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

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Date:   Mon, 20 May 2019 17:47:44 +0300
From:   Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        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

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.

-- 
regards,
Stan