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

[Shengjiu Wang]

Hi Mark

On Tue, Jul 4, 2023 at 12:03 PM Shengjiu Wang <shengjiu.wang at gmail.com>
wrote:

>
>
> On Tue, Jul 4, 2023 at 1:59 AM Mark Brown <broonie at 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?

best regards
wang shengjiu

>
>
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