Register LTE USB modem device on specific interface on boot

Installing and Using OpenWrt
1

So I have a RUT955 with OpenWRT, it has one built in LTE modem with 2 sim slots. I am currently connecting a second USB device with a LTE modem and a simcard to use as failover with MWAN3.

I have two interfaces:
LTE_builtin (/dev/cdc-wdm0)
LTE_USB (/dev/cdc-wdm1)

If boot first and then plug in the USB modem I get like I want but when I boot with them both plugged in LTE_builtin becomes the USB and the LTE_USB is the built in modem which screws my configuration.

How can I register the device to the right interface on boot?

I'd like
/dev/cdc-wdm0 to be LTE_builtin
/dev/cdc-wdm1 to be LTE_USB


root@iron:~# lsusb -v 
Bus 001 Device 004: ID 2c7c:0125 Quectel EG25-GC
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass          239
  bDeviceSubClass         2
  bDeviceProtocol         1
  bMaxPacketSize0        64
  idVendor           0x2c7c
  idProduct          0x0125
  bcdDevice            3.18
  iManufacturer           1 Quectel
  iProduct                2 EG25-GC
...
Bus 001 Device 005: ID 2c7c:0125 Android Android
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass          239
  bDeviceSubClass         2
  bDeviceProtocol         1
  bMaxPacketSize0        64
  idVendor           0x2c7c
  idProduct          0x0125
  bcdDevice            3.18
  iManufacturer           1 Android
  iProduct                2 Android


root@iron:~# dmesg
--USB MODEM--
[   17.390569] qmi_wwan 1-1.1:1.4: cdc-wdm0: USB WDM device
[   17.407330] qmi_wwan 1-1.1:1.4 wwan0: register 'qmi_wwan' at usb-1b000000.usb-1.1, WWAN/QMI device, 16:e9:bc:a1:c9:5c
[   17.418410] usbcore: registered new interface driver qmi_wwan
[   17.689859] usbcore: registered new interface driver option
[   17.695708] usbserial: USB Serial support registered for GSM modem (1-port)
[   17.703698] option 1-1.1:1.0: GSM modem (1-port) converter detected
[   17.710469] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB0
[   17.718010] option 1-1.1:1.1: GSM modem (1-port) converter detected
[   17.724767] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB1
[   17.732327] option 1-1.1:1.2: GSM modem (1-port) converter detected
[   17.739081] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB2
[   17.746649] option 1-1.1:1.3: GSM modem (1-port) converter detected
[   17.753410] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB3

--THIS IS THE INTERNAL MODEM--
[   52.671178] option 1-1.4:1.0: GSM modem (1-port) converter detected
[   52.678063] usb 1-1.4: GSM modem (1-port) converter now attached to ttyUSB4
[   52.686111] option 1-1.4:1.1: GSM modem (1-port) converter detected
[   52.692936] usb 1-1.4: GSM modem (1-port) converter now attached to ttyUSB5
[   52.700967] option 1-1.4:1.2: GSM modem (1-port) converter detected
[   52.707776] usb 1-1.4: GSM modem (1-port) converter now attached to ttyUSB6
[   52.715836] option 1-1.4:1.3: GSM modem (1-port) converter detected
[   52.722622] usb 1-1.4: GSM modem (1-port) converter now attached to ttyUSB7
[   53.238726] qmi_wwan 1-1.4:1.4: cdc-wdm1: USB WDM device
[   53.299500] qmi_wwan 1-1.4:1.4 wwan1: register 'qmi_wwan' at usb-1b000000.usb-1.4, WWAN/QMI device, 16:e9:bc:a1:c9:5c
2

Load the required modules for the USB modem after the built in modem comes up, then it should always be the 2nd interface ?

.... or do they require exactly the same modules ?

Here's another option, I guess [How-To] disable unused USB ports to reduce router power consumption

3rd option is to identify which modem's which, then create softlinks, for both cdc-wdm0/1, and use those instead of the real ones.

It might also be possible to rename the cdc-wdm0/1 so it uses unique names from start Reorder phy name after update

3

Thanks for the suggestions, the disable part you suggested did not work as well no the hardware.

I am unsure how to check which modules are used for the usb and builtin modem. How would I go about to check and also disable these modules?

Thanks!

4

remove the USB modem, reboot, and run lsmod.

reinsert the USB modem, see if lsmod changed.

5

Sadly the internal- and usb-modem seem to use the same modules.

6

I'm trying to understand hotplug https://openwrt.org/docs/guide-user/base-system/hotplug#coldplug

Could this be something to work with?