Can't connect using ModemManager when modem is in QMI mode

[Aleksander Morgado]

Hey Jeff,

> I'm running a Sierra Wireless MC7455 modem with SWI9X30C_02.32.11.00 r8042 CARMD-EV-FRMWR2 firmware. Using ModemManager 1.18.2 on Ubuntu 20.04.
>
> I can get the modem to connect using mmcli -m 0 --simple-connect=. when the modem is in MBIM mode.
> I can get the modem to connect using qmicli and qmi-network when the modem is in QMI mode.
>
> But when I use mmcli with ModemManager, --simple-connect fails with
>
>     error: couldn't connect the modem: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Core.Cancelled: operation cancelled'
>

Oh, that is very strange.

> What is strange is that the modem seems to create a default bearer channel when it is enabled. Using simple-connect seems to create a second bearer channel which is rejected. But using -connect on the default bearer channel also fails.
>

The default bearer when enabled is the "initial EPS default bearer".
In ModemManager, this is an informative bearer object exclusively, you
cannot use it to trigger a connection. When simple connect creates the
new bearer, that's the one that should end up connected.

>
> Using simple connect results in two bearers.
>
> root at de-01:~# mmcli -m 1 --simple-connect='apn=broadband'
> error: couldn't connect the modem: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Core.Cancelled: operation cancelled'

This is what we need to understand. Could you gather MM daemon debug
logs while you attempt this simple-connect operation?
https://modemmanager.org/docs/modemmanager/debugging/

-- 
Aleksander
https://aleksander.es