[media] vivid: do not allow video loopback for SEQ_TB/BT

Sequential top-bottom/bottom-top fields are not supported as video loopback.
This is too much work to implement for field settings that are rarely used.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/video4linux/vivid.txt b/Documentation/video4linux/vivid.txt
index 6cfc8541a362..cd4b5a1ac529 100644
--- a/Documentation/video4linux/vivid.txt
+++ b/Documentation/video4linux/vivid.txt
@@ -912,6 +912,11 @@ looped to the video input provided that:
   sequence and field counting in struct v4l2_buffer on the capture side may not
   be 100% accurate.
 
+- field settings V4L2_FIELD_SEQ_TB/BT are not supported. While it is possible to
+  implement this, it would mean a lot of work to get this right. Since these
+  field values are rarely used the decision was made not to implement this for
+  now.
+
 - on the input side the "Standard Signal Mode" for the S-Video input or the
   "DV Timings Signal Mode" for the HDMI input should be configured so that a
   valid signal is passed to the video input.