linux-kernel - Re: [PATCH 10/10] venus: dec: make decoder compliant with stateful codec API

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Message-ID: <01b6683f-9378-e6f2-501f-e2213e6c690d@xs4all.nl>
Date:   Tue, 21 May 2019 14:27:27 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Tomasz Figa <tfiga@...omium.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Vikash Garodia <vgarodia@...eaurora.org>,
        Alexandre Courbot <acourbot@...omium.org>,
        Malathi Gottam <mgottam@...eaurora.org>
Subject: Re: [PATCH 10/10] venus: dec: make decoder compliant with stateful
 codec API

On 5/21/19 11:09 AM, Tomasz Figa wrote:
> Hi Stan,
> 
> On Mon, May 20, 2019 at 11:47 PM Stanimir Varbanov
> <stanimir.varbanov@...aro.org> wrote:
>>
>> Hi Tomasz,
>>
>> On 4/24/19 3:39 PM, Tomasz Figa wrote:
>>> On Wed, Apr 24, 2019 at 9:15 PM Stanimir Varbanov
>>> <stanimir.varbanov@...aro.org> wrote:
>>>>
>>>> Hi Hans,
>>>>
>>>> On 2/15/19 3:44 PM, Hans Verkuil wrote:
>>>>> Hi Stanimir,
>>>>>
>>>>> I never paid much attention to this patch series since others were busy
>>>>> discussing it and I had a lot of other things on my plate, but then I heard
>>>>> that this patch made G_FMT blocking.
>>>>
>>>> OK, another option could be to block REQBUF(CAPTURE) until event from hw
>>>> is received that the stream is parsed and the resolution is correctly
>>>> set by application. Just to note that I'd think to this like a temporal
>>>> solution until gstreamer implements v4l events.
>>>>
>>>> Is that looks good to you?
>>>
>>> Hmm, I thought we concluded that gstreamer sets the width and height
>>> in OUTPUT queue before querying the CAPTURE queue and so making the
>>> driver calculate the CAPTURE format based on what's set on OUTPUT
>>> would work fine. Did I miss something?
>>
>> Nobody is miss something.
>>
>> First some background about how Venus implements stateful codec API.
>>
>> The Venus firmware can generate two events "sufficient" and
>> "insufficient" buffer requirements (this includes decoder output buffer
>> size and internal/scratch buffer sizes). Presently I always set minimum
>> possible decoder resolution no matter what the user said, and by that
>> way I'm sure that "insufficient" event will always be triggered by the
>> firmware (the other reason to take this path is because this is the
>> least-common-divider for all supported Venus hw/fw versions thus common
>> code in the driver). The reconfiguration (during codec Initialization
>> sequence) is made from STREAMON(CAPTURE) context. Now, to make that
>> re-configuration happen I need to wait for "insufficient" event from
>> firmware in order to know the real coded resolution.
>>
>> In the case of gstreamer where v4l2_events support is missing I have to
>> block (wait for firmware event) REQBUF(CAPTURE) (vb2::queue_setup) or
>> STREAMON(CAPTURE) (vb2::start_streaming).
>>
>> I tried to set the coded resolution to the firmware as-is it set by
>> gstreamer but then I cannot receive the "sufficient" event for VP8 and
>> VP9 codecs. So I return back to the solution with minimum resolution above.
>>
>> I'm open for suggestions.
> 
> I think you could still keep setting the minimum size and wait for the
> "insufficient" event. At the same time, you could speculatively
> advertise the expected "sufficient" size on the CAPTURE queue before
> the hardware signals those. Even if you mispredict them, you'll get
> the event, update the CAPTURE resolution and send the source change
> event to the application, which would then give you the correct
> buffers. Would that work for you?

As I understand it this still would require event support, which gstreamer
doesn't have.

I think it is OK to have REQBUFS sleep in this case. However, I would only
enable this behavior if the application didn't subscribe to the SOURCE_CHANGE
event. That's easy enough to check in the driver. And that means that if the
application is well written, then the driver will behave in a completely
standard way that the compliance test can check.

Regards,

	Hans