Voice call support on EC25-E with Android RIL driver

Hello Support Team,

so far I have managed to get the EC25-E up and running with an older RIL 1.1 that was provided to me here in the forums. As far as I can tell everything is working as it should however I’m not getting any audio during voice calls.
The modem dials just fine and the call is started and established properly but I / the person on the other end cant hear anything. This applies to both using the default configuration of the modem (which as far as I know transfers audio over serial) and the UAC mode.

Due to my android setup being a bit weird I’m not sure whether this issue is caused by the driver not being configured properly or by my android itself.

The setup is as follows:
I have Debian Testing running on a Desktop computer (x86_64) and Android 13 running within Waydroid. Waydroid uses an LXC container under the hood to run everything that makes up the android operating system except for the Linux kernel. That is shared with the host system. By doing so it allows Android to access the hardware of the host (in this case the EC25-E connected through USB).
I have configured the LXC container to forward both the USB device under /dev/bus/usb as well as the relevant /dev/tty* devices and in case of UAC the /dev/snd/controlC and /dev/snd/pcmC*D*p devices.
The RIL driver is then able to auto detect the modem and configure it properly.
Cellular Data, Calling (without audio however!), running USSD codes and GPS are all working so i seems that I have forwarded everything it should need.
When using UAC mode I can even see the sound meter in the pavucontrol application on my linux host system show something when I start a call but there is no sound through the call app on android.

How would I go about getting calls with sound to work ?
Do I need to add some extra configuration for the RIL driver so it know the default audio input and output devices that android is using ?
Do I need to tell it which sound card the modem actually is (in case of UAC mode) ?
Or what can I do to debug where things are going wrong ?

Quectel RIL supports phone calls, SMS, data connection and more. For the voice call, the module must support PCM, RIL will only send Voice Call AT commands, such as ATD and ATA, ATH. None of this has anything to do with UAC. L UAC is supported on Linux. For details, see Quectel_LTE_Standard_UAC_Application_Note_V1.0.pdf. But how to use on Android, such as you want to play the sound for the remote, or record the sound from the remote, these involve Android Audio, Android to transplant the ALSA driver, select the audio path, adapt to Android HAL, this requires the Android side, That’s RK3568 for support. Android Audio is complex.
If any other manufacturer’s 4G module supports UAC to make and receive calls on Android, Quectel will also develop this feature.

I was already starting to suspect that that’s how it is supposed to work.
In that case I’ll probably have to write a system service for android that checks if a call is currently starting / ongoing / ending and changes the audio routing dynamically.

Yes. I do agree and the Quectel RD think also.
But actually till now I haven’t seen anyone make it success.