Re: [RFC 4/7] media: uapi: h264: increase size of fields

Nicolas Dufresne
2020-06-25T15:01:28Z

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Le mardi 23 juin 2020 à 15:28 -0300, Ezequiel Garcia a écrit :
> 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.
>
> DPB entry PicNum maximum value is 2*MaxFrameNum for interlaced
> content (field_pic_flag=1).
>
> Therefore, increase 'first_mb_in_slice' and 'pic_num'.
>
> The v4l2_h264_dpb_entry struct needs to be padded to avoid a hole,
> which will be useful to allow future uAPI extensions.
>
> Note that v4l2_ctrl_h264_slice_params struct will be modified
> in a follow-up commit, and so we defer its 64-bit padding.

This patch includes two changes, with two distinct rationale. Please
split in two, I would also add reference to the spec in the commit
messages. The explanation is also insufficient. Need to mention that
macro-blocks are 16x16, and the bounds for synthetic value
MaxFrameNum (derived from bitstream value) has not be mention either.

>
> Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
> ---
> .../userspace-api/media/v4l/ext-ctrls-codec.rst | 7 +++++--
> drivers/media/v4l2-core/v4l2-ctrls.c | 9 +++++++++
> include/media/h264-ctrls.h | 6 ++++--
> include/media/v4l2-h264.h | 2 +-
> 4 files changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index 0808a36777b6..e3b5a28fb965 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -1772,7 +1772,7 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> * - __u32
> - ``header_bit_size``
> -
> - * - __u16
> + * - __u32
> - ``first_mb_in_slice``
> -
> * - __u8
> @@ -2046,7 +2046,10 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> * - __u16
> - ``frame_num``
> -
> - * - __u16
> + * - __u8
> + - ``reserved[6]``
> + - Applications and drivers must set this to zero.
> + * - __u32
> - ``pic_num``
> -
> * - __s32
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index 6abd023f10c7..a751c14f9c22 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -1734,6 +1734,7 @@ static int std_validate_compound(const struct v4l2_ctrl *ctrl, u32 idx,
> struct v4l2_ctrl_mpeg2_slice_params *p_mpeg2_slice_params;
> struct v4l2_ctrl_vp8_frame_header *p_vp8_frame_header;
> struct v4l2_ctrl_h264_slice_params *p_h264_slice_params;
> + struct v4l2_ctrl_h264_decode_params *p_h264_dec_params;
> struct v4l2_ctrl_hevc_sps *p_hevc_sps;
> struct v4l2_ctrl_hevc_pps *p_hevc_pps;
> struct v4l2_ctrl_hevc_slice_params *p_hevc_slice_params;
> @@ -1808,6 +1809,14 @@ static int std_validate_compound(const struct v4l2_ctrl *ctrl, u32 idx,
> }
> break;
> case V4L2_CTRL_TYPE_H264_DECODE_PARAMS:
> + p_h264_dec_params = p;
> +
> + for (i = 0; i < V4L2_H264_NUM_DPB_ENTRIES; i++) {
> + struct v4l2_h264_dpb_entry *dpb_entry =
> + &p_h264_dec_params->dpb[i];
> +
> + zero_reserved(*dpb_entry);
> + }
> break;
>
> case V4L2_CTRL_TYPE_VP8_FRAME_HEADER:
> diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> index c6cbf178c1c9..a938d16b901c 100644
> --- a/include/media/h264-ctrls.h
> +++ b/include/media/h264-ctrls.h
> @@ -161,7 +161,8 @@ 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;
> @@ -208,7 +209,8 @@ struct v4l2_ctrl_h264_slice_params {
> struct v4l2_h264_dpb_entry {
> __u64 reference_ts;
> __u16 frame_num;
> - __u16 pic_num;
> + __u8 reserved[6];
> + __u32 pic_num;
> /* Note that field is indicated by v4l2_buffer.field */
> __s32 top_field_order_cnt;
> __s32 bottom_field_order_cnt;
> diff --git a/include/media/v4l2-h264.h b/include/media/v4l2-h264.h
> index bc9ebb560ccf..1a5f26fc2a9a 100644
> --- a/include/media/v4l2-h264.h
> +++ b/include/media/v4l2-h264.h
> @@ -33,7 +33,7 @@ struct v4l2_h264_reflist_builder {
> struct {
> s32 pic_order_count;
> int frame_num;
> - u16 pic_num;
> + u32 pic_num;
> u16 longterm : 1;
> } refs[V4L2_H264_NUM_DPB_ENTRIES];
> s32 cur_pic_order_count;

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