| Kyle Swenson | 8d8f654 | 2021-03-15 11:02:55 -0600 | [diff] [blame^] | 1 | MODULE: i2c-stub |
| 2 | |
| 3 | DESCRIPTION: |
| 4 | |
| 5 | This module is a very simple fake I2C/SMBus driver. It implements six |
| 6 | types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w) |
| 7 | word data, (r/w) I2C block data, and (r/w) SMBus block data. |
| 8 | |
| 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. |
| 11 | |
| 12 | No hardware is needed nor associated with this module. It will accept write |
| 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. |
| 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 | |
| 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 | |
| 30 | The typical use-case is like this: |
| 31 | 1. load this module |
| 32 | 2. use i2cset (from the i2c-tools project) to pre-load some data |
| 33 | 3. load the target chip driver module |
| 34 | 4. observe its behavior in the kernel log |
| 35 | |
| 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 | |
| 39 | PARAMETERS: |
| 40 | |
| 41 | int chip_addr[10]: |
| 42 | The SMBus addresses to emulate chips at. |
| 43 | |
| 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 | |
| 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 | |
| 57 | CAVEATS: |
| 58 | |
| 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 | |
| 62 | If you spam it hard enough, printk can be lossy. This module really wants |
| 63 | something like relayfs. |
| 64 | |