Modem instance reconnects automatically using EM7455

[Pradeep Gopanapalli]

Hello All,

We am seeing a strange issue where Modem instance reconnects automatically once
in a while, modem used in EM7455. This happens after some time of succesful
data connection and the once the issue occurs network is disrupted for 30-45 seconds.
This is very random and some times happens quite often like every 1 hour or so.
>From the debug logs I can see there is USB disconnect and qcdm reports "unexpected port hangup" .
I tried searching modemforums and issues in gitlab<https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/?search=forced%20to%20close%20port&sort=created_date&state=opened&first_page_size=20>, but didn't find any one reporting this kind
of behavior for EM7455, it would be of great help if anyone can throw some light on this failure.

Logs:
>From logs:
2023-02-03T16:56:13.564 INFO   kern   kernel:[16332.259560] usb 1-1.3: USB disconnect, device number 5
2023-02-03T16:56:13.044 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB0/qcdm] unexpected port hangup!
2023-02-03T16:56:13.044 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB0/qcdm] forced to close port
2023-02-03T16:56:13.044 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB0/qcdm] device open count is 0 (close)
2023-02-03T16:56:13.044 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB0/qcdm] closing serial port
2023-02-03T16:56:13.044 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB0/qcdm] serial port closed
2023-02-03T16:56:13.565 INFO   kern   kernel:[16332.261131] qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
2023-02-03T16:56:13.566 INFO   kern   kernel:[16332.261629] qcserial 1-1.3:1.0: device disconnected
2023-02-03T16:56:13.567 INFO   kern   kernel:[16332.262427] qcserial ttyUSB1: Qualcomm USB modem converter now disconnected from ttyUSB1
2023-02-03T16:56:13.567 INFO   kern   kernel:[16332.262472] qcserial 1-1.3:1.2: device disconnected
2023-02-03T16:56:13.047 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB2/at] unexpected port hangup!
2023-02-03T16:56:13.047 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB2/at] forced to close port
2023-02-03T16:56:13.047 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB2/at] device open count is 0 (close)
2023-02-03T16:56:13.047 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB2/at] closing serial port...
2023-02-03T16:56:13.047 DEBUG  daemon ModemManager[5106]: <debug> [modem0/ttyUSB2/at] serial port closed
2023-02-03T16:56:13.569 INFO   kern   kernel:[16332.264374] qcserial ttyUSB2: Qualcomm USB modem converter now disconnected from ttyUSB2
2023-02-03T16:56:13.569 INFO   kern   kernel:[16332.264424] qcserial 1-1.3:1.3: device disconnected                                  2023-02-03T16:56:13.572 INFO   kern   kernel:[16332.267600] qmi_wwan 1-1.3:1.8 wwan0: unregister 'qmi_wwan' usb-0000:00:16.0-1.3, WWAN/QMI device
2023-02-03T16:56:13.053 NOTICE daemon netifd: Network device 'wwan0' link is down


Versions used
libqmi: 1.28.6-1
libmbim: 1.24.8-1
modemmanager: 1.16.6.1
openwrt: 19.07 based solution.

Carrier : Vodafone
EM7455 firmware used: "SWI9X30C_02.24.03.00 r6978 CARMD-EV-FRMWR2 2017/03/02 13:36:45
response: '!IMPREF: ^M
 preferred fw version:    02.24.03.00^M
 preferred carrier name:  VODAFONE^M
 preferred config name:   VODAFONE_001.001_000^M
 current fw version:      02.24.03.00^M
 current carrier name:    VODAFONE^M
 current config name:     VODAFONE_001.001_000'

Thanks,
Pradeep G
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