Hi Laurent,

On Sat, 2021-01-09 at 03:09 +0200, Laurent Pinchart wrote:

Could you elaborate a little bit here ? We don't have an API to
explicitly enumerate supported interlacing types. This can be done by
calling VIDIOC_TRY_FMT with all field types and see which ones are
supported. You can still do so with the MC-based API, the video node
will return from VIDIOC_TRY_FMT the interlacing types intrinsicly
supported by the video node, and you can query from the source subdev
the interlacing types supported by the source. Userspace can then
combine the information to find what is supported.

The i.MX6 CSI always captures whole frames, so SEQ_TB or SEQ_BT at its
source pad.
The IDMAC supports "interlaced scan" of SEQ_TB into INTERLACED_TB and
SEQ_BT into INTERLACED_BT when writing to memory. It can't change the
field timing order (BT <-> TB) as that was already decided at the CSI.

So for capture of interlaced material, the video device currently allows
either SEQ_TB and INTERLACED_TB or SEQ_BT and INTERLACED_BT, depending
on which field order is configured at the CSI source pad.

See d969291d8479 ("media: imx: Fix field negotiation") for details.

regards
Philipp