From 849369d6c66d3054688672f97d31fceb8e8230fb Mon Sep 17 00:00:00 2001 From: root Date: Fri, 25 Dec 2015 04:40:36 +0000 Subject: initial_commit --- Documentation/i2c/i2c-stub | 53 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100644 Documentation/i2c/i2c-stub (limited to 'Documentation/i2c/i2c-stub') diff --git a/Documentation/i2c/i2c-stub b/Documentation/i2c/i2c-stub new file mode 100644 index 00000000..fa4b669c --- /dev/null +++ b/Documentation/i2c/i2c-stub @@ -0,0 +1,53 @@ +MODULE: i2c-stub + +DESCRIPTION: + +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 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 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 +EEPROMs, among others. + +The typical use-case is like this: + 1. load this 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[10]: + The SMBus addresses to emulate chips at. + +unsigned long functionality: + Functionality override, to disable some commands. See I2C_FUNC_* + constants in for the suitable values. For example, + value 0x1f0000 would only enable the quick, byte and byte data + commands. + +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. + +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. + +If you spam it hard enough, printk can be lossy. This module really wants +something like relayfs. + -- cgit v1.2.3