[PATCH v4 01/24] media: doc: Document dual use of H.264 pic_num/frame_num

From: Nicolas Dufresne
Date: Tue Apr 26 2022 - 08:58:16 EST

These two fields need documentation as they have dual meaning. It is also
confusing since pic_num is a derived value from frame_num, so this should
help application developers. If we ever need to make a V2 of this API, I
would suggest to remove pic_num entirely.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@xxxxxxxxxxxxx>
Reviewed-by: Sebastian Fricke <sebastian.fricke@xxxxxxxxxxxxx>
.../media/v4l/ext-ctrls-codec-stateless.rst | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
index 6541e4c32b26..bee73065e993 100644
--- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
+++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
@@ -649,10 +649,16 @@ Stateless Codec Control ID
:c:type:`timeval` in struct :c:type:`v4l2_buffer` to a __u64.
* - __u32
- ``pic_num``
- -
+ - For short term references, this must match the derived value PicNum
+ (8-28) and for long term references it must match the derived value
+ LongTermPicNum (8-29). When decoding frames (as opposed to fields)
+ pic_num is the same as FrameNumWrap.
* - __u16
- ``frame_num``
- -
+ - For short term references, this must match the frame_num value from
+ the slice header syntax (the driver will wrap the value if needed). For
+ long term references, this must be set to the value of
+ long_term_frame_idx described in the dec_ref_pic_marking() syntax.
* - __u8
- ``fields``
- Specifies how the DPB entry is referenced. See :ref:`Reference Fields <h264_ref_fields>`