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Based on kernel version 3.16. Page generated on 2014-08-06 21:36 EST.

1	What:		/sys/power/
2	Date:		August 2006
3	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
4	Description:
5			The /sys/power directory will contain files that will
6			provide a unified interface to the power management
7			subsystem.
8	
9	What:		/sys/power/state
10	Date:		May 2014
11	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
12	Description:
13			The /sys/power/state file controls system sleep states.
14			Reading from this file returns the available sleep state
15			labels, which may be "mem", "standby", "freeze" and "disk"
16			(hibernation).  The meanings of the first three labels depend on
17			the relative_sleep_states command line argument as follows:
18			 1) relative_sleep_states = 1
19			    "mem", "standby", "freeze" represent non-hibernation sleep
20			    states from the deepest ("mem", always present) to the
21			    shallowest ("freeze").  "standby" and "freeze" may or may
22			    not be present depending on the capabilities of the
23			    platform.  "freeze" can only be present if "standby" is
24			    present.
25			 2) relative_sleep_states = 0 (default)
26			    "mem" - "suspend-to-RAM", present if supported.
27			    "standby" - "power-on suspend", present if supported.
28			    "freeze" - "suspend-to-idle", always present.
29	
30			Writing to this file one of these strings causes the system to
31			transition into the corresponding state, if available.  See
32			Documentation/power/states.txt for a description of what
33			"suspend-to-RAM", "power-on suspend" and "suspend-to-idle" mean.
34	
35	What:		/sys/power/disk
36	Date:		September 2006
37	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
38	Description:
39			The /sys/power/disk file controls the operating mode of the
40			suspend-to-disk mechanism.  Reading from this file returns
41			the name of the method by which the system will be put to
42			sleep on the next suspend.  There are four methods supported:
43			'firmware' - means that the memory image will be saved to disk
44			by some firmware, in which case we also assume that the
45			firmware will handle the system suspend.
46			'platform' - the memory image will be saved by the kernel and
47			the system will be put to sleep by the platform driver (e.g.
48			ACPI or other PM registers).
49			'shutdown' - the memory image will be saved by the kernel and
50			the system will be powered off.
51			'reboot' - the memory image will be saved by the kernel and
52			the system will be rebooted.
53	
54			Additionally, /sys/power/disk can be used to turn on one of the
55			two testing modes of the suspend-to-disk mechanism: 'testproc'
56			or 'test'.  If the suspend-to-disk mechanism is in the
57			'testproc' mode, writing 'disk' to /sys/power/state will cause
58			the kernel to disable nonboot CPUs and freeze tasks, wait for 5
59			seconds, unfreeze tasks and enable nonboot CPUs.  If it is in
60			the 'test' mode, writing 'disk' to /sys/power/state will cause
61			the kernel to disable nonboot CPUs and freeze tasks, shrink
62			memory, suspend devices, wait for 5 seconds, resume devices,
63			unfreeze tasks and enable nonboot CPUs.  Then, we are able to
64			look in the log messages and work out, for example, which code
65			is being slow and which device drivers are misbehaving.
66	
67			The suspend-to-disk method may be chosen by writing to this
68			file one of the accepted strings:
69	
70			'firmware'
71			'platform'
72			'shutdown'
73			'reboot'
74			'testproc'
75			'test'
76	
77			It will only change to 'firmware' or 'platform' if the system
78			supports that.
79	
80	What:		/sys/power/image_size
81	Date:		August 2006
82	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
83	Description:
84			The /sys/power/image_size file controls the size of the image
85			created by the suspend-to-disk mechanism.  It can be written a
86			string representing a non-negative integer that will be used
87			as an upper limit of the image size, in bytes.  The kernel's
88			suspend-to-disk code will do its best to ensure the image size
89			will not exceed this number.  However, if it turns out to be
90			impossible, the kernel will try to suspend anyway using the
91			smallest image possible.  In particular, if "0" is written to
92			this file, the suspend image will be as small as possible.
93	
94			Reading from this file will display the current image size
95			limit, which is set to 500 MB by default.
96	
97	What:		/sys/power/pm_trace
98	Date:		August 2006
99	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
100	Description:
101			The /sys/power/pm_trace file controls the code which saves the
102			last PM event point in the RTC across reboots, so that you can
103			debug a machine that just hangs during suspend (or more
104			commonly, during resume).  Namely, the RTC is only used to save
105			the last PM event point if this file contains '1'.  Initially
106			it contains '0' which may be changed to '1' by writing a
107			string representing a nonzero integer into it.
108	
109			To use this debugging feature you should attempt to suspend
110			the machine, then reboot it and run
111	
112			dmesg -s 1000000 | grep 'hash matches'
113	
114			If you do not get any matches (or they appear to be false
115			positives), it is possible that the last PM event point
116			referred to a device created by a loadable kernel module.  In
117			this case cat /sys/power/pm_trace_dev_match (see below) after
118			your system is started up and the kernel modules are loaded.
119	
120			CAUTION: Using it will cause your machine's real-time (CMOS)
121			clock to be set to a random invalid time after a resume.
122	
123	What;		/sys/power/pm_trace_dev_match
124	Date:		October 2010
125	Contact:	James Hogan <james@albanarts.com>
126	Description:
127			The /sys/power/pm_trace_dev_match file contains the name of the
128			device associated with the last PM event point saved in the RTC
129			across reboots when pm_trace has been used.  More precisely it
130			contains the list of current devices (including those
131			registered by loadable kernel modules since boot) which match
132			the device hash in the RTC at boot, with a newline after each
133			one.
134	
135			The advantage of this file over the hash matches printed to the
136			kernel log (see /sys/power/pm_trace), is that it includes
137			devices created after boot by loadable kernel modules.
138	
139			Due to the small hash size necessary to fit in the RTC, it is
140			possible that more than one device matches the hash, in which
141			case further investigation is required to determine which
142			device is causing the problem.  Note that genuine RTC clock
143			values (such as when pm_trace has not been used), can still
144			match a device and output it's name here.
145	
146	What:		/sys/power/pm_async
147	Date:		January 2009
148	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
149	Description:
150			The /sys/power/pm_async file controls the switch allowing the
151			user space to enable or disable asynchronous suspend and resume
152			of devices.  If enabled, this feature will cause some device
153			drivers' suspend and resume callbacks to be executed in parallel
154			with each other and with the main suspend thread.  It is enabled
155			if this file contains "1", which is the default.  It may be
156			disabled by writing "0" to this file, in which case all devices
157			will be suspended and resumed synchronously.
158	
159	What:		/sys/power/wakeup_count
160	Date:		July 2010
161	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
162	Description:
163			The /sys/power/wakeup_count file allows user space to put the
164			system into a sleep state while taking into account the
165			concurrent arrival of wakeup events.  Reading from it returns
166			the current number of registered wakeup events and it blocks if
167			some wakeup events are being processed at the time the file is
168			read from.  Writing to it will only succeed if the current
169			number of wakeup events is equal to the written value and, if
170			successful, will make the kernel abort a subsequent transition
171			to a sleep state if any wakeup events are reported after the
172			write has returned.
173	
174	What:		/sys/power/reserved_size
175	Date:		May 2011
176	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
177	Description:
178			The /sys/power/reserved_size file allows user space to control
179			the amount of memory reserved for allocations made by device
180			drivers during the "device freeze" stage of hibernation.  It can
181			be written a string representing a non-negative integer that
182			will be used as the amount of memory to reserve for allocations
183			made by device drivers' "freeze" callbacks, in bytes.
184	
185			Reading from this file will display the current value, which is
186			set to 1 MB by default.
187	
188	What:		/sys/power/autosleep
189	Date:		April 2012
190	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
191	Description:
192			The /sys/power/autosleep file can be written one of the strings
193			returned by reads from /sys/power/state.  If that happens, a
194			work item attempting to trigger a transition of the system to
195			the sleep state represented by that string is queued up.  This
196			attempt will only succeed if there are no active wakeup sources
197			in the system at that time.  After every execution, regardless
198			of whether or not the attempt to put the system to sleep has
199			succeeded, the work item requeues itself until user space
200			writes "off" to /sys/power/autosleep.
201	
202			Reading from this file causes the last string successfully
203			written to it to be returned.
204	
205	What:		/sys/power/wake_lock
206	Date:		February 2012
207	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
208	Description:
209			The /sys/power/wake_lock file allows user space to create
210			wakeup source objects and activate them on demand (if one of
211			those wakeup sources is active, reads from the
212			/sys/power/wakeup_count file block or return false).  When a
213			string without white space is written to /sys/power/wake_lock,
214			it will be assumed to represent a wakeup source name.  If there
215			is a wakeup source object with that name, it will be activated
216			(unless active already).  Otherwise, a new wakeup source object
217			will be registered, assigned the given name and activated.
218			If a string written to /sys/power/wake_lock contains white
219			space, the part of the string preceding the white space will be
220			regarded as a wakeup source name and handled as descrived above.
221			The other part of the string will be regarded as a timeout (in
222			nanoseconds) such that the wakeup source will be automatically
223			deactivated after it has expired.  The timeout, if present, is
224			set regardless of the current state of the wakeup source object
225			in question.
226	
227			Reads from this file return a string consisting of the names of
228			wakeup sources created with the help of it that are active at
229			the moment, separated with spaces.
230	
231	
232	What:		/sys/power/wake_unlock
233	Date:		February 2012
234	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
235	Description:
236			The /sys/power/wake_unlock file allows user space to deactivate
237			wakeup sources created with the help of /sys/power/wake_lock.
238			When a string is written to /sys/power/wake_unlock, it will be
239			assumed to represent the name of a wakeup source to deactivate.
240			If a wakeup source object of that name exists and is active at
241			the moment, it will be deactivated.
242	
243			Reads from this file return a string consisting of the names of
244			wakeup sources created with the help of /sys/power/wake_lock
245			that are inactive at the moment, separated with spaces.
246	
247	What:		/sys/power/pm_print_times
248	Date:		May 2012
249	Contact:	Sameer Nanda <snanda@chromium.org>
250	Description:
251			The /sys/power/pm_print_times file allows user space to
252			control whether the time taken by devices to suspend and
253			resume is printed.  These prints are useful for hunting down
254			devices that take too long to suspend or resume.
255	
256			Writing a "1" enables this printing while writing a "0"
257			disables it.  The default value is "0".  Reading from this file
258			will display the current value.
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