/sys/class/tty/ttyS0/device/bus/devices/rt3xxx-ehci/usb2/2-0%3A1.0/usb_endpoint%3Ausbdev2.1_ep81/subsystem/

../
usbdev1.1_ep00/
usbdev1.1_ep81/
usbdev2.1_ep00/
usbdev2.1_ep81/