http://www.devicetree.org/open-firmware/bindings/usb/usb-1_0.ps
Required properties:
-- compatible: usbVID,PID. The textual representation of VID, PID shall
- be in lower case hexadecimal with leading zeroes suppressed. The
- other compatible strings from the above standard binding could also
- be used, but a device adhering to this binding may leave out all except
- for usbVID,PID.
+- compatible: "usbVID,PID", where VID is the vendor id and PID the product id.
+ The textual representation of VID and PID shall be in lower case hexadecimal
+ with leading zeroes suppressed. The other compatible strings from the above
+ standard binding could also be used, but a device adhering to this binding
+ may leave out all except for "usbVID,PID".
- reg: the port number which this device is connecting to, the range
is 1-255.