linux-kernel - Re: [PATCH] media: hantro: Support H264 profile control

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Date:   Sat, 23 Nov 2019 01:00:06 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Nicolas Dufresne <nicolas@...fresne.ca>
Cc:     Hirokazu Honda <hiroh@...omium.org>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        devel@...verdev.osuosl.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: hantro: Support H264 profile control

On Sat, Nov 23, 2019 at 12:09 AM Nicolas Dufresne <nicolas@...fresne.ca> wrote:
>
> Le vendredi 22 novembre 2019 à 14:16 +0900, Hirokazu Honda a écrit :
> > The Hantro G1 decoder supports H.264 profiles from Baseline to High, with
> > the exception of the Extended profile.
> >
> > Expose the V4L2_CID_MPEG_VIDEO_H264_PROFILE control, so that the
> > applications can query the driver for the list of supported profiles.
>
> Thanks for this patch. Do you think we could also add the LEVEL control
> so the profile/level enumeration becomes complete ?
>
> I'm thinking it would be nice if the v4l2 compliance test make sure
> that codecs do implement these controls (both stateful and stateless),
> it's essential for stack with software fallback, or multiple capable
> codec hardware but with different capabilities.
>

Level is a difficult story, because it also specifies the number of
macroblocks per second, but for decoders like this the number of
macroblocks per second it can handle depends on things the driver
might be not aware of - clock frequencies, DDR throughput, system
load, etc.

My take on this is that the decoder driver should advertise the
highest resolution the decoder can handle due to hardware constraints.
Performance related things depend on the integration details and
should be managed elsewhere. For example Android and Chrome OS manage
expected decoding performance in per-board configuration files.

> >
> > Signed-off-by: Hirokazu Honda <hiroh@...omium.org>
> > ---
> >  drivers/staging/media/hantro/hantro_drv.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/staging/media/hantro/hantro_drv.c b/drivers/staging/media/hantro/hantro_drv.c
> > index 6d9d41170832..9387619235d8 100644
> > --- a/drivers/staging/media/hantro/hantro_drv.c
> > +++ b/drivers/staging/media/hantro/hantro_drv.c
> > @@ -355,6 +355,16 @@ static const struct hantro_ctrl controls[] = {
> >                       .def = V4L2_MPEG_VIDEO_H264_START_CODE_ANNEX_B,
> >                       .max = V4L2_MPEG_VIDEO_H264_START_CODE_ANNEX_B,
> >               },
> > +     }, {
> > +             .codec = HANTRO_H264_DECODER,
> > +             .cfg = {
> > +                     .id = V4L2_CID_MPEG_VIDEO_H264_PROFILE,
> > +                     .min = V4L2_MPEG_VIDEO_H264_PROFILE_BASELINE,
> > +                     .max = V4L2_MPEG_VIDEO_H264_PROFILE_HIGH,
> > +                     .menu_skip_mask =
> > +                     BIT(V4L2_MPEG_VIDEO_H264_PROFILE_EXTENDED),
> > +                     .def = V4L2_MPEG_VIDEO_H264_PROFILE_MAIN,
> > +             }
> >       }, {
> >       },
> >  };
>