On Thu, Jan 09, 2014 at 09:49:54PM +0000, David Howells wrote:
> Add tracepoints into the I2C message transfer function to retrieve the message
> sent or received.  The following config options must be turned on to make use
> of the facility:
> 
> 	CONFIG_FTRACE
> 	CONFIG_ENABLE_DEFAULT_TRACERS
> 
> The I2C tracepoint can be enabled thusly:
> 
> 	echo 1 >/sys/kernel/debug/tracing/events/i2c/i2c_transfer/enable
> 
> and will dump messages that can be viewed in /sys/kernel/debug/tracing/trace
> that look like:
> 
> 	... i2c_write: i2c-5 #0 f=00 a=44 l=2 [0214]
> 	... i2c_read: i2c-5 #1 f=01 a=44 l=4
> 	... i2c_reply: i2c-5 #1 f=01 a=44 l=4 [33000000]
> 	... i2c_result: i2c-5 n=2 ret=2
> 
> formatted as:
> 
> 	i2c-<adapter-nr>
> 	#<message-array-index>
> 	f=<flags>
> 	a=<addr>
> 	l=<datalen>
> 	n=<message-array-size>
> 	ret=<result>
> 	[<data>]
> 
> The operation is done between the i2c_write/i2c_read lines and the i2c_reply
> and i2c_result lines so that if the hardware hangs, the trace buffer can be
> consulted to determine the problematic operation.
> 
> The adapters to be traced can be selected by something like:
> 
> 	echo adapter_nr==1 >/sys/kernel/debug/tracing/events/i2c/filter
> 
> These changes are based on code from Steven Rostedt.
> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

Thanks for doing this, much appreciated. One of the first things I'll
review (and play with) next. But hey, has nobody else checked this out
by now? Tested-by or acks very welcome.

Thanks,

   Wolfram