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

MODULE: i2c-stub

DESCRIPTION:

This module is a very simple fake I2C/SMBus driver.  It implements five
types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w)
word data, and (r/w) I2C block 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 the i2c-tools project) to pre-load some data
	3. load the target chip driver module
	4. observe its behavior in the kernel log

There's a script named i2c-stub-from-dump in the i2c-tools package which
can load register values automatically from a chip dump.

PARAMETERS:

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

unsigned long functionality:
	Functionality override, to disable some commands. See I2C_FUNC_*
	constants in <linux/i2c.h> for the suitable values. For example,
	value 0x1f0000 would only enable the quick, byte and byte data
	commands.

CAVEATS:

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
47103178 JD	5	This module is a very simple fake I2C/SMBus driver. It implements five
	6	types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w)
	7	word data, and (r/w) I2C block data.
1da177e4	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
6471b689 JD	24	2. use i2cset (from the i2c-tools project) to pre-load some data
6471b689 JD	25	3. load the target chip driver module
1da177e4 LT	26	4. observe its behavior in the kernel log
1da177e4 LT	27
b3af547e JD	28	There's a script named i2c-stub-from-dump in the i2c-tools package which
	29	can load register values automatically from a chip dump.
	30
7a8d29ce JD	31	PARAMETERS:
7a8d29ce JD	32
9d90c1fd JD	33	int chip_addr[10]:
9d90c1fd JD	34	The SMBus addresses to emulate chips at.
7a8d29ce	35
38f41f28 JD	36	unsigned long functionality:
	37	Functionality override, to disable some commands. See I2C_FUNC_*
	38	constants in <linux/i2c.h> for the suitable values. For example,
	39	value 0x1f0000 would only enable the quick, byte and byte data
	40	commands.
	41
1da177e4 LT	42	CAVEATS:
1da177e4 LT	43
1da177e4 LT	44	If your target driver polls some byte or word waiting for it to change, the
	45	stub could lock it up. Use i2cset to unlock it.
	46
	47	If the hardware for your driver has banked registers (e.g. Winbond sensors
	48	chips) this module will not work well - although it could be extended to
	49	support that pretty easily.
	50
	51	If you spam it hard enough, printk can be lossy. This module really wants
	52	something like relayfs.
	53