Re: [PATCH 1/6] media: v4l2: Add audio capture and output support

[Shengjiu Wang <shengjiu.wang@gmail.com>]

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Hi Mark

On Fri, Jul 7, 2023 at 11:13 AM Shengjiu Wang <shengjiu.wang@gmail.com>
wrote:

> Hi Mark
>
> On Tue, Jul 4, 2023 at 12:03 PM Shengjiu Wang <shengjiu.wang@gmail.com>
> wrote:
>
>>
>>
>> On Tue, Jul 4, 2023 at 1:59 AM Mark Brown <broonie@kernel.org> wrote:
>>
>>> On Mon, Jul 03, 2023 at 03:12:55PM +0200, Hans Verkuil wrote:
>>>
>>> > My main concern is that these cross-subsystem drivers are a pain to
>>> > maintain. So there have to be good reasons to do this.
>>>
>>> > Also it is kind of weird to have to use the V4L2 API in userspace to
>>> > deal with a specific audio conversion. Quite unexpected.
>>>
>>> > But in the end, that's a decision I can't make.
>>>
>>> > So I wait for that feedback. Note that if the decision is made that
>>> this
>>> > can use V4L2, then there is quite a lot more that needs to be done:
>>> > documentation, new compliance tests, etc. It's adding a new API, and
>>> that
>>> > comes with additional work...
>>>
>>> Absolutely, I agree with all of this - my impression was that the target
>>> here would be bypass of audio streams to/from a v4l2 device, without
>>> bouncing through an application layer.  If it's purely for audio usage
>>> with no other tie to v4l2 then involving v4l2 does just seem like
>>> complication.
>>>
>>
>> This audio use case is using the v4l2 application layer. in the user space
>> I need to call below v4l2 ioctls to implement the feature:
>> VIDIOC_QUERYCAP
>> VIDIOC_TRY_FMT
>> VIDIOC_S_FMT
>> VIDIOC_REQBUFS
>> VIDIOC_QUERYBUF
>> VIDIOC_STREAMON
>> VIDIOC_QBUF
>> VIDIOC_DQBUF
>> VIDIOC_STREAMOFF
>>
>> why the driver was put in the ALSA, because previously we implemented
>> the ASRC M2P (memory to peripheral) in ALSA,  so I think it is better to
>> add M2M driver in ALSA.  The hardware IP is the same. The compatible
>> string is the same.
>>
>>
>> Could you please share more of your ideas about this patch? and could
> you please check further about this implementation.
>
> I tried to find a good interface in ALSA for this m2m request, but didn't
> find one,  then I try the V4L2, find it is good this audio case.
>
> but it needs to extend the V4L2 API.
>
> I have no idea how to go on, could you please recommend?
>
>
Should I implement the asrc m2m driver as a separate v4l2 driver?
And move it to the /driver/media folder ? In ALSA part, just need
register the platform device.

The bridge between ALSA and V4L2 framework can be the header
file in /include/sound/

Does it sound better?

Best regards
Wang Shengjiu

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