path: root/Documentation/i2c/i2c-stub
diff options
Diffstat (limited to 'Documentation/i2c/i2c-stub')
1 files changed, 53 insertions, 0 deletions
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
+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
+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.
+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 <linux/i2c.h> for the suitable values. For example,
+ value 0x1f0000 would only enable the quick, byte and byte data
+ commands.
+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.