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Diffstat (limited to 'Documentation/i2c/i2c-stub')
| -rw-r--r-- | Documentation/i2c/i2c-stub | 40 |
1 files changed, 22 insertions, 18 deletions
diff --git a/Documentation/i2c/i2c-stub b/Documentation/i2c/i2c-stub index 9cc081e6976..fa4b669c166 100644 --- a/Documentation/i2c/i2c-stub +++ b/Documentation/i2c/i2c-stub @@ -2,17 +2,18 @@ MODULE: i2c-stub DESCRIPTION: -This module is a very simple fake I2C/SMBus driver. It implements four -types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, and -(r/w) word data. +This module is a very simple fake I2C/SMBus driver. It implements five +types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w) +word data, and (r/w) I2C block data. -You need to provide a chip address as a module parameter when loading -this driver, which will then only react to SMBus commands to this address. +You need to provide chip addresses as a module parameter when loading this +driver, which will then only react to SMBus commands to these addresses. No hardware is needed nor associated with this module. It will accept write -quick commands to one address; it will respond to the other commands (also -to one address) by reading from or writing to an array in memory. It will -also spam the kernel logs for every command it handles. +quick commands to the specified addresses; it will respond to the other +commands (also to the specified addresses) by reading from or writing to +arrays in memory. It will also spam the kernel logs for every command it +handles. A pointer register with auto-increment is implemented for all byte operations. This allows for continuous byte reads like those supported by @@ -20,19 +21,25 @@ EEPROMs, among others. The typical use-case is like this: 1. load this module - 2. use i2cset (from lm_sensors project) to pre-load some data - 3. load the target sensors chip driver module + 2. use i2cset (from the i2c-tools project) to pre-load some data + 3. load the target chip driver module 4. observe its behavior in the kernel log +There's a script named i2c-stub-from-dump in the i2c-tools package which +can load register values automatically from a chip dump. + PARAMETERS: -int chip_addr: - The SMBus address to emulate a chip at. +int chip_addr[10]: + The SMBus addresses to emulate chips at. -CAVEATS: +unsigned long functionality: + Functionality override, to disable some commands. See I2C_FUNC_* + constants in <linux/i2c.h> for the suitable values. For example, + value 0x1f0000 would only enable the quick, byte and byte data + commands. -There are independent arrays for byte/data and word/data commands. Depending -on if/how a target driver mixes them, you'll need to be careful. +CAVEATS: If your target driver polls some byte or word waiting for it to change, the stub could lock it up. Use i2cset to unlock it. @@ -41,9 +48,6 @@ If the hardware for your driver has banked registers (e.g. Winbond sensors chips) this module will not work well - although it could be extended to support that pretty easily. -Only one chip address is supported - although this module could be -extended to support more. - If you spam it hard enough, printk can be lossy. This module really wants something like relayfs. |