media: vsp1: Document max_width restriction on UDS

The UDS is currently restricted based on a partition size of 256 pixels.
Document the actual restrictions, but don't increase the implementation.

The extended partition algorithm may later choose to utilise a larger
partition size to support overlapping partitions which will improve the
quality of the output images.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

diff --git a/drivers/media/platform/vsp1/vsp1_uds.c b/drivers/media/platform/vsp1/vsp1_uds.c
index 75c613050151996fa5af48a3d690482b4ea490f3..27012af973b24b78897f6766174a1def21812a0b 100644 (file)
--- a/drivers/media/platform/vsp1/vsp1_uds.c
+++ b/drivers/media/platform/vsp1/vsp1_uds.c
@@ -342,6 +342,14 @@ static unsigned int uds_max_width(struct vsp1_entity *entity,
                                            UDS_PAD_SOURCE);
        hscale = output->width / input->width;
 
+       /*
+        * The maximum width of the UDS is 304 pixels. These are input pixels
+        * in the event of up-scaling, and output pixels in the event of
+        * downscaling.
+        *
+        * To support overlapping partition windows we clamp at units of 256 and
+        * the remaining pixels are reserved.
+        */
        if (hscale <= 2)
                return 256;
        else if (hscale <= 4)