ModemManager can't open serial port after previously opening it successfully

[Aleksander Morgado]

> I did some further testing and while ModemManager is continually reporting the serial port can't be opened, I was able to connect to the port and send AT commands to the modem and the modem responded.  This means there is something in ModemManager that is triggering these messages and not the modem itself
>
> I have also been able to regularly reproduce this issue with ModemManager 1.8.0 by just connecting a data connection, disconnecting my antennas for about 5-10 minutes (simulates loss of signal in a poor signal area), and reconnecting the antennas (simulates moving into a good signal area).  ModemManager never recovers until the ModemManager process is restarted.
>
> I see that ModemManager is reporting "(ttyACM0) unexpected port hangup!" and then "(ttyACM0) forced to close port".  After that ModemManager is unable to connect again to ttyACM0.  It looks like the issue may be in the serial port force close code or whatever caused the force close to occur.
>

This look like a modem crash actually. When this previous issue
happens, do you see the ttyACM0 port going away from the system? (e.g.
in dmesg output)


-- 
Aleksander
https://aleksander.es