What:		/sys/class/dual_role_usb/.../
Date:		June 2015
Contact:	Badhri Jagan Sridharan<badhri@google.com>
Description:
		Provide a generic interface to monitor and change
		the state of dual role usb ports. The name here
		refers to the name mentioned in the
		dual_role_phy_desc that is passed while registering
		the dual_role_phy_intstance through
		devm_dual_role_instance_register.

What:           /sys/class/dual_role_usb/.../supported_modes
Date:           June 2015
Contact:        Badhri Jagan Sridharan<badhri@google.com>
Description:
		This is a static node, once initialized this
		is not expected to change during runtime. "dfp"
		refers to "downstream facing port" i.e. port can
		only act as host. "ufp" refers to "upstream
		facing port" i.e. port can only act as device.
		"dfp ufp" refers to "dual role port" i.e. the port
		can either be a host port or a device port.

What:		/sys/class/dual_role_usb/.../mode
Date:		June 2015
Contact:	Badhri Jagan Sridharan<badhri@google.com>
Description:
		The mode node refers to the current mode in which the
		port is operating. "dfp" for host ports. "ufp" for device
		ports and "none" when cable is not connected.

		On devices where the USB mode is software-controllable,
		userspace can change the mode by writing "dfp" or "ufp".
		On devices where the USB mode is fixed in hardware,
		this attribute is read-only.

What:		/sys/class/dual_role_usb/.../power_role
Date:		June 2015
Contact:	Badhri Jagan Sridharan<badhri@google.com>
Description:
		The power_role node mentions whether the port
		is "sink"ing or "source"ing power. "none" if
		they are not connected.

		On devices implementing USB Power Delivery,
		userspace can control the power role by writing "sink" or
		"source". On devices without USB-PD, this attribute is
		read-only.

What:		/sys/class/dual_role_usb/.../data_role
Date:		June 2015
Contact:	Badhri Jagan Sridharan<badhri@google.com>
Description:
		The data_role node mentions whether the port
		is acting as "host" or "device" for USB data connection.
		"none" if there is no active data link.

		On devices implementing USB Power Delivery, userspace
		can control the data role by writing "host" or "device".
		On devices without USB-PD, this attribute is read-only

What:		/sys/class/dual_role_usb/.../powers_vconn
Date:		June 2015
Contact:	Badhri Jagan Sridharan<badhri@google.com>
Description:
		The powers_vconn node mentions whether the port
		is supplying power for VCONN pin.

		On devices with software control of VCONN,
		userspace can disable the power supply to VCONN by writing "n",
		or enable the power supply by writing "y".