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From:   Jernej =?utf-8?B?xaBrcmFiZWM=?= <jernej.skrabec@gmail.com>
To:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Samuel Holland <samuel@sholland.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Chen-Yu Tsai <wenst@chromium.org>
Cc:     Chen-Yu Tsai <wenst@chromium.org>, linux-media@vger.kernel.org,
        linux-sunxi@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org,
        Nicolas Dufresne <nicolas.dufresne@collabora.com>
Subject: Re: [PATCH] media: cedrus: Convert to MPLANE uAPI
Date:   Mon, 05 Dec 2022 22:01:14 +0100
Message-ID: <45143854.fMDQidcC6G@kista>
In-Reply-To: <20221129074530.640251-1-wenst@chromium.org>
References: <20221129074530.640251-1-wenst@chromium.org>
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Hi Chen-Yu!

Dne torek, 29. november 2022 ob 08:45:30 CET je Chen-Yu Tsai napisal(a):
> The majority of the V4L2 stateless video decoder drivers use the MPLANE
> interface.
> 
> On the userspace side, Gstreamer supports non-MPLANE and MPLANE
> interfaces. Chromium only supports the MPLANE interface, and is not yet
> usable with standard desktop Linux. FFmpeg support for either has not
> landed.

I don't like fixing userspace issues in kernel, if kernel side works fine. 
Implementing missing non-MPLANE support in Chromium will also allow it to work 
with older kernels.

Hans, what's linux-media politics about such changes?

Best regards,
Jernej

> 
> A fallback route using libv4l is also available. The library translates
> MPLANE interface ioctl calls to non-MPLANE ones, provided that the pixel
> format used is single plane.
> 
> Convert the Cedrus driver to the MPLANE interface, while keeping the
> supported formats single plane. Besides backward compatibility through
> the plugin, the hardware requires that different planes not be located
> too far apart in memory. Keeping the single plane pixel format makes
> this easy to enforce.
> 
> Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
> ---
> 
> This has been tested with Fluster. The score remained the same with or
> without the patch. This also helps with getting VP8 decoding working
> with Chromium's in-tree test program "video_decode_accelerator_tests",
> though Chromium requires other changes regarding buffer allocation and
> management.