Event Tracing

Tracing I2C Events

Note: I am assuming that debugfs is mounted under /sys/kernel/debug

If not, try:

mount -t debugfs none /sys/kernel/debug

Change into the tracing directory:

cd /sys/kernel/debug/tracing/

Make sure the function tracer is disabled:

echo nop > current_tracer

Enable all I2C events:

echo 1 > events/i2c/enable

Make sure tracing is enabled:

echo 1 > tracing_on

The trace messages can be viewed in /sys/kernel/debug/tracing/trace, example:

... i2c_write: i2c-5 #0 a=044 f=0000 l=2 [02-14]
... i2c_read: i2c-5 #1 a=044 f=0001 l=4
... i2c_reply: i2c-5 #1 a=044 f=0001 l=4 [33-00-00-00]
... i2c_result: i2c-5 n=2 ret=2

The trace events user-space API documentation can be found in the file Documentation/trace/events.txt of the kernel source.