linux-kernel - Re: [PATCH v4 3/5] staging: Introduce NVIDIA Tegra video decoder driver

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Date:   Sun, 10 Dec 2017 21:56:35 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Hans Verkuil <hverkuil@...all.nl>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Stephen Warren <swarren@...dotorg.org>,
        Vladimir Zapolskiy <vz@...ia.com>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        linux-media@...r.kernel.org, linux-tegra@...r.kernel.org,
        devel@...verdev.osuosl.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Giulio Benetti <giulio.benetti@...ronovasrl.com>
Subject: Re: [PATCH v4 3/5] staging: Introduce NVIDIA Tegra video decoder
 driver

On 05.12.2017 16:03, Hans Verkuil wrote:
> On 12/05/17 13:17, Dmitry Osipenko wrote:
>> Hi Hans,
>>
>> On 04.12.2017 17:04, Hans Verkuil wrote:
>>> Hi Dmitry,
>>>
>>> As you already mention in the TODO, this should become a v4l2 codec driver.
>>>
>>> Good existing examples are the coda, qcom/venus and mtk-vcodec drivers.
>>>
>>> One thing that is not clear from this code is if the tegra hardware is a
>>> stateful or stateless codec, i.e. does it keep track of the decoder state
>>> in the hardware, or does the application have to keep track of the state and
>>> provide the state information together with the video data?
>>>
>>> I ask because at the moment only stateful codecs are supported. Work is ongoing
>>> to support stateless codecs, but we don't support that for now.
>>>
>>
>> It is stateless. Is there anything ready to try out? If yes, could you please
>> give a reference to that work?
> 
> I rebased my two year old 'requests2' branch to the latest mainline version and
> gave it the imaginative name 'requests3':
> 
> https://git.linuxtv.org/hverkuil/media_tree.git/log/?h=requests3
> 
> (Note: only compile tested!)

Thank you very much.

> This is what ChromeOS has been using (actually they use a slightly older version)
> and the new version that is currently being developed will be similar, so any work
> you do on top of this will carry over to the final version without too much effort.
> 
> At least, that's the intention :-)
> 
> I've CC-ed Maxime and Giulio as well: they are looking into adding support for
> the stateless allwinner codec based on this code as well. There may well be
> opportunities for you to work together, esp. on the userspace side. Note that
> Rockchip has the same issue, they too have a stateless HW codec.

IIUC, we will have to define video decoder parameters in V4L API and then make a
V4L driver / userspace prototype (ffmpeg for example) that will use the requests
API for video decoding in order to upstream the requests API. Does it sound good?

>>
>>> Anyway, I'm OK with merging this in staging. Although I think it should go
>>> to staging/media since we want to keep track of it.
>>>
>>
>> Awesome, I'll move driver to staging/media in V5. Thanks!
> 
> Nice, thanks!