linux-kernel - RE: [EXT] Re: [PATCH] media: videobuf2: add V4L2_BUF_FLAG_HEADERS

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Message-ID: <AM6PR04MB6341F861DA6493045F0CE070E71A9@AM6PR04MB6341.eurprd04.prod.outlook.com>
Date:   Wed, 7 Dec 2022 08:49:36 +0000
From:   Ming Qian <ming.qian@....com>
To:     Nicolas Dufresne <nicolas@...fresne.ca>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        "mchehab@...nel.org" <mchehab@...nel.org>
CC:     "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Tomasz Figa <tfiga@...omium.org>
Subject: RE: [EXT] Re: [PATCH] media: videobuf2: add
 V4L2_BUF_FLAG_HEADERS_ONLY flag



>-----Original Message-----
>From: Nicolas Dufresne <nicolas@...fresne.ca>
>Le mardi 06 décembre 2022 à 10:05 +0100, Hans Verkuil a écrit :
>> > For decoders, if a a decoder is in "separate mode", it seems that
>> > sending headers must happen this way. If this uses a separate path
>> > internally, the kernel needs also to be aware which buffers are what
>> > (and we don't parse in the kernel). In very basic case, the driver
>> > assume that the first buffer after streamon is a header, but that
>> > prevents resolution changes without a
>> > drain+flush, which android and chromeos folks seems to use. (I
>> > drain+always drain
>> > and
>> > flush for what I'm doing).
>>
>> OK, thank you for the explanation.
>>
>> So if this is going to be added, then existing drivers that use
>> V4L2_MPEG_VIDEO_HEADER_MODE_SEPARATE have to be adapted to use
>the new
>> flag as well.
>>
>> From what I can tell those are the mediatek vcodec, venus and s5p-mfc
>> encoders.
>> I suspect/hope that it won't be too difficult to add this new flag there.
>
>The exercise will also be very informative for the reviewers, so yes, I would
>ask Ming to update all the drivers, though its fine to only compile test this and
>leave it to the maintainers to verify (at least that's my opinion). I don't see this
>change as a break, as any existing userspace will just ignore this, and maybe
>managed to support it by deep parsing (which will keep working).
>Otherwise, existing userspace using this mode have been broken for
>renegotiation, and that change will not deteriorate (nor improve) the end
>result.
>
>Nicolas
>
>>
>> Regards,
>>
>>       Hans

Hi Hans and Nicolas,
    I'll try to prepare the patch to update all the drivers that needs to apply this flag.
Ming