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1da177e4 LT |
1 | MODULE: i2c-stub |
2 | ||
3 | DESCRIPTION: | |
4 | ||
5 | This module is a very simple fake I2C/SMBus driver. It implements four | |
6 | types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, and | |
7 | (r/w) word data. | |
8 | ||
7a8d29ce JD |
9 | You need to provide a chip address as a module parameter when loading |
10 | this driver, which will then only react to SMBus commands to this address. | |
11 | ||
1da177e4 | 12 | No hardware is needed nor associated with this module. It will accept write |
7a8d29ce JD |
13 | quick commands to one address; it will respond to the other commands (also |
14 | to one address) by reading from or writing to an array in memory. It will | |
1da177e4 LT |
15 | also spam the kernel logs for every command it handles. |
16 | ||
17 | A pointer register with auto-increment is implemented for all byte | |
18 | operations. This allows for continuous byte reads like those supported by | |
19 | EEPROMs, among others. | |
20 | ||
21 | The typical use-case is like this: | |
22 | 1. load this module | |
23 | 2. use i2cset (from lm_sensors project) to pre-load some data | |
24 | 3. load the target sensors chip driver module | |
25 | 4. observe its behavior in the kernel log | |
26 | ||
7a8d29ce JD |
27 | PARAMETERS: |
28 | ||
29 | int chip_addr: | |
30 | The SMBus address to emulate a chip at. | |
31 | ||
1da177e4 LT |
32 | CAVEATS: |
33 | ||
34 | There are independent arrays for byte/data and word/data commands. Depending | |
35 | on if/how a target driver mixes them, you'll need to be careful. | |
36 | ||
37 | If your target driver polls some byte or word waiting for it to change, the | |
38 | stub could lock it up. Use i2cset to unlock it. | |
39 | ||
40 | If the hardware for your driver has banked registers (e.g. Winbond sensors | |
41 | chips) this module will not work well - although it could be extended to | |
42 | support that pretty easily. | |
43 | ||
7a8d29ce JD |
44 | Only one chip address is supported - although this module could be |
45 | extended to support more. | |
46 | ||
1da177e4 LT |
47 | If you spam it hard enough, printk can be lossy. This module really wants |
48 | something like relayfs. | |
49 |