The DISCOM calculates a CRC on a configurable window of the frame. It
interfaces to the VSP through the UIF glue, hence the name used in the
code.

The module supports configuration of the CRC window through the crop
rectangle on the sink pad of the corresponding entity. However, unlike
the traditional V4L2 subdevice model, the crop rectangle does not
influence the format on the source pad.

Modeling the DISCOM as a sink-only entity would allow adhering to the
V4L2 subdevice model at the expense of more complex code in the driver,
as at the hardware level the UIF is handled as a sink+source entity. As
the DISCOM is only present in R-Car Gen3 VSP-D and VSP-DL instances it
is not exposed to userspace through V4L2 but controlled through the DU
driver. We can thus change this model later if needed without fear of
affecting userspace.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>