|
for device drivers.
|
|
|
|
At this time, Linux only operates I2C (or SMBus) in master mode; you can't
|
|
use these APIs to make a Linux system behave as a slave/device, either to
|
|
speak a custom protocol or to emulate some other device.
|
|
|
|
|
|
Included Bus Drivers
|
|
====================
|
|
Note that only stable drivers are patched into the kernel by 'mkpatch'.
|
|
|
|
|
|
Base modules
|
|
------------
|
|
|
|
i2c-core: The basic I2C code, including the /proc/bus/i2c* interface
|
|
i2c-dev: The /dev/i2c-* interface
|
|
i2c-proc: The /proc/sys/dev/sensors interface for device (client) drivers
|
|
|
|
Algorithm drivers
|
|
-----------------
|
|
|
|
i2c-algo-bit: A bit-banging algorithm
|
|
i2c-algo-pcf: A PCF 8584 style algorithm
|
|
i2c-algo-ibm_ocp: An algorithm for the I2C device in IBM 4xx processors (NOT BUILT BY DEFAULT)
|
|
|
|
Adapter drivers
|
|
---------------
|
|
|
|
i2c-elektor: Elektor ISA card (uses i2c-algo-pcf)
|
|
i2c-elv: ELV parallel port adapter (uses i2c-algo-bit)
|
|
i2c-pcf-epp: PCF8584 on a EPP parallel port (uses i2c-algo-pcf) (NOT mkpatched)
|
|
i2c-philips-par: Philips style parallel port adapter (uses i2c-algo-bit)
|
|
i2c-adap-ibm_ocp: IBM 4xx processor I2C device (uses i2c-algo-ibm_ocp) (NOT BUILT BY DEFAULT)
|
|
i2c-pport: Primitive parallel port adapter (uses i2c-algo-bit)
|
|
i2c-velleman: Velleman K8000 parallel port adapter (uses i2c-algo-bit)
|
|
|