The board use Quectel EC200U 4G modem, use ECM mode, and use the latest OpenWrt master branch, compiled and burned to the board.
When initially booting, output register 'cdc_ether' at usb-1e1c0000.xhci-1, CDC Ethernet Device. I can see that there is a NIC for usb0.
[ 35.167751] mtk_soc_eth 1e100000.ethernet wan: PHY [mdio-bus:00] driver [MediaTek MT7530 PHY] (irq=POLL)
[ 35.177301] mtk_soc_eth 1e100000.ethernet wan: configuring for phy/rgmii-rxid link mode
[ 50.688074] usb 1-1: new high-speed USB device number 2 using xhci-mtk
[ 51.031457] usb 1-1: USB disconnect, device number 2
[ 57.338085] usb 1-1: new high-speed USB device number 3 using xhci-mtk
[ 57.518463] usb 1-1: config 1 has an invalid interface number: 6 but max is 5
[ 57.525585] usb 1-1: config 1 has no interface number 5
[ 57.538805] cdc_ether 1-1:1.0 usb0: register 'cdc_ether' at usb-1e1c0000.xhci-1, CDC Ethernet Device, ae:0c:29:a3:9b:6d
[ 57.551879] option 1-1:1.2: GSM modem (1-port) converter detected
[ 57.558719] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB0
[ 57.567433] option 1-1:1.3: GSM modem (1-port) converter detected
[ 57.574263] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB1
[ 57.582548] option 1-1:1.4: GSM modem (1-port) converter detected
[ 57.589335] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB2
[ 57.598360] option 1-1:1.6: GSM modem (1-port) converter detected
[ 57.605213] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB3
[ 83.600746] IPv6: ADDRCONF(NETDEV_CHANGE): usb0: link becomes ready
Then use the GPIO to power down the EC200U 4G modem, the system outputs unregister 'cdc_ether' usb-1e1c0000.xhci-1, CDC Ethernet Device, the usb0 NIC is disappeared, this is normal behavior:
[ 146.541628] usb 1-1: USB disconnect, device number 3
[ 146.546814] cdc_ether 1-1:1.0 usb0: unregister 'cdc_ether' usb-1e1c0000.xhci-1, CDC Ethernet Device
[ 146.690578] option1 ttyUSB0: GSM modem (1-port) converter now disconnected from ttyUSB0
[ 146.699270] option 1-1:1.2: device disconnected
[ 146.704901] option1 ttyUSB1: GSM modem (1-port) converter now disconnected from ttyUSB1
[ 146.713377] option 1-1:1.3: device disconnected
[ 146.718966] option1 ttyUSB2: GSM modem (1-port) converter now disconnected from ttyUSB2
[ 146.727378] option 1-1:1.4: device disconnected
[ 146.733039] option1 ttyUSB3: GSM modem (1-port) converter now disconnected from ttyUSB3
[ 146.741473] option 1-1:1.6: device disconnected
Next, the Quectel EC200U 4G modem was re-powered with GPIO, and the system output was missing the register 'cdc_ether' at usb-1e1c0000.xhci-1, CDC Ethernet Device., and I never saw the usb0 card again:
[ 159.530388] usb 1-1: new high-speed USB device number 4 using xhci-mtk
[ 159.877144] usb 1-1: USB disconnect, device number 4
[ 166.192167] usb 1-1: new high-speed USB device number 5 using xhci-mtk
[ 166.373377] usb 1-1: config 1 has an invalid interface number: 6 but max is 5
[ 166.380505] usb 1-1: config 1 has no interface number 5
[ 166.391840] option 1-1:1.0: GSM modem (1-port) converter detected
[ 166.400652] option 1-1:1.1: GSM modem (1-port) converter detected
[ 166.409970] option 1-1:1.2: GSM modem (1-port) converter detected
[ 166.417211] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB2
[ 166.425830] option 1-1:1.3: GSM modem (1-port) converter detected
[ 166.432768] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB3
[ 166.443708] option 1-1:1.4: GSM modem (1-port) converter detected
[ 166.451145] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB4
[ 166.460658] option 1-1:1.6: GSM modem (1-port) converter detected
[ 166.468511] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB5
This should be a bug in the cdc_ehter driver, how should I fix it?