Re: [RFC PATCH 1/5] media: videodev2: add V4L2_FMT_FLAG_DYN_RESOLUTION

From: Tomasz Figa <tfiga@chromium.org>
To: Maxime Jourdan <mjourdan@baylibre.com>
Cc: Hans Verkuil <hans.verkuil@cisco.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Linux Media Mailing List <linux-media@vger.kernel.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Stanimir Varbanov <stanimir.varbanov@linaro.org>,
	Tiffany Lin <tiffany.lin@mediatek.com>,
	Andrew-CT Chen <andrew-ct.chen@mediatek.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Kamil Debski <kamil@wypas.org>,
	Jeongtae Park <jtp.park@samsung.com>,
	Andrzej Hajda <a.hajda@samsung.com>
Subject: Re: [RFC PATCH 1/5] media: videodev2: add V4L2_FMT_FLAG_DYN_RESOLUTION
Date: Wed, 3 Jul 2019 18:24:14 +0900	[thread overview]
Message-ID: <CAAFQd5AcLfihfrhhvwDiKLHA4t9L9R1=BPUAQWJ3vSc61LGzgw@mail.gmail.com> (raw)
In-Reply-To: <CAMO6nayMpngjM0k5ZQ08WPDhE5z4gCCxjRGnAzUp7fbrJJd45w@mail.gmail.com>

On Wed, Jun 12, 2019 at 1:46 AM Maxime Jourdan <mjourdan@baylibre.com> wrote:
>
> Hi Tomasz,
> On Mon, Jun 10, 2019 at 5:48 AM Tomasz Figa <tfiga@chromium.org> wrote:
> >
> > Hi Maxime,
> >
> > On Sun, Jun 9, 2019 at 11:38 PM Maxime Jourdan <mjourdan@baylibre.com> wrote:
> > >
> > > Add a enum_fmt format flag to specifically tag coded formats where
> > > dynamic resolution switching is supported by the device.
> > >
> > > This is useful for some codec drivers that can't support dynamic
> > > resolution switching for all their listed coded formats. It allows
> > > userspace to know whether it should extract the video parameters itself,
> > > or if it can rely on the device to send V4L2_EVENT_SOURCE_CHANGE when
> > > such changes are detected.
> > >
> >
> > First of all, thanks for the patch!
> >
> > Given the aspect of compatibility and also the general preference for
> > the drivers to actually handle dynamic resolution changes, I'd suggest
> > inverting the meaning of this flag. With something like
> > "V4L2_FMT_FLAG_STATIC_RESOLUTION" it would be more of an exception
> > rather than the default behavior.
> >
>
> This is actually what I did to begin with [0], with the same
> reasoning: not supporting dynamic resolution for a certain coded
> format is more of an exception than the norm (for decoders).
> The patch was ultimately dropped from the meson vdec series after
> discussing with Hans, see [0] or the lkml link Hans provided in his
> answer.
>
> We have the chance today that stateful decoders in the kernel either
> support V4L2_EVENT_SOURCE_CHANGE and dynamic resolution switching for
> all their formats, or they don't expose V4L2_EVENT_SOURCE_CHANGE at
> all.
> While this flag would change the spec, it wouldn't break existing
> userspace using close-to-spec drivers like s5p-mfc or mtk-vcodec.

Fair enough. Feel free to add my Reviewed-by, after Hans's comments are fixed.

Best regards,
Tomasz

>
> Cheers,
> Maxime
>
> [0] https://patchwork.kernel.org/patch/10969829/
>
> > Best regards,
> > Tomasz