+X - Specifying Device Power Management Information (sleep property)
+===================================================================
+
+Devices on SOCs often have mechanisms for placing devices into low-power
+states that are decoupled from the devices' own register blocks. Sometimes,
+this information is more complicated than a cell-index property can
+reasonably describe. Thus, each device controlled in such a manner
+may contain a "sleep" property which describes these connections.
+
+The sleep property consists of one or more sleep resources, each of
+which consists of a phandle to a sleep controller, followed by a
+controller-specific sleep specifier of zero or more cells.
+
+The semantics of what type of low power modes are possible are defined
+by the sleep controller. Some examples of the types of low power modes
+that may be supported are:
+
+ - Dynamic: The device may be disabled or enabled at any time.
+ - System Suspend: The device may request to be disabled or remain
+ awake during system suspend, but will not be disabled until then.
+ - Permanent: The device is disabled permanently (until the next hard
+ reset).
+
+Some devices may share a clock domain with each other, such that they should
+only be suspended when none of the devices are in use. Where reasonable,
+such nodes should be placed on a virtual bus, where the bus has the sleep
+property. If the clock domain is shared among devices that cannot be
+reasonably grouped in this manner, then create a virtual sleep controller
+(similar to an interrupt nexus, except that defining a standardized
+sleep-map should wait until its necessity is demonstrated).
+