Hi,

I connected a USB bus between an iMX6ULZ and an 4G LTE modem, it was
running well in kernel 4.19.75. I've just upgraded kernel to 5.10.59,
the USB is broken, the USB drivers were disconnected / connected
repeatedly:

[12781.730889] usb 1-1: USB disconnect, device number 84
[12781.808317] option1 ttyUSB0: GSM modem (1-port) converter now
disconnected from ttyUSB0
[12781.839256] option 1-1:1.0: device disconnected
[12781.959687] option1 ttyUSB1: GSM modem (1-port) converter now
disconnected from ttyUSB1
[12782.009476] option 1-1:1.2: device disconnected
[12785.607012] usb 1-1: new high-speed USB device number 85 using ci_hdrc
[12785.825218] usb 1-1: New USB device found, idVendor=05c6,
idProduct=90b2, bcdDevice= 0.00
[12785.833828] usb 1-1: New USB device strings: Mfr=3, Product=2, SerialNumber=4
[12785.841222] usb 1-1: Product: Qualcomm CDMA Technologies MSM
[12785.847049] usb 1-1: Manufacturer: Qualcomm, Incorporated
[12785.852536] usb 1-1: SerialNumber: 674a1bcf
[12785.932542] option 1-1:1.0: GSM modem (1-port) converter detected
[12785.957103] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB0
[12785.975924] option 1-1:1.2: GSM modem (1-port) converter detected
[12786.047708] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB1

What could I be missing in kernel 5?

Thank you.

Kind regards,

- JH