linux-pinenote/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 a chip address as a module parameter when loading
this driver, which will then only react to SMBus commands to this address.

No hardware is needed nor associated with this module.  It will accept write
quick commands to one address; it will respond to the other commands (also
to one address) by reading from or writing to an array 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:
	The SMBus address to emulate a chip 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.

Only one chip address is supported - although this module could be
extended to support more.

If you spam it hard enough, printk can be lossy.  This module really wants
something like relayfs.