I am using the M.2 connector on the Radxa Rock 5B+ board to connect an LTE module (EM7455). According to the datasheet and engineers, this M.2 slot is connected to the board via a USB hub (USB 2.0).
When using the official Radxa OS, I can successfully detect the module under lsusb, the necessary kernel modules load correctly, ModemManager recognizes the modem, and I can establish an internet connection.
However, on Armbian, I am experiencing a strange issue. The device does not consistently appear under lsusb; instead, the logs show that it keeps connecting and disconnecting in an endless loop. I am unsure of the root cause and how I can gather more detailed logs.
Since I am dual-booting with the official Radxa OS (Debian) and the modem works fine there, I believe this is not a hardware issue. Below are the relevant dmesg logs for further analysis.(dmesg)
[ 115.811271] qcserial 4-1.4:1.0: Qualcomm USB modem converter detected
[ 115.8Preformatted text12190] usb 4-1.4: Qualcomm USB modem converter now attached to ttyUSB0
[ 116.882327] usb 4-1.4: USB disconnect, device number 9
[ 116.883136] qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
[ 116.883201] qcserial 4-1.4:1.0: device disconnected
[ 130.325805] usb 4-1.4: new high-speed USB device number 10 using ehci-platform
[ 130.524496] usb 4-1.4: New USB device found, idVendor=1199, idProduct=9070, bcdDevice= 0.00
[ 130.524554] usb 4-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 130.524584] usb 4-1.4: Product: Sierra Wireless EM7455 Qualcomm
[ 130.524610] usb 4-1.4: Manufacturer: Sierra Wireless, Incorporated
[ 130.524636] usb 4-1.4: SerialNumber: LF{XXX}
[ 130.527209] qcserial 4-1.4:1.0: Qualcomm USB modem converter detected
[ 130.528144] usb 4-1.4: Qualcomm USB modem converter now attached to ttyUSB0
[ 131.602614] usb 4-1.4: USB disconnect, device number 10
[ 131.603279] qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
[ 131.603339] qcserial 4-1.4:1.0: device disconnected
[ 145.045108] usb 4-1.4: new high-speed USB device number 11 using ehci-platform
[ 145.243503] usb 4-1.4: New USB device found, idVendor=1199, idProduct=9070, bcdDevice= 0.00
[ 145.243521] usb 4-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 145.243528] usb 4-1.4: Product: Sierra Wireless EM7455 Qualcomm
[ 145.243535] usb 4-1.4: Manufacturer: Sierra Wireless, Incorporated
[ 145.243540] usb 4-1.4: SerialNumber: LF{XXX}
[ 145.244431] qcserial 4-1.4:1.0: Qualcomm USB modem converter detected
[ 145.244712] usb 4-1.4: Qualcomm USB modem converter now attached to ttyUSB0
[ 146.322437] usb 4-1.4: USB disconnect, device number 11
[ 146.323113] qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
[ 146.323183] qcserial 4-1.4:1.0: device disconnected
[ 159.751520] usb 4-1.4: new high-speed USB device number 12 using ehci-platform
[ 159.949674] usb 4-1.4: New USB device found, idVendor=1199, idProduct=9070, bcdDevice= 0.00
[ 159.949698] usb 4-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 159.949705] usb 4-1.4: Product: Sierra Wireless EM7455 Qualcomm
[ 159.949711] usb 4-1.4: Manufacturer: Sierra Wireless, Incorporated
[ 159.949717] usb 4-1.4: SerialNumber: LF{XXX}
[ 159.950592] qcserial 4-1.4:1.0: Qualcomm USB modem converter detected
[ 159.950877] usb 4-1.4: Qualcomm USB modem converter now attached to ttyUSB0
[ 161.028727] usb 4-1.4: USB disconnect, device number 12
[ 161.029336] qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
[ 161.029399] qcserial 4-1.4:1.0: device disconnected
I tried blocking the `qcserial` driver, but it keeps connecting and disconnecting in a nonstop loop again.
Not sure if it could be any power configuration problem “echo ‘-1’ | sudo tee /sys/module/usbcore/parameters/autosuspend” didn't help me.
MoreDetaildLogs: https://paste.next.armbian.com/iwiqanihuw
LTE Module: Sierra Wireless EM7455 Qualcomm
Linux rock-5b-plus 6.1.99-vendor-rk35xx
Distributor ID: Ubuntu
Description: Armbian 25.2.2 noble
Release: 24.04
Codename: noble
