linux-kernel - Re: [PATCH 2/9] media: rkvdec: h264: Fix reference frame

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Message-ID: <151c4930973dbec938f2e1ff135149f40e4cc7de.camel@collabora.com>
Date:   Fri, 03 Jul 2020 00:01:17 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     Jonas Karlman <jonas@...boo.se>, linux-media@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...labora.com>
Cc:     Hans Verkuil <hans.verkuil@...co.com>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Alexandre Courbot <acourbot@...omium.org>
Subject: Re: [PATCH 2/9] media: rkvdec: h264: Fix reference frame_num wrap
 for second field

+Boris

On Wed, 2020-07-01 at 21:56 +0000, Jonas Karlman wrote:
> When decoding the second field in a complementary field pair the second
> field is sharing the same frame_num with the first field.
> 
> Currently the frame_num for the first field is wrapped when it matches the
> field being decoded, this cause issues to decode the second field in a
> complementary field pair.
> 
> Fix this by using inclusive comparison, less than or equal.
> 
> Signed-off-by: Jonas Karlman <jonas@...boo.se>
> ---
>  drivers/staging/media/rkvdec/rkvdec-h264.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/media/rkvdec/rkvdec-h264.c b/drivers/staging/media/rkvdec/rkvdec-h264.c
> index 7b66e2743a4f..f0cfed84d60d 100644
> --- a/drivers/staging/media/rkvdec/rkvdec-h264.c
> +++ b/drivers/staging/media/rkvdec/rkvdec-h264.c
> @@ -754,7 +754,7 @@ static void assemble_hw_rps(struct rkvdec_ctx *ctx,
>  			continue;
>  

Taking a closer look here, I see this comment:

        /*
         * Assign an invalid pic_num if DPB entry at that position is inactive.
         * If we assign 0 in that position hardware will treat that as a real
         * reference picture with pic_num 0, triggering output picture
         * corruption.
         */

ChromeOS driver was setting 0xff on a non-active hw_rps table entry,
but we are not doing so.

Are we missing anything, or is this not really required
(and so the comment is outdated)?

Thanks,
Ezequiel

>  		if (dpb[i].flags & V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM ||
> -		    dpb[i].frame_num < sl_params->frame_num) {
> +		    dpb[i].frame_num <= sl_params->frame_num) {
>  			p[i] = dpb[i].frame_num;
>  			continue;
>  		}