/dev/ttyUSB0 sounds like generic USB serial driver like FTDI or Profilic. This can change to /dev/ttyUSB1 etc. next time you plug in the USB-cable (use udevd to create fixed symbolic link).
There seems to be kernel module …/kernel/drivers/usb/serial/garmin_gps.ko too in my Raspberry Pi. Maybe unload other serial drivers if this is needed?
What do your get with lsusb? dmesg is also useful when USB is plugged in.
Longer command to list more properties for udev.
udevadm info --attribute-walk --path=/sys/bus/usb-serial/devices/ttyUSB0
or in older systems
udevinfo -a -p find /sys -name dev | grep ttyUSB0
73, Jaakko ac1bb/oh7bf