linux-kernel - Re: [PATCH v6 3/4] media: meson: add v4l2 m2m video decoder driver

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Date:   Mon, 27 May 2019 17:41:14 +0200
From:   Maxime Jourdan <mjourdan@...libre.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH v6 3/4] media: meson: add v4l2 m2m video decoder driver

On Mon, May 27, 2019 at 4:54 PM Hans Verkuil <hverkuil@...all.nl> wrote:
>
> On 5/27/19 4:44 PM, Maxime Jourdan wrote:
> > Hi Hans,
> > On Mon, May 27, 2019 at 12:04 PM Hans Verkuil <hverkuil@...all.nl> wrote:
> >>
> >> Hi Maxime,
> >>
> >> First a high-level comment: I think this driver should go to staging.
> >> Once we finalize the stateful decoder spec, and we've updated the
> >> v4l2-compliance test, then this needs to be tested against that and
> >> only if it passes can it be moved out of staging.
> >>
> >
> > I chose to send the driver supporting only MPEG2 for now as it keeps
> > it "to the point", but as it turns out it's one of the few formats on
> > Amlogic that can't fully respect the spec at the moment because of the
> > lack of support for V4L2_EVENT_SOURCE_CHANGE, thus the patch in the
> > series that adds a new flag V4L2_FMT_FLAG_FIXED_RESOLUTION. It
> > basically requires userspace to set the format (i.e coded resolution)
> > since the driver/fw can't probe it.
> > At the moment, this is described in the v3 spec like this:
> >
> >>
> >> 1. Set the coded format on ``OUTPUT`` via :c:func:`VIDIOC_S_FMT`
> >>
> >>   * **Required fields:**
> >>
> >>     ``type``
> >>         a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``
> >>
> >>     ``pixelformat``
> >>         a coded pixel format
> >>
> >>     ``width``, ``height``
> >>         required only if cannot be parsed from the stream for the given
> >>         coded format; optional otherwise - set to zero to ignore
> >>
> >
> > But MPEG2 being a format where the coded resolution is inside the
> > bitstream, this is purely an Amlogic issue where the firmware doesn't
> > extend the capability to do this.
> >
> > Here's a proposal: if I were to resend the driver supporting only H264
> > and conforming to the spec, would you be considering it for inclusion
> > in the main tree ? Does your current iteration of v4l2-compliance
> > support testing stateful decoders with H264 bitstreams ?
>
> The core problem is that the spec isn't finalized yet. The v3 spec you
> refer to above is old already since there are various changes planned.
>
> If you want to test your driver with a v4l2-compliance that is likely
> to be close to the final version of the spec, then you can use this
> branch:
>
> https://git.linuxtv.org/hverkuil/v4l-utils.git/log/?h=vicodec
>
> You can test with:
>
> v4l2-compliance -s --stream-from <file>
>
> I wouldn't be too worried about keeping it in staging. Having it there
> will already be very nice indeed. Just add a TODO file that states that
> you are waiting for the final version of the stateful decoder spec and
> the corresponding compliance tests.
>
> The V4L2_FMT_FLAG_FIXED_RESOLUTION isn't a blocker. That flag makes sense,
> and so it has nothing to do with keeping this driver in staging.
>

Okay, I understand. I will send a v7 with the driver in
staging+TODO+MAINTAINERS update.

Regards,
Maxime

> Regards,
>
>         Hans
>
<snip>