The userspace needs a way to match received metadata buffers to pixel
data buffers. The obvious way to do this is to use the CSI-2 frame
number, as both the metadata and the pixel data have the same frame
number as they come from the same frame.

However, we don't have means to convey the frame number to userspace. We
do have the 'sequence' field, which with a few tricks can be used for
this purpose.

To achieve this, track the frame number for each virtual channel and
increase the sequence for each virtual channel by frame-number -
previous-frame-number, also taking into account the eventual wrap of the
CSI-2 frame number. If the CSI-2 peripheral does not support frame
numbers, CAL increases the frame number register by one each frame.

This way we get a monotonically increasing sequence number which is
common to all streams using the same virtual channel.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>