[linux-block.git] / Documentation / i2c / i2c-stub

MODULE: i2c-stub

DESCRIPTION:

This module is a very simple fake I2C/SMBus driver.  It implements four
types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, and
(r/w) word data.

You need to provide chip addresses as a module parameter when loading this
driver, which will then only react to SMBus commands to these addresses.

No hardware is needed nor associated with this module.  It will accept write
quick commands to the specified addresses; it will respond to the other
commands (also to the specified addresses) by reading from or writing to
arrays in memory.  It will also spam the kernel logs for every command it
handles.

A pointer register with auto-increment is implemented for all byte
operations.  This allows for continuous byte reads like those supported by
EEPROMs, among others.

The typical use-case is like this:
	1. load this module
	2. use i2cset (from lm_sensors project) to pre-load some data
	3. load the target sensors chip driver module
	4. observe its behavior in the kernel log

PARAMETERS:

int chip_addr[10]:
	The SMBus addresses to emulate chips at.

CAVEATS:

There are independent arrays for byte/data and word/data commands.  Depending
on if/how a target driver mixes them, you'll need to be careful.

If your target driver polls some byte or word waiting for it to change, the
stub could lock it up.  Use i2cset to unlock it.

If the hardware for your driver has banked registers (e.g. Winbond sensors
chips) this module will not work well - although it could be extended to
support that pretty easily.

If you spam it hard enough, printk can be lossy.  This module really wants
something like relayfs.
Commit	Line	Data
1da177e4 LT	1	MODULE: i2c-stub
	2
	3	DESCRIPTION:
	4
	5	This module is a very simple fake I2C/SMBus driver. It implements four
	6	types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, and
	7	(r/w) word data.
	8
9d90c1fd JD	9	You need to provide chip addresses as a module parameter when loading this
9d90c1fd JD	10	driver, which will then only react to SMBus commands to these addresses.
7a8d29ce	11
1da177e4	12	No hardware is needed nor associated with this module. It will accept write
9d90c1fd JD	13	quick commands to the specified addresses; it will respond to the other
	14	commands (also to the specified addresses) by reading from or writing to
	15	arrays in memory. It will also spam the kernel logs for every command it
	16	handles.
1da177e4 LT	17
	18	A pointer register with auto-increment is implemented for all byte
	19	operations. This allows for continuous byte reads like those supported by
	20	EEPROMs, among others.
	21
	22	The typical use-case is like this:
	23	1. load this module
	24	2. use i2cset (from lm_sensors project) to pre-load some data
	25	3. load the target sensors chip driver module
	26	4. observe its behavior in the kernel log
	27
7a8d29ce JD	28	PARAMETERS:
7a8d29ce JD	29
9d90c1fd JD	30	int chip_addr[10]:
9d90c1fd JD	31	The SMBus addresses to emulate chips at.
7a8d29ce	32
1da177e4 LT	33	CAVEATS:
	34
	35	There are independent arrays for byte/data and word/data commands. Depending
	36	on if/how a target driver mixes them, you'll need to be careful.
	37
	38	If your target driver polls some byte or word waiting for it to change, the
	39	stub could lock it up. Use i2cset to unlock it.
	40
	41	If the hardware for your driver has banked registers (e.g. Winbond sensors
	42	chips) this module will not work well - although it could be extended to
	43	support that pretty easily.
	44
	45	If you spam it hard enough, printk can be lossy. This module really wants
	46	something like relayfs.
	47