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From:   Tomasz Figa <tfiga@chromium.org>
Date:   Mon, 27 Aug 2018 13:09:07 +0900
Message-ID: <CAAFQd5BSCGYS6_oPzv9xCsb3X-b3q5B3e4qe_Jbeeuixb0UT4g@mail.gmail.com>
Subject: Re: [PATCH 1/2] media: docs-rst: Document memory-to-memory video
 decoder interface
To:     Stanimir Varbanov <stanimir.varbanov@linaro.org>,
        Hans Verkuil <hverkuil@xs4all.nl>
Cc:     Linux Media Mailing List <linux-media@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        a.hajda@samsung.com, Kyungmin Park <kyungmin.park@samsung.com>,
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On Tue, Aug 21, 2018 at 8:29 PM Stanimir Varbanov
<stanimir.varbanov@linaro.org> wrote:
>
> Hi Tomasz,
>
> On 08/08/2018 05:55 AM, Tomasz Figa wrote:
> > On Tue, Aug 7, 2018 at 4:37 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>
> >>>>>>> +7.  If all the following conditions are met, the client may resume the
> >>>>>>> +    decoding instantly, by using :c:func:`VIDIOC_DECODER_CMD` with
> >>>>>>> +    ``V4L2_DEC_CMD_START`` command, as in case of resuming after the drain
> >>>>>>> +    sequence:
> >>>>>>> +
> >>>>>>> +    * ``sizeimage`` of new format is less than or equal to the size of
> >>>>>>> +      currently allocated buffers,
> >>>>>>> +
> >>>>>>> +    * the number of buffers currently allocated is greater than or equal to
> >>>>>>> +      the minimum number of buffers acquired in step 6.
> >>>>>>
> >>>>>> You might want to mention that if there are insufficient buffers, then
> >>>>>> VIDIOC_CREATE_BUFS can be used to add more buffers.
> >>>>>>
> >>>>>
> >>>>> This might be a bit tricky, since at least s5p-mfc and coda can only
> >>>>> work on a fixed buffer set and one would need to fully reinitialize
> >>>>> the decoding to add one more buffer, which would effectively be the
> >>>>> full resolution change sequence, as below, just with REQBUFS(0),
> >>>>> REQBUFS(N) replaced with CREATE_BUFS.
> >>>>
> >>>> What happens today in those drivers if you try to call CREATE_BUFS?
> >>>
> >>> s5p-mfc doesn't set the .vidioc_create_bufs pointer in its
> >>> v4l2_ioctl_ops, so I suppose that would be -ENOTTY?
> >>
> >> Correct for s5p-mfc.
> >
> > As Philipp clarified, coda supports adding buffers on the fly. I
> > briefly looked at venus and mtk-vcodec and they seem to use m2m
> > implementation of CREATE_BUFS. Not sure if anyone tested that, though.
> > So the only hardware I know for sure cannot support this is s5p-mfc.
>
> In Venus case CREATE_BUFS is tested with Gstreamer.

Stanimir: Alright. Thanks for confirmation.

Hans: Technically, we could still implement CREATE_BUFS for s5p-mfc,
but it would need to be restricted to situations where it's possible
to reinitialize the whole hardware buffer queue, i.e.
- before initial STREAMON(CAPTURE) after header parsing,
- after a resolution change and before following STREAMON(CAPTURE) or
DECODER_CMD_START (to ack resolution change without buffer
reallocation).

Would that work for your original suggestion?

Best regards,
Tomasz