What:		/sys/bus/mdio_bus/devices/.../phy_id
Date:		November 2012
KernelVersion:	3.8
Contact:	netdev@vger.kernel.org
Description:
		This attribute contains the 32-bit PHY Identifier as reported
		by the device during bus enumeration, encoded in hexadecimal.
		This ID is used to match the device with the appropriate
		driver.

What:		/sys/bus/mdio_bus/devices/.../phy_interface
Date:		February 2014
KernelVersion:	3.15
Contact:	netdev@vger.kernel.org
Description:
		This attribute contains the PHY interface as configured by the
		Ethernet driver during bus enumeration, encoded in string.
		This interface mode is used to configure the Ethernet MAC with the
		appropriate mode for its data lines to the PHY hardware.