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+Power Management Interface
+
+
+The power management subsystem provides a unified sysfs interface to 
+userspace, regardless of what architecture or platform one is
+running. The interface exists in /sys/power/ directory (assuming sysfs
+is mounted at /sys). 
+
+/sys/power/state controls system power state. Reading from this file
+returns what states are supported, which is hard-coded to 'standby'
+(Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk'
+(Suspend-to-Disk). 
+
+Writing to this file one of those strings causes the system to
+transition into that state. Please see the file
+Documentation/power/states.txt for a description of each of those
+states.
+
+
+/sys/power/disk controls the operating mode of the suspend-to-disk
+mechanism. Suspend-to-disk can be handled in several ways. The
+greatest distinction is who writes memory to disk - the firmware or
+the kernel. If the firmware does it, we assume that it also handles
+suspending the system. 
+
+If the kernel does it, then we have three options for putting the system
+to sleep - using the platform driver (e.g. ACPI or other PM
+registers), powering off the system or rebooting the system (for
+testing). The system will support either 'firmware' or 'platform', and
+that is known a priori. But, the user may choose 'shutdown' or
+'reboot' as alternatives. 
+
+Reading from this file will display what the mode is currently set
+to. Writing to this file will accept one of
+
+       'firmware'
+       'platform'
+       'shutdown'
+       'reboot'
+
+It will only change to 'firmware' or 'platform' if the system supports
+it. 
+