linux-kernel - Re: [PATCHv4 1/2] media: docs-rst: Document memory-to-memory video decoder interface

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Message-ID: <02da6340-3174-c03b-ffad-cc9a0a58afab@xs4all.nl>
Date:   Wed, 10 Jul 2019 10:09:28 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexandre Courbot <acourbot@...omium.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Pawel Osciak <posciak@...omium.org>
Subject: Re: [PATCHv4 1/2] media: docs-rst: Document memory-to-memory video
 decoder interface

On 7/3/19 6:58 AM, Tomasz Figa wrote:
> Hi Hans,
> 
> On Mon, Jun 3, 2019 at 8:28 PM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
>>
>> From: Tomasz Figa <tfiga@...omium.org>
>>
>> Due to complexity of the video decoding process, the V4L2 drivers of
>> stateful decoder hardware require specific sequences of V4L2 API calls
>> to be followed. These include capability enumeration, initialization,
>> decoding, seek, pause, dynamic resolution change, drain and end of
>> stream.
>>
>> Specifics of the above have been discussed during Media Workshops at
>> LinuxCon Europe 2012 in Barcelona and then later Embedded Linux
>> Conference Europe 2014 in Düsseldorf. The de facto Codec API that
>> originated at those events was later implemented by the drivers we already
>> have merged in mainline, such as s5p-mfc or coda.
>>
>> The only thing missing was the real specification included as a part of
>> Linux Media documentation. Fix it now and document the decoder part of
>> the Codec API.
>>
>> Signed-off-by: Tomasz Figa <tfiga@...omium.org>
>> Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
>> ---
>>  Documentation/media/uapi/v4l/dev-decoder.rst  | 1084 +++++++++++++++++
>>  Documentation/media/uapi/v4l/dev-mem2mem.rst  |    8 +-
>>  Documentation/media/uapi/v4l/pixfmt-v4l2.rst  |    5 +
>>  Documentation/media/uapi/v4l/v4l2.rst         |   10 +-
>>  .../media/uapi/v4l/vidioc-decoder-cmd.rst     |   41 +-
>>  5 files changed, 1132 insertions(+), 16 deletions(-)
>>  create mode 100644 Documentation/media/uapi/v4l/dev-decoder.rst
>>
> 
> Thanks a lot for helping with remaining changes.
> 
> Just one thing inline our team member found recently.
> 
> [snip]
>> +Capture setup
>> +=============
>> +
> [snip]
>> +4.  **Optional.** Set the ``CAPTURE`` format via :c:func:`VIDIOC_S_FMT` on the
>> +    ``CAPTURE`` queue. The client may choose a different format than
>> +    selected/suggested by the decoder in :c:func:`VIDIOC_G_FMT`.
>> +
>> +    * **Required fields:**
>> +
>> +      ``type``
>> +          a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``.
>> +
>> +      ``pixelformat``
>> +          a raw pixel format.
> 
> The client should be able to set the width and height as well. It's a
> quite frequent case, especially in DMA-buf import mode, that the
> buffers are actually bigger (e.g. more alignment) than what we could
> get from the decoder by default. For sane hardware platforms it's
> reasonable to expect that such bigger buffers could be handled as
> well, as long as we update the width and height here.

I've added this:

     ``width``, ``height``
         frame buffer resolution of the decoded stream; typically unchanged from
         what was returned with :c:func:`VIDIOC_G_FMT`, but it may be different
         if the hardware supports composition and/or scaling.

Is that what you were looking for?

> 
> It's more like a clarification anyway, so if you think it would be
> better to just merge the current revision, I could send a follow up
> patch.
> 
> Regardless of that and FWIW:
> 
> Reviewed-by: Tomasz Figa <tfiga@...omium.org>

Thanks!

	Hans

> 
> Best regards,
> Tomasz
>