Comment 5 for bug 1444717

I thought I'd take a look at the ModemManager logs while reproducing the bug.

ModemManager[3865]: <warn> (ttyUSB0): could not re-acquire serial port lock: (5) Input/output error

At this point I tried removing and inserting the device several times, monitoring dmesg inbetween, to see if the modeswitch happened. dmesg showed that it was mounting as a USB drive, but nothing more.

I then killed ModemManager, which restarted:

ModemManager[11409]: <info> ModemManager (version 1.0.0) starting...
ModemManager[11409]: <warn> Couldn't find support for device at '/sys/devices/pci0000:00/0000:00:19.0': not supported by any plugin
ModemManager[11409]: <warn> Couldn't find support for device at '/sys/devices/pci0000:00/0000:00:1c.2/0000:04:00.0': not supported by any plugin

I then removed and reinserted the device several times. dmesg again showed that it was mounting as a USB drive, and tellingly there were _no_ additional ModemManager logs during this time.

Eventually (perhaps on the sixth attempt?) the modeswitch happened and the modem became available. ModemManager logs at this point looked like:

ModemManager[11409]: <warn> (ttyUSB1): port attributes not fully set
ModemManager[11409]: <warn> (ttyUSB0): port attributes not fully set
(ModemManager:11409): GLib-CRITICAL **: Source ID 18 was not found when attempting to remove it
(ModemManager:11409): GLib-CRITICAL **: Source ID 20 was not found when attempting to remove it
ModemManager[11409]: <warn> (ttyUSB1): port attributes not fully set
(ModemManager:11409): GLib-CRITICAL **: Source ID 25 was not found when attempting to remove it
ModemManager[11409]: <info> Creating modem with plugin 'Huawei' and '2' ports
ModemManager[11409]: <warn> (ttyUSB1): port attributes not fully set
ModemManager[11409]: <info> Modem for device at '/sys/devices/pci0000:00/0000:00:14.0/usb1/1-3' successfully created
ModemManager[11409]: <warn> couldn't load Supported Modes: 'Couldn't retrieve supported modes'
ModemManager[11409]: <warn> couldn't load list of Own Numbers: 'Not found'
ModemManager[11409]: Invalid mobile equipment error code: 50
ModemManager[11409]: <info> Modem: state changed (unknown -> disabled)