ME910G1 Integration

[Jack Broderick]

Hello,

I've been working on integrating the Telit ME910G1 into our platform and
have found some interesting behavior that I wanted to share and ask for
some feedback:

*USB Composition*
The USB composition
<https://y1cj3stn5fbwhv73k0ipk1eg-wpengine.netdna-ssl.com/wp-content/uploads/2021/06/Telit_Modules_Linux_USB_Drivers_User_Guide_r10.pdf>
for the device is:

      0x110a: 3 reduced ACM devices. The composition also 1 rmnet adapter,
but it can’t be used for data calls, just for controlling the device

The kernel I am running does not have support for the qmi_wwan driver for
this ID, so by default I only got the ttyUSBX devices. As a result,
ModemManager defaulted to using PPP for setting up the connection. This
worked perfectly fine. I haven't used PPP much since our other modems
support qmi. We are using OpenWRT and I did find that the pppd setup
scripts create a default route with no metric when the interface comes up.
Since the ModemManager Luci page supports metrics, I wanted to have this
functionality. I created a custom ppp-up script to get called by pppd that
gets the metric via uci get and adds that via json_add_int. It's not the
cleanest approach, so I would be curious if anyone else has faced an issue
like this?

I then wanted to have the cdc-wdm interface available for getting signal
info while the interface is up. Adding support in runtime with:

 echo "1bc7 110a" > /sys/bus/usb/drivers/qmi_wwan/new_id

worked, and I was able to use qmicli to query the modem. The issue is,
however, that ModemManager then wanted to use the qmi interface for setting
up the interface. I think I would like to force ModemManager to use PPP in
this specific instance (maybe I can change the primary port to ttyUSB?). I
haven't experienced a modem with this "partial" rmnet adapter, I'm assuming
it's not very common, so I'm not exactly sure what an ideal ModemManager
behavior would be but it seems like an interesting problem to solve.

Cheers,
Jack
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