[pulseaudio-discuss] UCM and modem PCMs (again)

[Arun Raghavan]

Hi folks,
So we're at the point where we are (at least I am :p) being bitten by
having to deal with always-open modem PCMs again.

The tl;dr summary of the situation is: we're dealing with phones where
you have to hold an ALSA device open to enable routing from the
baseband chip to the CODEC, even if the CPU isn't involved in the
process at all.

At the end of the last discussion, Mark/Pierre suggested it makes more
sense to deal with this in the kernel, which makes sense. However,
about a year later, Android kernels don't seem to be going down this
route. From what I can tell, it's not exactly trivial to modify the
drivers to work this way, so the pragmatic approach for now seems to be
to deal with this in userspace rather than have to bash at every
Android kernel on which we're trying to enable PulseAudio.

The first patch in this set is the same as the one I posted last year.
The second actually goes ahead and implements logic to allow UCM config
to signal such devices and the PA-side code to set up the devices
appropriately.

Cheers,
Arun