linux-kernel - [PATCH v4 01/24] media: doc: Document dual use of H.264 pic_num/frame

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Message-Id: <20220426125751.108293-2-nicolas.dufresne@collabora.com>
Date:   Tue, 26 Apr 2022 08:57:27 -0400
From:   Nicolas Dufresne <nicolas.dufresne@...labora.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     nicolas@...fresne.ca, linux-media@...r.kernel.org,
        Sebastian Fricke <sebastian.fricke@...labora.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 01/24] media: doc: Document dual use of H.264 pic_num/frame_num

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@...labora.com>
Reviewed-by: Sebastian Fricke <sebastian.fricke@...labora.com>
---
 .../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>`
-- 
2.34.1