What:		/sys/power/
  Date:		August 2006
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power directory will contain files that will
  		provide a unified interface to the power management
  		subsystem.
  
  What:		/sys/power/state
  Date:		August 2006
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/state file controls the 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 these strings causes the system to
  		transition into that state. Please see the file
  		Documentation/power/states.txt for a description of each of
  		these states.
  
  What:		/sys/power/disk
  Date:		September 2006
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/disk file controls the operating mode of the
  		suspend-to-disk mechanism.  Reading from this file returns
  		the name of the method by which the system will be put to
  		sleep on the next suspend.  There are four methods supported:
  		'firmware' - means that the memory image will be saved to disk
  		by some firmware, in which case we also assume that the
  		firmware will handle the system suspend.
  		'platform' - the memory image will be saved by the kernel and
  		the system will be put to sleep by the platform driver (e.g.
  		ACPI or other PM registers).
  		'shutdown' - the memory image will be saved by the kernel and
  		the system will be powered off.
  		'reboot' - the memory image will be saved by the kernel and
  		the system will be rebooted.
  
  		Additionally, /sys/power/disk can be used to turn on one of the
  		two testing modes of the suspend-to-disk mechanism: 'testproc'
  		or 'test'.  If the suspend-to-disk mechanism is in the
  		'testproc' mode, writing 'disk' to /sys/power/state will cause
  		the kernel to disable nonboot CPUs and freeze tasks, wait for 5
  		seconds, unfreeze tasks and enable nonboot CPUs.  If it is in
  		the 'test' mode, writing 'disk' to /sys/power/state will cause
  		the kernel to disable nonboot CPUs and freeze tasks, shrink
  		memory, suspend devices, wait for 5 seconds, resume devices,
  		unfreeze tasks and enable nonboot CPUs.  Then, we are able to
  		look in the log messages and work out, for example, which code
  		is being slow and which device drivers are misbehaving.
  
  		The suspend-to-disk method may be chosen by writing to this
  		file one of the accepted strings:
  
  		'firmware'
  		'platform'
  		'shutdown'
  		'reboot'
  		'testproc'
  		'test'
  
  		It will only change to 'firmware' or 'platform' if the system
  		supports that.
  
  What:		/sys/power/image_size
  Date:		August 2006
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/image_size file controls the size of the image
  		created by the suspend-to-disk mechanism.  It can be written a
  		string representing a non-negative integer that will be used
  		as an upper limit of the image size, in bytes.  The kernel's
  		suspend-to-disk code will do its best to ensure the image size
  		will not exceed this number.  However, if it turns out to be
  		impossible, the kernel will try to suspend anyway using the
  		smallest image possible.  In particular, if "0" is written to
  		this file, the suspend image will be as small as possible.
  
  		Reading from this file will display the current image size
  		limit, which is set to 500 MB by default.
  
  What:		/sys/power/pm_trace
  Date:		August 2006
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/pm_trace file controls the code which saves the
  		last PM event point in the RTC across reboots, so that you can
  		debug a machine that just hangs during suspend (or more
  		commonly, during resume).  Namely, the RTC is only used to save
  		the last PM event point if this file contains '1'.  Initially
  		it contains '0' which may be changed to '1' by writing a
  		string representing a nonzero integer into it.
  
  		To use this debugging feature you should attempt to suspend
  		the machine, then reboot it and run
  
  		dmesg -s 1000000 | grep 'hash matches'
  
  		If you do not get any matches (or they appear to be false
  		positives), it is possible that the last PM event point
  		referred to a device created by a loadable kernel module.  In
  		this case cat /sys/power/pm_trace_dev_match (see below) after
  		your system is started up and the kernel modules are loaded.
  
  		CAUTION: Using it will cause your machine's real-time (CMOS)
  		clock to be set to a random invalid time after a resume.
  
  What;		/sys/power/pm_trace_dev_match
  Date:		October 2010
  Contact:	James Hogan <james@albanarts.com>
  Description:
  		The /sys/power/pm_trace_dev_match file contains the name of the
  		device associated with the last PM event point saved in the RTC
  		across reboots when pm_trace has been used.  More precisely it
  		contains the list of current devices (including those
  		registered by loadable kernel modules since boot) which match
  		the device hash in the RTC at boot, with a newline after each
  		one.
  
  		The advantage of this file over the hash matches printed to the
  		kernel log (see /sys/power/pm_trace), is that it includes
  		devices created after boot by loadable kernel modules.
  
  		Due to the small hash size necessary to fit in the RTC, it is
  		possible that more than one device matches the hash, in which
  		case further investigation is required to determine which
  		device is causing the problem.  Note that genuine RTC clock
  		values (such as when pm_trace has not been used), can still
  		match a device and output it's name here.
  
  What:		/sys/power/pm_async
  Date:		January 2009
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/pm_async file controls the switch allowing the
  		user space to enable or disable asynchronous suspend and resume
  		of devices.  If enabled, this feature will cause some device
  		drivers' suspend and resume callbacks to be executed in parallel
  		with each other and with the main suspend thread.  It is enabled
  		if this file contains "1", which is the default.  It may be
  		disabled by writing "0" to this file, in which case all devices
  		will be suspended and resumed synchronously.
  
  What:		/sys/power/wakeup_count
  Date:		July 2010
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/wakeup_count file allows user space to put the
  		system into a sleep state while taking into account the
  		concurrent arrival of wakeup events.  Reading from it returns
  		the current number of registered wakeup events and it blocks if
  		some wakeup events are being processed at the time the file is
  		read from.  Writing to it will only succeed if the current
  		number of wakeup events is equal to the written value and, if
  		successful, will make the kernel abort a subsequent transition
  		to a sleep state if any wakeup events are reported after the
  		write has returned.
  
  What:		/sys/power/reserved_size
  Date:		May 2011
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/reserved_size file allows user space to control
  		the amount of memory reserved for allocations made by device
  		drivers during the "device freeze" stage of hibernation.  It can
  		be written a string representing a non-negative integer that
  		will be used as the amount of memory to reserve for allocations
  		made by device drivers' "freeze" callbacks, in bytes.
  
  		Reading from this file will display the current value, which is
  		set to 1 MB by default.
  
  What:		/sys/power/autosleep
  Date:		April 2012
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/autosleep file can be written one of the strings
  		returned by reads from /sys/power/state.  If that happens, a
  		work item attempting to trigger a transition of the system to
  		the sleep state represented by that string is queued up.  This
  		attempt will only succeed if there are no active wakeup sources
  		in the system at that time.  After every execution, regardless
  		of whether or not the attempt to put the system to sleep has
  		succeeded, the work item requeues itself until user space
  		writes "off" to /sys/power/autosleep.
  
  		Reading from this file causes the last string successfully
  		written to it to be returned.
  
  What:		/sys/power/wake_lock
  Date:		February 2012
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/wake_lock file allows user space to create
  		wakeup source objects and activate them on demand (if one of
  		those wakeup sources is active, reads from the
  		/sys/power/wakeup_count file block or return false).  When a
  		string without white space is written to /sys/power/wake_lock,
  		it will be assumed to represent a wakeup source name.  If there
  		is a wakeup source object with that name, it will be activated
  		(unless active already).  Otherwise, a new wakeup source object
  		will be registered, assigned the given name and activated.
  		If a string written to /sys/power/wake_lock contains white
  		space, the part of the string preceding the white space will be
  		regarded as a wakeup source name and handled as descrived above.
  		The other part of the string will be regarded as a timeout (in
  		nanoseconds) such that the wakeup source will be automatically
  		deactivated after it has expired.  The timeout, if present, is
  		set regardless of the current state of the wakeup source object
  		in question.
  
  		Reads from this file return a string consisting of the names of
  		wakeup sources created with the help of it that are active at
  		the moment, separated with spaces.
  
  
  What:		/sys/power/wake_unlock
  Date:		February 2012
  Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
  Description:
  		The /sys/power/wake_unlock file allows user space to deactivate
  		wakeup sources created with the help of /sys/power/wake_lock.
  		When a string is written to /sys/power/wake_unlock, it will be
  		assumed to represent the name of a wakeup source to deactivate.
  		If a wakeup source object of that name exists and is active at
  		the moment, it will be deactivated.
  
  		Reads from this file return a string consisting of the names of
  		wakeup sources created with the help of /sys/power/wake_lock
  		that are inactive at the moment, separated with spaces.
  
  What:		/sys/power/pm_print_times
  Date:		May 2012
  Contact:	Sameer Nanda <snanda@chromium.org>
  Description:
  		The /sys/power/pm_print_times file allows user space to
  		control whether the time taken by devices to suspend and
  		resume is printed.  These prints are useful for hunting down
  		devices that take too long to suspend or resume.
  
  		Writing a "1" enables this printing while writing a "0"
  		disables it.  The default value is "0".  Reading from this file
  		will display the current value.