Re: [PATCH] media: mediatek: vcodec: fix h264 cavlc bitstream fail

[Chen-Yu Tsai]

On Mon, Oct 17, 2022 at 5:02 PM Yunfei Dong <yunfei.dong@xxxxxxxxxxxx> wrote:
>
> Some cavlc bistream will decode fail when the frame size is small than
> 20 bytes. Need to add pending data at the end of the bitstream.

"magic terminating pattern" instead of "pending data"?

> For the size of mapped memory is at least one page, adding four bytes data
> won't lead to access unknown virtual memory.

Actually we can narrow this down a bit. The minimum dimension (16x16)
sets the minimum size of the buffer at 256 bytes.

> Fixes: 59fba9eed5a7 ("media: mediatek: vcodec: support stateless H.264 decoding for mt8192")
> Signed-off-by: Yunfei Dong <yunfei.dong@xxxxxxxxxxxx>
> ---
>  .../vcodec/vdec/vdec_h264_req_multi_if.c      | 27 ++++++++++++++++---
>  1 file changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c b/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c
> index 4cc92700692b..c1583dddcb04 100644
> --- a/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c
> +++ b/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c
> @@ -539,6 +539,24 @@ static int vdec_h264_slice_core_decode(struct vdec_lat_buf *lat_buf)
>         return 0;
>  }
>
> +static void vdec_h264_insert_startcode(struct mtk_vcodec_dev *vcodec_dev, unsigned char *buf,
> +                                      size_t *bs_size, struct mtk_h264_pps_param *pps)
> +{
> +       struct device *dev = &vcodec_dev->plat_dev->dev;
> +
> +       /* cavlc bitstream when entropy_coding_mode_flag is false. */
> +       if (pps->entropy_coding_mode_flag || *bs_size > 20 ||
> +           !(of_device_is_compatible(dev->of_node, "mediatek,mt8192-vcodec-dec") ||
> +           of_device_is_compatible(dev->of_node, "mediatek,mt8195-vcodec-dec")))
> +               return;
> +

There should be a comment here describing what is added.


ChenYu

> +       buf[*bs_size] = 0;
> +       buf[*bs_size + 1] = 0;
> +       buf[*bs_size + 2] = 1;
> +       buf[*bs_size + 3] = 0xff;
> +       (*bs_size) += 4;
> +}
> +
>  static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
>                                       struct vdec_fb *fb, bool *res_chg)
>  {
> @@ -582,9 +600,6 @@ static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
>         }
>
>         inst->vsi->dec.nal_info = buf[nal_start_idx];
> -       inst->vsi->dec.bs_buf_addr = (u64)bs->dma_addr;
> -       inst->vsi->dec.bs_buf_size = bs->size;
> -
>         lat_buf->src_buf_req = src_buf_info->m2m_buf.vb.vb2_buf.req_obj.req;
>         v4l2_m2m_buf_copy_metadata(&src_buf_info->m2m_buf.vb, &lat_buf->ts_info, true);
>
> @@ -592,6 +607,12 @@ static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
>         if (err)
>                 goto err_free_fb_out;
>
> +       vdec_h264_insert_startcode(inst->ctx->dev, buf, &bs->size,
> +                                  &share_info->h264_slice_params.pps);
> +
> +       inst->vsi->dec.bs_buf_addr = (uint64_t)bs->dma_addr;
> +       inst->vsi->dec.bs_buf_size = bs->size;
> +
>         *res_chg = inst->resolution_changed;
>         if (inst->resolution_changed) {
>                 mtk_vcodec_debug(inst, "- resolution changed -");
> --
> 2.25.1
>