media: debugfs-cec-error-inj: document CEC error inj debugfs ABI

Document the core of the debugfs CEC error injection ABI.

The driver specific commands are documented elsewhere and
this file points to that documentation.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/ABI/testing/debugfs-cec-error-inj

+What:		/sys/kernel/debug/cec/*/error-inj
+Date:		March 2018
+Contact:	Hans Verkuil <hans.verkuil@cisco.com>
+Description:
+
+The CEC Framework allows for CEC error injection commands through
+debugfs. Drivers that support this will create an error-inj file
+through which the error injection commands can be given.
+
+The basic syntax is as follows:
+
+Leading spaces/tabs are ignored. If the next character is a '#' or the
+end of the line was reached, then the whole line is ignored. Otherwise
+a command is expected.
+
+It is up to the driver to decide what commands to implement. The only
+exception is that the command 'clear' without any arguments must be
+implemented and that it will remove all current error injection
+commands.
+
+This ensures that you can always do 'echo clear >error-inj' to clear any
+error injections without having to know the details of the driver-specific
+commands.
+
+Note that the output of 'error-inj' shall be valid as input to 'error-inj'.
+So this must work:
+
+	$ cat error-inj >einj.txt
+	$ cat einj.txt >error-inj
+
+Other than these basic rules described above this ABI is not considered
+stable and may change in the future.
+
+Drivers that implement this functionality must document the commands as
+part of the CEC documentation and must keep that documentation up to date
+when changes are made.
+
+The following CEC error injection implementations exist:
+
+- Documentation/media/uapi/cec/cec-pin-error-inj.rst

MAINTAINERS

@@ -3307,6 +3307,7 @@ F:	include/media/cec-notifier.h
 F:	include/uapi/linux/cec.h
 F:	include/uapi/linux/cec-funcs.h
 F:	Documentation/devicetree/bindings/media/cec.txt
+F:	Documentation/ABI/testing/debugfs-cec-error-inj
 
 CEC GPIO DRIVER
 M:	Hans Verkuil <hans.verkuil@cisco.com>