[mirror_ubuntu-bionic-kernel.git] / Documentation / i2c / i2c-stub

MODULE: i2c-stub

DESCRIPTION:

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

SMBus block command support is disabled by default, and must be enabled
explicitly by setting the respective bits (0x03000000) in the functionality
module parameter.

SMBus block commands must be written to configure an SMBus command for
SMBus block operations. Writes can be partial. Block read commands always
return the number of bytes selected with the largest write so far.

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.

u8 bank_reg[10]
u8 bank_mask[10]
u8 bank_start[10]
u8 bank_end[10]:
	Optional bank settings. They tell which bits in which register
	select the active bank, as well as the range of banked registers.

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 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
6f16b75a	5	This module is a very simple fake I2C/SMBus driver. It implements six
47103178	6	types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w)
6f16b75a	7	word data, (r/w) I2C block data, and (r/w) SMBus 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
6f16b75a GR	22	SMBus block command support is disabled by default, and must be enabled
	23	explicitly by setting the respective bits (0x03000000) in the functionality
	24	module parameter.
	25
	26	SMBus block commands must be written to configure an SMBus command for
	27	SMBus block operations. Writes can be partial. Block read commands always
	28	return the number of bytes selected with the largest write so far.
	29
1da177e4 LT	30	The typical use-case is like this:
1da177e4 LT	31	1. load this module
6471b689 JD	32	2. use i2cset (from the i2c-tools project) to pre-load some data
6471b689 JD	33	3. load the target chip driver module
1da177e4 LT	34	4. observe its behavior in the kernel log
1da177e4 LT	35
b3af547e JD	36	There's a script named i2c-stub-from-dump in the i2c-tools package which
	37	can load register values automatically from a chip dump.
	38
7a8d29ce JD	39	PARAMETERS:
7a8d29ce JD	40
9d90c1fd JD	41	int chip_addr[10]:
9d90c1fd JD	42	The SMBus addresses to emulate chips at.
7a8d29ce	43
38f41f28 JD	44	unsigned long functionality:
	45	Functionality override, to disable some commands. See I2C_FUNC_*
	46	constants in <linux/i2c.h> for the suitable values. For example,
	47	value 0x1f0000 would only enable the quick, byte and byte data
	48	commands.
	49
2408c17f JD	50	u8 bank_reg[10]
	51	u8 bank_mask[10]
	52	u8 bank_start[10]
	53	u8 bank_end[10]:
	54	Optional bank settings. They tell which bits in which register
	55	select the active bank, as well as the range of banked registers.
	56
1da177e4 LT	57	CAVEATS:
1da177e4 LT	58
1da177e4 LT	59	If your target driver polls some byte or word waiting for it to change, the
	60	stub could lock it up. Use i2cset to unlock it.
	61
1da177e4 LT	62	If you spam it hard enough, printk can be lossy. This module really wants
	63	something like relayfs.
	64