Re: [PATCH v3 01/19] media: uapi: h264: Update reference lists

From: Hans Verkuil
Date: Thu Aug 20 2020 - 05:11:53 EST

On 14/08/2020 15:36, Ezequiel Garcia wrote:
> From: Jernej Skrabec <jernej.skrabec@xxxxxxxx>
>
> When dealing with with interlaced frames, reference lists must tell if
> each particular reference is meant for top or bottom field. This info
> is currently not provided at all in the H264 related controls.
>
> Make reference lists hold a structure which will also hold an
> enumerator type along index into DPB array. The enumerator must
> be used to specify if reference is for top or bottom field.
>
> Currently the only user of these lists is Cedrus which is just compile
> fixed here. Actual usage of will come in a following commit.
>
> Signed-off-by: Jernej Skrabec <jernej.skrabec@xxxxxxxx>
> Signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
> ---
> v3:
> * Rename to avoid mentioning the DPB.
> v2:
> * As pointed out by Jonas, enum v4l2_h264_dpb_reference here.
> ---
> .../media/v4l/ext-ctrls-codec.rst | 44 ++++++++++++++++++-
> .../staging/media/sunxi/cedrus/cedrus_h264.c | 6 +--
> include/media/h264-ctrls.h | 23 +++++++---
> 3 files changed, 62 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index d0d506a444b1..b9b2617c3bda 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -1843,10 +1843,10 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> * - __u32
> - ``slice_group_change_cycle``
> -
> - * - __u8
> + * - struct :c:type:`v4l2_h264_reference`
> - ``ref_pic_list0[32]``
> - Reference picture list after applying the per-slice modifications
> - * - __u8
> + * - struct :c:type:`v4l2_h264_reference`
> - ``ref_pic_list1[32]``
> - Reference picture list after applying the per-slice modifications
> * - __u32
> @@ -1926,6 +1926,46 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> - ``chroma_offset[32][2]``
> -
>
> +``Picture Reference``
> +
> +.. c:type:: v4l2_h264_reference
> +
> +.. cssclass:: longtable
> +
> +.. flat-table:: struct v4l2_h264_reference
> + :header-rows: 0
> + :stub-columns: 0
> + :widths: 1 1 2
> +
> + * - enum :c:type:`v4l2_h264_field_reference`
> + - ``reference``
> + - Specifies how the picture is referenced.
> + * - __u8
> + - ``index``
> + - Index into the :c:type:`v4l2_ctrl_h264_decode_params`.dpb array.
> +
> +.. c:type:: v4l2_h264_field_reference
> +
> +.. cssclass:: longtable
> +
> +.. flat-table::
> + :header-rows: 0
> + :stub-columns: 0
> + :widths: 1 1 2
> +
> + * - ``V4L2_H264_TOP_FIELD_REF``
> + - 0x1
> + - The top field in field pair is used for
> + short-term reference.
> + * - ``V4L2_H264_BOTTOM_FIELD_REF``
> + - 0x2
> + - The bottom field in field pair is used for
> + short-term reference.
> + * - ``V4L2_H264_FRAME_REF``
> + - 0x3
> + - The frame (or the top/bottom fields, if it's a field pair)
> + is used for short-term reference.
> +
> ``V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS (struct)``
> Specifies the decode parameters (as extracted from the bitstream)
> for the associated H264 slice data. This includes the necessary
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> index 54ee2aa423e2..cce527bbdf86 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> @@ -166,8 +166,8 @@ static void cedrus_write_frame_list(struct cedrus_ctx *ctx,
>
> static void _cedrus_write_ref_list(struct cedrus_ctx *ctx,
> struct cedrus_run *run,
> - const u8 *ref_list, u8 num_ref,
> - enum cedrus_h264_sram_off sram)
> + const struct v4l2_h264_reference *ref_list,
> + u8 num_ref, enum cedrus_h264_sram_off sram)
> {
> const struct v4l2_ctrl_h264_decode_params *decode = run->h264.decode_params;
> struct vb2_queue *cap_q;
> @@ -188,7 +188,7 @@ static void _cedrus_write_ref_list(struct cedrus_ctx *ctx,
> int buf_idx;
> u8 dpb_idx;
>
> - dpb_idx = ref_list[i];
> + dpb_idx = ref_list[i].index;
> dpb = &decode->dpb[dpb_idx];
>
> if (!(dpb->flags & V4L2_H264_DPB_ENTRY_FLAG_ACTIVE))
> diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> index 080fd1293c42..5f635e8d25e2 100644
> --- a/include/media/h264-ctrls.h
> +++ b/include/media/h264-ctrls.h
> @@ -19,6 +19,8 @@
> */
> #define V4L2_H264_NUM_DPB_ENTRIES 16
>
> +#define V4L2_H264_REF_LIST_LEN (2 * V4L2_H264_NUM_DPB_ENTRIES)
> +
> /* Our pixel format isn't stable at the moment */
> #define V4L2_PIX_FMT_H264_SLICE v4l2_fourcc('S', '2', '6', '4') /* H264 parsed slices */
>
> @@ -140,6 +142,19 @@ struct v4l2_h264_pred_weight_table {
> #define V4L2_H264_SLICE_FLAG_DIRECT_SPATIAL_MV_PRED 0x04
> #define V4L2_H264_SLICE_FLAG_SP_FOR_SWITCH 0x08
>
> +enum v4l2_h264_field_reference {
> + V4L2_H264_TOP_FIELD_REF = 0x1,
> + V4L2_H264_BOTTOM_FIELD_REF = 0x2,
> + V4L2_H264_FRAME_REF = 0x3,
> +};
> +
> +struct v4l2_h264_reference {
> + enum v4l2_h264_field_reference fields;
> +
> + /* Index into v4l2_ctrl_h264_decode_params.dpb[] */
> + __u8 index;
> +};

This introducing 3 bytes of padding at the end of this struct...

> +
> struct v4l2_ctrl_h264_slice_params {
> /* Size in bytes, including header */
> __u32 size;
> @@ -178,12 +193,8 @@ struct v4l2_ctrl_h264_slice_params {
> __u8 num_ref_idx_l1_active_minus1;
> __u32 slice_group_change_cycle;
>
> - /*
> - * Entries on each list are indices into
> - * v4l2_ctrl_h264_decode_params.dpb[].
> - */
> - __u8 ref_pic_list0[32];
> - __u8 ref_pic_list1[32];
> + struct v4l2_h264_reference ref_pic_list0[V4L2_H264_REF_LIST_LEN];
> + struct v4l2_h264_reference ref_pic_list1[V4L2_H264_REF_LIST_LEN];

...which leads to a lot of holes of uninitialized data in these arrays.

I recommend to replace 'enum v4l2_h264_field_reference fields;' in struct v4l2_h264_reference
by '__u8 fields; /* enum v4l2_h264_field_reference */'.

This also saves a lot of memory (2*32*6 = 384 bytes!) and avoids the padding issue.

Regards,

Hans

>
> __u32 flags;
> };
>