Most older Qualcomm SoCs (e.g. MSM8916, MSM8974, ...) communicate
with the modem through shared memory. On mainline kernels these
shared memory channels are exposed through the RPMSG subsystem.
This is different from communication through USB or serial interfaces
that are currently supported by ModemManager.
This commit forks the "modemmanager" package from Alpine and adds
a patch that allows ModemManager to talk to modems through the RPMSG
subsystem.
Working functionality: Calls, SMS, Mobile Data
The same patch has also been submitted upstream:
https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/363
