i2c-stub

Description

This module is a very simple fake I2C/SMBus driver. It implements sixtypes 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 thisdriver, which will then only react to SMBus commands to these addresses.

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

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

SMBus block command support is disabled by default, and must be enabledexplicitly by setting the respective bits (0x03000000) in the functionalitymodule parameter.

SMBus block commands must be written to configure an SMBus command forSMBus block operations. Writes can be partial. Block read commands alwaysreturn 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 whichcan 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 datacommands.
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 registerselect 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, thestub could lock it up. Use i2cset to unlock it.

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