linux-arkmicro/linux/Documentation/devicetree/bindings/usb/usb-device.txt

Generic USB Device Properties

Usually, we only use device tree for hard wired USB device.
The reference binding doc is from:
http://www.devicetree.org/open-firmware/bindings/usb/usb-1_0.ps

Four types of device-tree nodes are defined: "host-controller nodes"
representing USB host controllers, "device nodes" representing USB devices,
"interface nodes" representing USB interfaces and "combined nodes"
representing simple USB devices.

A combined node shall be used instead of a device node and an interface node
for devices of class 0 or 9 (hub) with a single configuration and a single
interface.

A "hub node" is a combined node or an interface node that represents a USB
hub.


Required properties for device nodes:
- 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 number of the USB hub port or the USB host-controller port to which
  this device is attached. The range is 1-255.


Required properties for device nodes with interface nodes:
- #address-cells: shall be 2
- #size-cells: shall be 0


Required properties for interface nodes:
- compatible: "usbifVID,PID.configCN.IN", where VID is the vendor id, PID is
  the product id, CN is the configuration value and IN is the interface
  number. The textual representation of VID, PID, CN and IN 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
  "usbifVID,PID.configCN.IN".
- reg: the interface number and configuration value

The configuration component is not included in the textual representation of
an interface-node unit address for configuration 1.


Required properties for combined nodes:
- 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 number of the USB hub port or the USB host-controller port to which
  this device is attached. The range is 1-255.


Required properties for hub nodes with device nodes:
- #address-cells: shall be 1
- #size-cells: shall be 0


Required properties for host-controller nodes with device nodes:
- #address-cells: shall be 1
- #size-cells: shall be 0


Example:

&usb1 {	/* host controller */
	#address-cells = <1>;
	#size-cells = <0>;

	hub@1 {		/* hub connected to port 1 */
		compatible = "usb5e3,608";
		reg = <1>;
	};

	device@2 {	/* device connected to port 2 */
		compatible = "usb123,4567";
		reg = <2>;
	};

	device@3 { 	/* device connected to port 3 */
		compatible = "usb123,abcd";
		reg = <3>;

		#address-cells = <2>;
		#size-cells = <0>;

		interface@0 {	/* interface 0 of configuration 1 */
			compatible = "usbif123,abcd.config1.0";
			reg = <0 1>;
		};

		interface@0,2 {	/* interface 0 of configuration 2 */
			compatible = "usbif123,abcd.config2.0";
			reg = <0 2>;
		};
	};
};