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

[Nicolas Dufresne <nicolas.dufresne@collabora.com>]

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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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