linux-kernel - [PATCH v2 05/14] media: uapi: h264: Increase size of 'first_mb_in

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Message-Id: <20200806151310.98624-6-ezequiel@collabora.com>
Date:   Thu,  6 Aug 2020 12:13:01 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Tomasz Figa <tfiga@...omium.org>, kernel@...labora.com,
        Jonas Karlman <jonas@...boo.se>,
        Hans Verkuil <hverkuil@...all.nl>,
        Alexandre Courbot <acourbot@...omium.org>,
        Jeffrey Kardatzke <jkardatzke@...omium.org>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Maxime Ripard <mripard@...nel.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Ezequiel Garcia <ezequiel@...labora.com>
Subject: [PATCH v2 05/14] media: uapi: h264: Increase size of 'first_mb_in_slice' field

Slice header syntax element 'first_mb_in_slice' can point
to the last macroblock, currently the field can only reference
65536 macroblocks which is insufficient for 8K videos.

Although unlikely, a 8192x4320 video (where macroblocks are 16x16),
would contain 138240 macroblocks on a frame.

As per the H264 specification, 'first_mb_in_slice' can be up to
PicSizeInMbs - 1, so increase the size of the field to 32-bits.

Note that v4l2_ctrl_h264_slice_params struct will be modified
in a follow-up commit, and so we defer its 64-bit padding.

Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
---
 Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 2 +-
 include/media/h264-ctrls.h                                | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
index e4dec3f9b71a..141c9249d528 100644
--- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
+++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
@@ -1774,7 +1774,7 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
     * - __u32
       - ``header_bit_size``
       -
-    * - __u16
+    * - __u32
       - ``first_mb_in_slice``
       -
     * - __u8
diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
index 54cd9bec0b23..66327ca55088 100644
--- a/include/media/h264-ctrls.h
+++ b/include/media/h264-ctrls.h
@@ -167,7 +167,8 @@ struct v4l2_ctrl_h264_slice_params {
 	/* Offset in bits to slice_data() from the beginning of this slice. */
 	__u32 header_bit_size;
 
-	__u16 first_mb_in_slice;
+	__u32 first_mb_in_slice;
+
 	__u8 slice_type;
 	__u8 pic_parameter_set_id;
 	__u8 colour_plane_id;
-- 
2.27.0