What:		/sys/devices/.../power_state
Date:		January 2013
Contact:	Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Description:
		The /sys/devices/.../power_state attribute is only present for
		device objects representing ACPI device nodes that provide power
		management methods.

		If present, it contains a string representing the current ACPI
		power state of the given device node.  Its possible values,
		"D0", "D1", "D2", "D3hot", and "D3cold", reflect the power state
		names defined by the ACPI specification (ACPI 4 and above).

		If the device node uses shared ACPI power resources, this state
		determines a list of power resources required not to be turned
		off.  However, some power resources needed by the device node in
		higher-power (lower-number) states may also be ON because of
		some other devices using them at the moment.

		This attribute is read-only.