Hi Niklas,
There seems to be a race in rcar-v4l2.c, causing
WARN_ON(entity->use_count < 0) in pipeline_pm_power_one().
If my understanding is correct, the VIN v4l2 nodes are being created
(rvin_v4l2_register), meaning they are userspace accessible, but the
media pipeline as a whole is not ready yet (e.g. media links).
So what happens is that after some video nodes have been created, the
userspace opens them (I think it's udevd checking the new device nodes),
causing rvin_open(). rvin_open() goes through the media graph and does
some PM enabling (I'm not familiar with the legacy
v4l2_pipeline_pm_get()). However, as the links are not there, it doesn't
really enable much at all.
Then the driver goes forward and finishes with the media graph.
Then the userspace closes the opened video nodes, rvin_release() gets
called and it goes through the media graph, which now contains all the
entities, and powers them down. As the entities were never powered up,
we hit the use_count warning.
This happens quite often to me when loading the modules, but I think it
can be made to happen more often by adding msleep(1000) to the beginning
of rvin_release(), thus ensuring that the graph setup is finished before
the rvin_release() proceeds (and hoping that the graph setup was not
ready when rvin_open() was called).
Tomi
