linux-kernel - Re: [PATCH v2] media: mediatek: vcodec: fix h264 cavlc bitstream fail

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Date:   Mon, 14 Nov 2022 12:08:37 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Yunfei Dong <yunfei.dong@...iatek.com>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Nicolas Dufresne <nicolas@...fresne.ca>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        Tiffany Lin <tiffany.lin@...iatek.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        George Sun <george.sun@...iatek.com>,
        Xiaoyong Lu <xiaoyong.lu@...iatek.com>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Fritz Koenig <frkoenig@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Steve Cho <stevecho@...omium.org>, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v2] media: mediatek: vcodec: fix h264 cavlc bitstream fail

Il 18/10/22 13:41, Yunfei Dong ha scritto:
> Some cavlc bistream will decode fail when the frame size is small than

s/small/smaller/g

> 20 bytes. Need to add pending data at the end of the bitstream.
> 
> For the minimum size of mapped memory is 256 bytes(16x16), adding four bytes data
> won't lead to access unknown virtual memory.
> 
> Fixes: 59fba9eed5a7 ("media: mediatek: vcodec: support stateless H.264 decoding for mt8192")
> Signed-off-by: Yunfei Dong <yunfei.dong@...iatek.com>
> ---
> compared with v1:
> - add detail comments for function: vdec_h264_insert_startcode.
> - re-write commit message.
> ---
>   .../vcodec/vdec/vdec_h264_req_multi_if.c      | 32 +++++++++++++++++--
>   1 file changed, 29 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..18e048755d11 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 +539,29 @@ 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;
> +
> +	/* Need to add pending data at the end of bitstream when bs_sz is small than
> +	 * 20 bytes for cavlc bitstream, or lat will decode fail. This pending data is
> +	 * useful for mt8192 and mt8195 platform.

What is the reason why other SoCs don't need this?

> +	 *
> +	 * 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")))

I'm not comfortable seeing of_device_is_compatible... this list will grow whenever
a new SoC needing this appears.
Please think about a good name for a flag/quirk, or a bool, in the platform data
for these two SoCs and use it.

Regards,
Angelo