So I googled, CP2104 is a Silicon Labs chipset, another good UART manufacturer. I just need to find a USB to RS232 cable with SiLabs chipset, I guess it will be supported with built in driver. However, there is almost no USB to RS232 adapter/cable with Silicon Labs chipset available on the web. There are lots of USB to UART ones with SiLabs chipset just like the one GL-Inet has.

So probably I still need to use FTDI cables.

FTDI drivers are here: (not sure if I need the VCP driver which is not available for ARM)

http://www.ftdichip.com/Drivers/D2XX.htm

I suppose I should use the one marked for Raspberry Pi, right? How do I install it? Sorry that I am not familiar with Linux. After I install it, would I also have /dev/ttyUSB0?

Finally, does the stock firmware support any other chipset? How about the Prolific chipset (cheaper and not as good as FTDI and SiLabs, but widely available)?

Thanks a lot.