Diffstat (limited to 'Documentation/i2c/i2c-stub')
1 files changed, 38 insertions, 0 deletions
diff --git a/Documentation/i2c/i2c-stub b/Documentation/i2c/i2c-stub
new file mode 100644
@@ -0,0 +1,38 @@
+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.
+No hardware is needed nor associated with this module. It will accept write
+quick commands to all addresses; it will respond to the other commands (also
+to all addresses) by reading from or writing to an array 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 lm_sensors project) to pre-load some data
+ 3. load the target sensors chip driver module
+ 4. observe its behavior in the kernel log
+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.
+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.