When I upgraded tinyalsa to the new 2.0.0 major release (with breaking
changes) I failed to test q6voiced properly, even though I explicitly
had to rebuild it against the new tinyalsa version (see MR 1941).
In tinyalsa 2.0.0, calling pcm_open() does not automatically call
pcm_prepare() anymore, which is responsible for actually starting any
audio streams. This means that the old version of q6voiced is almost
entirely broken - only by pure luck it's sometimes possible to get
voice call audio working if you play other audio simultaenously while
a voice call is active. This does not work for the microphone though.
The new q6voiced version now calls pcm_prepare() explicitly to fix this.
linux-postmarketos-qcom-msm8916 now supports voice call audio.
However, at the moment the audio stream needs to be explicitly started
by opening some PCM audio devices when the call is started
(even though no audio data is written to the PCM device).
Eventually this should go away by implementing codec2codec support
for q6voice in the kernel. In that case, the stream would be started
once the audio routes are set up using ALSA UCM. However, this is a bit
complicated actually so for now it's nice to have a workaround:
q6voiced listens on dbus for signals from oFono, and opens/closes the
PCM device when a call is initiated/ended in oFono. This essentially
makes voice call audio work out of the box (provided that the audio
routing, e.g. Earpiece and a microphone is set up appropriately).
Co-Authored-By: Nikita Travkin <nikitos.tr@gmail.com>
