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Based on kernel version 3.15.4. Page generated on 2014-07-07 08:59 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.
9	What:		/sys/power/state
10	Date:		August 2006
11	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
12	Description:
13			The /sys/power/state file controls the system power state.
14			Reading from this file returns what states are supported,
15			which is hard-coded to 'freeze' (Low-Power Idle), 'standby'
16			(Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk'
17			(Suspend-to-Disk).
19			Writing to this file one of these strings causes the system to
20			transition into that state. Please see the file
21			Documentation/power/states.txt for a description of each of
22			these states.
24	What:		/sys/power/disk
25	Date:		September 2006
26	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
27	Description:
28			The /sys/power/disk file controls the operating mode of the
29			suspend-to-disk mechanism.  Reading from this file returns
30			the name of the method by which the system will be put to
31			sleep on the next suspend.  There are four methods supported:
32			'firmware' - means that the memory image will be saved to disk
33			by some firmware, in which case we also assume that the
34			firmware will handle the system suspend.
35			'platform' - the memory image will be saved by the kernel and
36			the system will be put to sleep by the platform driver (e.g.
37			ACPI or other PM registers).
38			'shutdown' - the memory image will be saved by the kernel and
39			the system will be powered off.
40			'reboot' - the memory image will be saved by the kernel and
41			the system will be rebooted.
43			Additionally, /sys/power/disk can be used to turn on one of the
44			two testing modes of the suspend-to-disk mechanism: 'testproc'
45			or 'test'.  If the suspend-to-disk mechanism is in the
46			'testproc' mode, writing 'disk' to /sys/power/state will cause
47			the kernel to disable nonboot CPUs and freeze tasks, wait for 5
48			seconds, unfreeze tasks and enable nonboot CPUs.  If it is in
49			the 'test' mode, writing 'disk' to /sys/power/state will cause
50			the kernel to disable nonboot CPUs and freeze tasks, shrink
51			memory, suspend devices, wait for 5 seconds, resume devices,
52			unfreeze tasks and enable nonboot CPUs.  Then, we are able to
53			look in the log messages and work out, for example, which code
54			is being slow and which device drivers are misbehaving.
56			The suspend-to-disk method may be chosen by writing to this
57			file one of the accepted strings:
59			'firmware'
60			'platform'
61			'shutdown'
62			'reboot'
63			'testproc'
64			'test'
66			It will only change to 'firmware' or 'platform' if the system
67			supports that.
69	What:		/sys/power/image_size
70	Date:		August 2006
71	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
72	Description:
73			The /sys/power/image_size file controls the size of the image
74			created by the suspend-to-disk mechanism.  It can be written a
75			string representing a non-negative integer that will be used
76			as an upper limit of the image size, in bytes.  The kernel's
77			suspend-to-disk code will do its best to ensure the image size
78			will not exceed this number.  However, if it turns out to be
79			impossible, the kernel will try to suspend anyway using the
80			smallest image possible.  In particular, if "0" is written to
81			this file, the suspend image will be as small as possible.
83			Reading from this file will display the current image size
84			limit, which is set to 500 MB by default.
86	What:		/sys/power/pm_trace
87	Date:		August 2006
88	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
89	Description:
90			The /sys/power/pm_trace file controls the code which saves the
91			last PM event point in the RTC across reboots, so that you can
92			debug a machine that just hangs during suspend (or more
93			commonly, during resume).  Namely, the RTC is only used to save
94			the last PM event point if this file contains '1'.  Initially
95			it contains '0' which may be changed to '1' by writing a
96			string representing a nonzero integer into it.
98			To use this debugging feature you should attempt to suspend
99			the machine, then reboot it and run
101			dmesg -s 1000000 | grep 'hash matches'
103			If you do not get any matches (or they appear to be false
104			positives), it is possible that the last PM event point
105			referred to a device created by a loadable kernel module.  In
106			this case cat /sys/power/pm_trace_dev_match (see below) after
107			your system is started up and the kernel modules are loaded.
109			CAUTION: Using it will cause your machine's real-time (CMOS)
110			clock to be set to a random invalid time after a resume.
112	What;		/sys/power/pm_trace_dev_match
113	Date:		October 2010
114	Contact:	James Hogan <james@albanarts.com>
115	Description:
116			The /sys/power/pm_trace_dev_match file contains the name of the
117			device associated with the last PM event point saved in the RTC
118			across reboots when pm_trace has been used.  More precisely it
119			contains the list of current devices (including those
120			registered by loadable kernel modules since boot) which match
121			the device hash in the RTC at boot, with a newline after each
122			one.
124			The advantage of this file over the hash matches printed to the
125			kernel log (see /sys/power/pm_trace), is that it includes
126			devices created after boot by loadable kernel modules.
128			Due to the small hash size necessary to fit in the RTC, it is
129			possible that more than one device matches the hash, in which
130			case further investigation is required to determine which
131			device is causing the problem.  Note that genuine RTC clock
132			values (such as when pm_trace has not been used), can still
133			match a device and output it's name here.
135	What:		/sys/power/pm_async
136	Date:		January 2009
137	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
138	Description:
139			The /sys/power/pm_async file controls the switch allowing the
140			user space to enable or disable asynchronous suspend and resume
141			of devices.  If enabled, this feature will cause some device
142			drivers' suspend and resume callbacks to be executed in parallel
143			with each other and with the main suspend thread.  It is enabled
144			if this file contains "1", which is the default.  It may be
145			disabled by writing "0" to this file, in which case all devices
146			will be suspended and resumed synchronously.
148	What:		/sys/power/wakeup_count
149	Date:		July 2010
150	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
151	Description:
152			The /sys/power/wakeup_count file allows user space to put the
153			system into a sleep state while taking into account the
154			concurrent arrival of wakeup events.  Reading from it returns
155			the current number of registered wakeup events and it blocks if
156			some wakeup events are being processed at the time the file is
157			read from.  Writing to it will only succeed if the current
158			number of wakeup events is equal to the written value and, if
159			successful, will make the kernel abort a subsequent transition
160			to a sleep state if any wakeup events are reported after the
161			write has returned.
163	What:		/sys/power/reserved_size
164	Date:		May 2011
165	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
166	Description:
167			The /sys/power/reserved_size file allows user space to control
168			the amount of memory reserved for allocations made by device
169			drivers during the "device freeze" stage of hibernation.  It can
170			be written a string representing a non-negative integer that
171			will be used as the amount of memory to reserve for allocations
172			made by device drivers' "freeze" callbacks, in bytes.
174			Reading from this file will display the current value, which is
175			set to 1 MB by default.
177	What:		/sys/power/autosleep
178	Date:		April 2012
179	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
180	Description:
181			The /sys/power/autosleep file can be written one of the strings
182			returned by reads from /sys/power/state.  If that happens, a
183			work item attempting to trigger a transition of the system to
184			the sleep state represented by that string is queued up.  This
185			attempt will only succeed if there are no active wakeup sources
186			in the system at that time.  After every execution, regardless
187			of whether or not the attempt to put the system to sleep has
188			succeeded, the work item requeues itself until user space
189			writes "off" to /sys/power/autosleep.
191			Reading from this file causes the last string successfully
192			written to it to be returned.
194	What:		/sys/power/wake_lock
195	Date:		February 2012
196	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
197	Description:
198			The /sys/power/wake_lock file allows user space to create
199			wakeup source objects and activate them on demand (if one of
200			those wakeup sources is active, reads from the
201			/sys/power/wakeup_count file block or return false).  When a
202			string without white space is written to /sys/power/wake_lock,
203			it will be assumed to represent a wakeup source name.  If there
204			is a wakeup source object with that name, it will be activated
205			(unless active already).  Otherwise, a new wakeup source object
206			will be registered, assigned the given name and activated.
207			If a string written to /sys/power/wake_lock contains white
208			space, the part of the string preceding the white space will be
209			regarded as a wakeup source name and handled as descrived above.
210			The other part of the string will be regarded as a timeout (in
211			nanoseconds) such that the wakeup source will be automatically
212			deactivated after it has expired.  The timeout, if present, is
213			set regardless of the current state of the wakeup source object
214			in question.
216			Reads from this file return a string consisting of the names of
217			wakeup sources created with the help of it that are active at
218			the moment, separated with spaces.
221	What:		/sys/power/wake_unlock
222	Date:		February 2012
223	Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
224	Description:
225			The /sys/power/wake_unlock file allows user space to deactivate
226			wakeup sources created with the help of /sys/power/wake_lock.
227			When a string is written to /sys/power/wake_unlock, it will be
228			assumed to represent the name of a wakeup source to deactivate.
229			If a wakeup source object of that name exists and is active at
230			the moment, it will be deactivated.
232			Reads from this file return a string consisting of the names of
233			wakeup sources created with the help of /sys/power/wake_lock
234			that are inactive at the moment, separated with spaces.
236	What:		/sys/power/pm_print_times
237	Date:		May 2012
238	Contact:	Sameer Nanda <snanda@chromium.org>
239	Description:
240			The /sys/power/pm_print_times file allows user space to
241			control whether the time taken by devices to suspend and
242			resume is printed.  These prints are useful for hunting down
243			devices that take too long to suspend or resume.
245			Writing a "1" enables this printing while writing a "0"
246			disables it.  The default value is "0".  Reading from this file
247			will display the current value.
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