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Message-ID: <0841fd86ea9bf52057e2a4622a7b9719662cc484.camel@ndufresne.ca>
Subject: Re: [PATCH v4 2/3] media: meson: add v4l2 m2m video decoder driver
From:   Nicolas Dufresne <nicolas@ndufresne.ca>
To:     Hans Verkuil <hverkuil@xs4all.nl>,
        Maxime Jourdan <mjourdan@baylibre.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>
Cc:     Hans Verkuil <hans.verkuil@cisco.com>,
        Kevin Hilman <khilman@baylibre.com>,
        Jerome Brunet <jbrunet@baylibre.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-amlogic@lists.infradead.org
Date:   Fri, 09 Nov 2018 16:21:35 -0500
In-Reply-To: <2f88a17d-76f8-ec70-c18f-aa0d688249be@xs4all.nl>
References: <20181106075926.19269-1-mjourdan@baylibre.com>
         <20181106075926.19269-3-mjourdan@baylibre.com>
         <2f88a17d-76f8-ec70-c18f-aa0d688249be@xs4all.nl>
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Le jeudi 08 novembre 2018 =C3=A0 09:42 +0100, Hans Verkuil a =C3=A9crit :
> > +static int vdec_queue_setup(struct vb2_queue *q,
> > +             unsigned int *num_buffers, unsigned int *num_planes,
> > +             unsigned int sizes[], struct device *alloc_devs[])
> > +{
> > +     struct amvdec_session *sess =3D vb2_get_drv_priv(q);
> > +     const struct amvdec_format *fmt_out =3D sess->fmt_out;
> > +     u32 output_size =3D amvdec_get_output_size(sess);
> > +     u32 buffers_total;
> > +
> > +     if (*num_planes) {
>=20
> If you are not supporting create_bufs, then you can drop this part.
> Without create_bufs you can assume that *num_planes =3D=3D 0 and
> q->num_buffers =3D=3D 0.
>=20
> You should add a comment here mentioning that create_bufs isn't
> supported by this driver and explain why it isn't supported.
>=20
> I understand it is due to gstreamer problems, but the explanation
> in your cover letter didn't say why it is a problem with this driver
> but not other drivers (apparently).

There is problems in GStreamer with this, but it was disabled because
the firmware does not really allow adding buffers at run-time. Worst,
we would often seen kernel crash when this was enabled.

No decoder before this one implements CREATE_BUFS from what I'm aware,
which explain why I never catched the GStreamer issues before.

Nicolas

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