These changes are the raw update to linux-4.4.6-rt14. Kernel sources

[kvmfornfv.git] / kernel / Documentation / i2c / slave-interface

diff --git a/kernel/Documentation/i2c/slave-interface b/kernel/Documentation/i2c/slave-interface
index b228ca5..61ed05c 100644 (file)
--- a/kernel/Documentation/i2c/slave-interface
+++ b/kernel/Documentation/i2c/slave-interface
@@ -3,16 +3,16 @@ Linux I2C slave interface description
 
 by Wolfram Sang <wsa@sang-engineering.com> in 2014-15
 
-Linux can also be an I2C slave in case I2C controllers have slave support.
-Besides this HW requirement, one also needs a software backend providing the
-actual functionality. An example for this is the slave-eeprom driver, which
-acts as a dual memory driver. While another I2C master on the bus can access it
-like a regular EEPROM, the Linux I2C slave can access the content via sysfs and
-retrieve/provide information as needed. The software backend driver and the I2C
-bus driver communicate via events. Here is a small graph visualizing the data
-flow and the means by which data is transported. The dotted line marks only one
-example. The backend could also use e.g. a character device, be in-kernel
-only, or something completely different:
+Linux can also be an I2C slave if the I2C controller in use has slave
+functionality. For that to work, one needs slave support in the bus driver plus
+a hardware independent software backend providing the actual functionality. An
+example for the latter is the slave-eeprom driver, which acts as a dual memory
+driver. While another I2C master on the bus can access it like a regular
+EEPROM, the Linux I2C slave can access the content via sysfs and handle data as
+needed. The backend driver and the I2C bus driver communicate via events. Here
+is a small graph visualizing the data flow and the means by which data is
+transported. The dotted line marks only one example. The backend could also
+use a character device, be in-kernel only, or something completely different:
 
 
               e.g. sysfs        I2C slave events        I/O registers
@@ -31,10 +31,13 @@ User manual
 ===========
 
 I2C slave backends behave like standard I2C clients. So, you can instantiate
-them as described in the document 'instantiating-devices'. A quick example for
-instantiating the slave-eeprom driver from userspace at address 0x64 on bus 1:
+them as described in the document 'instantiating-devices'. The only difference
+is that i2c slave backends have their own address space. So, you have to add
+0x1000 to the address you would originally request. An example for
+instantiating the slave-eeprom driver from userspace at the 7 bit address 0x64
+on bus 1:
 
-  # echo slave-24c02 0x64 > /sys/bus/i2c/devices/i2c-1/new_device
+  # echo slave-24c02 0x1064 > /sys/bus/i2c/devices/i2c-1/new_device
 
 Each backend should come with separate documentation to describe its specific
 behaviour and setup.
@@ -43,6 +46,11 @@ behaviour and setup.
 Developer manual
 ================
 
+First, the events which are used by the bus driver and the backend will be
+described in detail. After that, some implementation hints for extending bus
+drivers and writing backends will be given.
+
+
 I2C slave events
 ----------------