1========
2i2c-stub
3========
4
5Description
6===========
7
8This module is a very simple fake I2C/SMBus driver.  It implements six
9types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w)
10word data, (r/w) I2C block data, and (r/w) SMBus block data.
11
12You need to provide chip addresses as a module parameter when loading this
13driver, which will then only react to SMBus commands to these addresses.
14
15No hardware is needed nor associated with this module.  It will accept write
16quick commands to the specified addresses; it will respond to the other
17commands (also to the specified addresses) by reading from or writing to
18arrays in memory.  It will also spam the kernel logs for every command it
19handles.
20
21A pointer register with auto-increment is implemented for all byte
22operations.  This allows for continuous byte reads like those supported by
23EEPROMs, among others.
24
25SMBus block command support is disabled by default, and must be enabled
26explicitly by setting the respective bits (0x03000000) in the functionality
27module parameter.
28
29SMBus block commands must be written to configure an SMBus command for
30SMBus block operations. Writes can be partial. Block read commands always
31return the number of bytes selected with the largest write so far.
32
33The typical use-case is like this:
34
35	1. load this module
36	2. use i2cset (from the i2c-tools project) to pre-load some data
37	3. load the target chip driver module
38	4. observe its behavior in the kernel log
39
40There's a script named i2c-stub-from-dump in the i2c-tools package which
41can load register values automatically from a chip dump.
42
43Parameters
44==========
45
46int chip_addr[10]:
47	The SMBus addresses to emulate chips at.
48
49unsigned long functionality:
50	Functionality override, to disable some commands. See I2C_FUNC_*
51	constants in <linux/i2c.h> for the suitable values. For example,
52	value 0x1f0000 would only enable the quick, byte and byte data
53	commands.
54
55u8 bank_reg[10], u8 bank_mask[10], u8 bank_start[10], u8 bank_end[10]:
56	Optional bank settings. They tell which bits in which register
57	select the active bank, as well as the range of banked registers.
58
59Caveats
60=======
61
62If your target driver polls some byte or word waiting for it to change, the
63stub could lock it up.  Use i2cset to unlock it.
64
65If you spam it hard enough, printk can be lossy.  This module really wants
66something like relayfs.
67