USB errors with qmi-wwan

[Geert Lens]

Hi,

We are using the QMI interface on the Quectel BG96 modem and everything
works fine, but after a few hours the connection is suddenly disconnected
and the qmi_proxy starts hogging CPU.

During this time the USB interfaces of the modem are not responding and
will only work again after the modem is physically turned off and on.

Output from dmesg:

*qmi_wwan 1-1:1.4: nonzero urb status received: -71*
*qmi_wwan 1-1:1.4: wdm_int_callback - 0 bytes*
*qmi_wwan 1-1:1.4: nonzero urb status received: -71*
*qmi_wwan 1-1:1.4: wdm_int_callback - 0 bytes*
*qmi_wwan 1-1:1.4: nonzero urb status received: -71*
*qmi_wwan 1-1:1.4: wdm_int_callback - 0 bytes*
*qmi_wwan 1-1:1.4: nonzero urb status received: -71*
*qmi_wwan 1-1:1.4: wdm_int_callback - 0 bytes*

I have read that the -71 (EPROTO) is mostly caused by hardware or firmware
issues and that it can cause the kernel to disable the device, is
this correct? Or could it be something else?

Version used:
- Linux kernel: v4.14.78
- ModemManager: v1.12.10
- libqmi: v1.24.10

*Geert*
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