[alsa-devel] Best representation for TDM devices

[Mark Brown]

On Thu, Jul 25, 2019 at 03:01:12PM +0200, Maxime Ripard wrote:

> Since I have two codecs, I have two links (described through
> simple-card) and thus two subdevices. However, the microphones
> connected are really separate streams, so ideally (I guess?) we should
> have 1 subdevice per microphone.

> An alternative would be that we capture the whole 4 channels and use
> dsnoop to demux them, but trying to use the device directly (using
> arecord -D hw:0) results in the ioctl to change the number of channels
> being rejected, I'm assuming because each codec only has 2 channels?

> So I'm a bit lost at this point about how I should go and expose
> this. I couldn't really find any similar setup either in the
> kernel. Any preferred way of doing this?

What is the actual hardware - what do the microphones physically look
like in the system, what functional role do they play?  My initial guess
would be to combine them into a single PCM for userspace, there's some
support for that but it's not surprising if that's broken somewhere
along the line as it's very infrequently tested.
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