Don’t know if this helps, but on the default kernel config of a TX1 R28.2:
# CONFIG_USB_SERIAL_CH341 is not set
…which implies the driver can probably be added as a module, but if your “/proc/config.gz” does not have this, then the ch341 driver is missing. In one form or another CH341 hardware will need this.
Looks like the ttyGS0 is for the “gadget” interface…basically an emulated serial UART:
Since R28.2 (I think) there seems to have been some effort to set up USB “gadgets” when in device mode. I don’t know the purpose behind this, but my assumption is that in some future release there might be a desire to get away from using wired ethernet and letting it all go over USB…with USB emulating everything needed (I’m just speculating).
For your device, if it is CH341, then you’ll have to have the kernel driver before the “/dev” file shows up.