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

Hi Mark

On Tue, Jul 4, 2023 at 12:03 PM Shengjiu Wang [off-list ref]
wrote:

On Tue, Jul 4, 2023 at 1:59 AM Mark Brown [off-list ref] wrote:

quoted

On Mon, Jul 03, 2023 at 03:12:55PM +0200, Hans Verkuil wrote:

quoted

My main concern is that these cross-subsystem drivers are a pain to
maintain. So there have to be good reasons to do this.

quoted

Also it is kind of weird to have to use the V4L2 API in userspace to
deal with a specific audio conversion. Quite unexpected.

quoted

But in the end, that's a decision I can't make.

quoted

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

quoted

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