Missing RS232 Interface on RUT955 Routers with OpenWRT and ser2net

Hello

I'm facing an issue with a couple RUT955 routers running OpenWRT where the RS232 interface is not detected. While the RS485 interface (ttyATH1) is present as expected, the RS232 interface, typically seen as 'ttyACM0' on openwrt is missing. Im also using ser2net on these routers to manage serial port connections over network.

I've installed various USB serial drivers, but none of them have solved the problem.

Specifically i'm having an issue with devices based on the Cypress Semiconductor USB-UART LP chipset. The few i have with ftdi work fine after installing the driver.

I know its not broken because if i install teltonikas firmware, the RS232 and RS485 appear as normal and work.

Has anyone come across this issue before?
Help would be greatly appreciated!

So your actual issue is that your USB-UART converters are not detected due to missing drivers? Can you give us more details about the device, e.g. its USB device IDs?

That chip is probably kmod-usb-acm.

I would do a lsmod on the working and non-working RUT955s, both running Teltonikas stuff, and compare the outputs.
Also you need to check, whether working and non-working RUTs are both of the same hardware-variant
CONFIG_TARGET_ath79_generic_DEVICE_teltonika_rut955=y
CONFIG_TARGET_ath79_generic_DEVICE_teltonika_rut955-h7v3c0 is not set; _OLD_VARIANT