media: ti: j721e-csi2rx: Support system suspend using pm_notifier

As this device is the "orchestrator" for the rest of the media
pipeline, we need to stop all on-going streams before system suspend and
enable them back when the system wakes up from sleep.

Using .suspend/.resume callbacks does not work, as the order of those
callbacks amongst various devices in the camera pipeline like the sensor,
FPD serdes, CSI bridge etc. is impossible to enforce, even with
device links. For example, the Cadence CSI bridge is a child device of
this device, thus we cannot create a device link with the CSI bridge as
a provider and this device as consumer. This can lead to situations
where all the dependencies for the bridge have not yet resumed when we
request the subdev to start streaming again through the .resume callback
defined in this device.

Instead here we register a notifier callback with the PM framework
which is triggered when the system is fully functional. At this point we
can cleanly stop or start the streams, because we know all other devices
and their dependencies are functional. A downside of this approach is
that the userspace is also alive (not frozen yet, or just thawed), so
the suspend notifier might complete before the userspace has completed
all ioctls, like QBUF/DQBUF/STREAMON/STREAMOFF.

Tested-by: Rishikesh Donadkar <r-donadkar@ti.com>
Reviewed-by: Rishikesh Donadkar <r-donadkar@ti.com>
Signed-off-by: Jai Luthra <jai.luthra@ideasonboard.com>
Signed-off-by: Rishikesh Donadkar <r-donadkar@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

0 files changed, 0 insertions, 0 deletions