Commit | Line | Data |
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ccf988b6 MCC |
1 | ======== |
2 | i2c-stub | |
3 | ======== | |
1da177e4 | 4 | |
ccf988b6 MCC |
5 | Description |
6 | =========== | |
1da177e4 | 7 | |
6f16b75a | 8 | This module is a very simple fake I2C/SMBus driver. It implements six |
47103178 | 9 | types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w) |
6f16b75a | 10 | word data, (r/w) I2C block data, and (r/w) SMBus block data. |
1da177e4 | 11 | |
9d90c1fd JD |
12 | You need to provide chip addresses as a module parameter when loading this |
13 | driver, which will then only react to SMBus commands to these addresses. | |
7a8d29ce | 14 | |
1da177e4 | 15 | No hardware is needed nor associated with this module. It will accept write |
9d90c1fd JD |
16 | quick commands to the specified addresses; it will respond to the other |
17 | commands (also to the specified addresses) by reading from or writing to | |
18 | arrays in memory. It will also spam the kernel logs for every command it | |
19 | handles. | |
1da177e4 LT |
20 | |
21 | A pointer register with auto-increment is implemented for all byte | |
22 | operations. This allows for continuous byte reads like those supported by | |
23 | EEPROMs, among others. | |
24 | ||
6f16b75a GR |
25 | SMBus block command support is disabled by default, and must be enabled |
26 | explicitly by setting the respective bits (0x03000000) in the functionality | |
27 | module parameter. | |
28 | ||
29 | SMBus block commands must be written to configure an SMBus command for | |
30 | SMBus block operations. Writes can be partial. Block read commands always | |
31 | return the number of bytes selected with the largest write so far. | |
32 | ||
1da177e4 | 33 | The typical use-case is like this: |
ccf988b6 | 34 | |
1da177e4 | 35 | 1. load this module |
6471b689 JD |
36 | 2. use i2cset (from the i2c-tools project) to pre-load some data |
37 | 3. load the target chip driver module | |
1da177e4 LT |
38 | 4. observe its behavior in the kernel log |
39 | ||
b3af547e JD |
40 | There's a script named i2c-stub-from-dump in the i2c-tools package which |
41 | can load register values automatically from a chip dump. | |
42 | ||
ccf988b6 MCC |
43 | Parameters |
44 | ========== | |
7a8d29ce | 45 | |
9d90c1fd JD |
46 | int chip_addr[10]: |
47 | The SMBus addresses to emulate chips at. | |
7a8d29ce | 48 | |
38f41f28 JD |
49 | unsigned 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 | ||
ccf988b6 | 55 | u8 bank_reg[10], u8 bank_mask[10], u8 bank_start[10], u8 bank_end[10]: |
2408c17f JD |
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 | ||
ccf988b6 MCC |
59 | Caveats |
60 | ======= | |
1da177e4 | 61 | |
1da177e4 LT |
62 | If your target driver polls some byte or word waiting for it to change, the |
63 | stub could lock it up. Use i2cset to unlock it. | |
64 | ||
1da177e4 LT |
65 | If you spam it hard enough, printk can be lossy. This module really wants |
66 | something like relayfs. |