So far we have only created /dev/modem based on the DATA5_CNTL
channel available from the modem. The DATAX_CNTL channels allow
sending QMI messages to the modem. This is sufficient for oFono
to work.
Unfortunately, ModemManager currently does not support starting
calls through the QMI interface. Instead, it uses serial AT commands
that can be alternatively used on all USB-based Qualcomm modems.
It turns out that we can also send serial AT commands through
the RPMSG interface: the DATAX channels (without _CNTL) all respond
to serial AT commands. We set it up at /dev/modem-at, configure
ModemManager accordingly and then we are able to start calls. Yay!
Newer Qualcomm SoCs (e.g. SDM845. MSM8953) seem to use a different
method to talk to the modem. There are no longer separate rpmsg/SMD
channels for QMI messags, instead the modem is also available through QRTR.
On these newer SoCs, installing msm-modem-mainline is pointless,
because the created /dev/modem device will not actually allow
communicating with the modem. However, you still need the part from
the base package (msm-modem), which installs+enables rmtfs.
To avoid confusion, rename the msm-modem-mainline subpackage to
msm-modem-rpmsg. Install only "msm-modem" on SDM845 because that
likely does not allow communication with the modem through RPMSG
anyway.
2020-06-25 09:41:35 +02:00
Renamed from modem/msm-modem/udev-mainline.rules (Browse further)
