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1da177e4 LT |
1 | MODULE: i2c-stub |
2 | ||
3 | DESCRIPTION: | |
4 | ||
6f16b75a | 5 | This module is a very simple fake I2C/SMBus driver. It implements six |
47103178 | 6 | types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w) |
6f16b75a | 7 | word data, (r/w) I2C block data, and (r/w) SMBus block data. |
1da177e4 | 8 | |
9d90c1fd JD |
9 | You need to provide chip addresses as a module parameter when loading this |
10 | driver, which will then only react to SMBus commands to these addresses. | |
7a8d29ce | 11 | |
1da177e4 | 12 | No hardware is needed nor associated with this module. It will accept write |
9d90c1fd JD |
13 | quick commands to the specified addresses; it will respond to the other |
14 | commands (also to the specified addresses) by reading from or writing to | |
15 | arrays in memory. It will also spam the kernel logs for every command it | |
16 | handles. | |
1da177e4 LT |
17 | |
18 | A pointer register with auto-increment is implemented for all byte | |
19 | operations. This allows for continuous byte reads like those supported by | |
20 | EEPROMs, among others. | |
21 | ||
6f16b75a GR |
22 | SMBus block command support is disabled by default, and must be enabled |
23 | explicitly by setting the respective bits (0x03000000) in the functionality | |
24 | module parameter. | |
25 | ||
26 | SMBus block commands must be written to configure an SMBus command for | |
27 | SMBus block operations. Writes can be partial. Block read commands always | |
28 | return the number of bytes selected with the largest write so far. | |
29 | ||
1da177e4 LT |
30 | The typical use-case is like this: |
31 | 1. load this module | |
6471b689 JD |
32 | 2. use i2cset (from the i2c-tools project) to pre-load some data |
33 | 3. load the target chip driver module | |
1da177e4 LT |
34 | 4. observe its behavior in the kernel log |
35 | ||
b3af547e JD |
36 | There's a script named i2c-stub-from-dump in the i2c-tools package which |
37 | can load register values automatically from a chip dump. | |
38 | ||
7a8d29ce JD |
39 | PARAMETERS: |
40 | ||
9d90c1fd JD |
41 | int chip_addr[10]: |
42 | The SMBus addresses to emulate chips at. | |
7a8d29ce | 43 | |
38f41f28 JD |
44 | unsigned long functionality: |
45 | Functionality override, to disable some commands. See I2C_FUNC_* | |
46 | constants in <linux/i2c.h> for the suitable values. For example, | |
47 | value 0x1f0000 would only enable the quick, byte and byte data | |
48 | commands. | |
49 | ||
2408c17f JD |
50 | u8 bank_reg[10] |
51 | u8 bank_mask[10] | |
52 | u8 bank_start[10] | |
53 | u8 bank_end[10]: | |
54 | Optional bank settings. They tell which bits in which register | |
55 | select the active bank, as well as the range of banked registers. | |
56 | ||
1da177e4 LT |
57 | CAVEATS: |
58 | ||
1da177e4 LT |
59 | If your target driver polls some byte or word waiting for it to change, the |
60 | stub could lock it up. Use i2cset to unlock it. | |
61 | ||
1da177e4 LT |
62 | If you spam it hard enough, printk can be lossy. This module really wants |
63 | something like relayfs. | |
64 |