SFC (Scaler & Format Converter) units are shared between VD and VEBoxes.
They also happen to have separate reset bits. So, whenever we want to reset
one or more of the media engines, we have to make sure the SFCs do not
change owner in the process and, if this owner happens to be one of the
engines being reset, we need to reset the SFC as well.

This happens in 4 steps:

1) Tell the engine that a software reset is going to happen. The engine
will then try to force lock the SFC (if currently locked, it will
remain so; if currently unlocked, it will ignore this and all new lock
requests).

2) Poll the ack bit to make sure the hardware has received the forced
lock from the driver. Once this bit is set, it indicates SFC status
(lock or unlock) will not change anymore (until we tell the engine it
is safe to unlock again).

3) Check the usage bit to see if the SFC has ended up being locked to
the engine we want to reset. If this is the case, we have to reset
the SFC as well.

4) Unlock all the SFCs once the reset sequence is completed.

Obviously, if we are resetting the whole GPU, we don't have to worry
about all of this.

BSpec: 10989
BSpec: 10990
BSpec: 10954
BSpec: 10955
BSpec: 10956
BSpec: 19212
Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181213091522.2926-4-chris@chris-wilson.co.uk