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Based on kernel version 3.3. Page generated on 2012-03-23 21:23 EST.

1	What:		/sys/power/
2	Date:		August 2006
3	Contact:	Rafael J. Wysocki <rjw@sisk.pl>
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:		August 2006
11	Contact:	Rafael J. Wysocki <rjw@sisk.pl>
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 'standby' (Power-On Suspend), 'mem'
16			(Suspend-to-RAM), and 'disk' (Suspend-to-Disk).
17	
18			Writing to this file one of these strings causes the system to
19			transition into that state. Please see the file
20			Documentation/power/states.txt for a description of each of
21			these states.
22	
23	What:		/sys/power/disk
24	Date:		September 2006
25	Contact:	Rafael J. Wysocki <rjw@sisk.pl>
26	Description:
27			The /sys/power/disk file controls the operating mode of the
28			suspend-to-disk mechanism.  Reading from this file returns
29			the name of the method by which the system will be put to
30			sleep on the next suspend.  There are four methods supported:
31			'firmware' - means that the memory image will be saved to disk
32			by some firmware, in which case we also assume that the
33			firmware will handle the system suspend.
34			'platform' - the memory image will be saved by the kernel and
35			the system will be put to sleep by the platform driver (e.g.
36			ACPI or other PM registers).
37			'shutdown' - the memory image will be saved by the kernel and
38			the system will be powered off.
39			'reboot' - the memory image will be saved by the kernel and
40			the system will be rebooted.
41	
42			Additionally, /sys/power/disk can be used to turn on one of the
43			two testing modes of the suspend-to-disk mechanism: 'testproc'
44			or 'test'.  If the suspend-to-disk mechanism is in the
45			'testproc' mode, writing 'disk' to /sys/power/state will cause
46			the kernel to disable nonboot CPUs and freeze tasks, wait for 5
47			seconds, unfreeze tasks and enable nonboot CPUs.  If it is in
48			the 'test' mode, writing 'disk' to /sys/power/state will cause
49			the kernel to disable nonboot CPUs and freeze tasks, shrink
50			memory, suspend devices, wait for 5 seconds, resume devices,
51			unfreeze tasks and enable nonboot CPUs.  Then, we are able to
52			look in the log messages and work out, for example, which code
53			is being slow and which device drivers are misbehaving.
54	
55			The suspend-to-disk method may be chosen by writing to this
56			file one of the accepted strings:
57	
58			'firmware'
59			'platform'
60			'shutdown'
61			'reboot'
62			'testproc'
63			'test'
64	
65			It will only change to 'firmware' or 'platform' if the system
66			supports that.
67	
68	What:		/sys/power/image_size
69	Date:		August 2006
70	Contact:	Rafael J. Wysocki <rjw@sisk.pl>
71	Description:
72			The /sys/power/image_size file controls the size of the image
73			created by the suspend-to-disk mechanism.  It can be written a
74			string representing a non-negative integer that will be used
75			as an upper limit of the image size, in bytes.  The kernel's
76			suspend-to-disk code will do its best to ensure the image size
77			will not exceed this number.  However, if it turns out to be
78			impossible, the kernel will try to suspend anyway using the
79			smallest image possible.  In particular, if "0" is written to
80			this file, the suspend image will be as small as possible.
81	
82			Reading from this file will display the current image size
83			limit, which is set to 500 MB by default.
84	
85	What:		/sys/power/pm_trace
86	Date:		August 2006
87	Contact:	Rafael J. Wysocki <rjw@sisk.pl>
88	Description:
89			The /sys/power/pm_trace file controls the code which saves the
90			last PM event point in the RTC across reboots, so that you can
91			debug a machine that just hangs during suspend (or more
92			commonly, during resume).  Namely, the RTC is only used to save
93			the last PM event point if this file contains '1'.  Initially
94			it contains '0' which may be changed to '1' by writing a
95			string representing a nonzero integer into it.
96	
97			To use this debugging feature you should attempt to suspend
98			the machine, then reboot it and run
99	
100			dmesg -s 1000000 | grep 'hash matches'
101	
102			If you do not get any matches (or they appear to be false
103			positives), it is possible that the last PM event point
104			referred to a device created by a loadable kernel module.  In
105			this case cat /sys/power/pm_trace_dev_match (see below) after
106			your system is started up and the kernel modules are loaded.
107	
108			CAUTION: Using it will cause your machine's real-time (CMOS)
109			clock to be set to a random invalid time after a resume.
110	
111	What;		/sys/power/pm_trace_dev_match
112	Date:		October 2010
113	Contact:	James Hogan <james@albanarts.com>
114	Description:
115			The /sys/power/pm_trace_dev_match file contains the name of the
116			device associated with the last PM event point saved in the RTC
117			across reboots when pm_trace has been used.  More precisely it
118			contains the list of current devices (including those
119			registered by loadable kernel modules since boot) which match
120			the device hash in the RTC at boot, with a newline after each
121			one.
122	
123			The advantage of this file over the hash matches printed to the
124			kernel log (see /sys/power/pm_trace), is that it includes
125			devices created after boot by loadable kernel modules.
126	
127			Due to the small hash size necessary to fit in the RTC, it is
128			possible that more than one device matches the hash, in which
129			case further investigation is required to determine which
130			device is causing the problem.  Note that genuine RTC clock
131			values (such as when pm_trace has not been used), can still
132			match a device and output it's name here.
133	
134	What:		/sys/power/pm_async
135	Date:		January 2009
136	Contact:	Rafael J. Wysocki <rjw@sisk.pl>
137	Description:
138			The /sys/power/pm_async file controls the switch allowing the
139			user space to enable or disable asynchronous suspend and resume
140			of devices.  If enabled, this feature will cause some device
141			drivers' suspend and resume callbacks to be executed in parallel
142			with each other and with the main suspend thread.  It is enabled
143			if this file contains "1", which is the default.  It may be
144			disabled by writing "0" to this file, in which case all devices
145			will be suspended and resumed synchronously.
146	
147	What:		/sys/power/wakeup_count
148	Date:		July 2010
149	Contact:	Rafael J. Wysocki <rjw@sisk.pl>
150	Description:
151			The /sys/power/wakeup_count file allows user space to put the
152			system into a sleep state while taking into account the
153			concurrent arrival of wakeup events.  Reading from it returns
154			the current number of registered wakeup events and it blocks if
155			some wakeup events are being processed at the time the file is
156			read from.  Writing to it will only succeed if the current
157			number of wakeup events is equal to the written value and, if
158			successful, will make the kernel abort a subsequent transition
159			to a sleep state if any wakeup events are reported after the
160			write has returned.
161	
162	What:		/sys/power/reserved_size
163	Date:		May 2011
164	Contact:	Rafael J. Wysocki <rjw@sisk.pl>
165	Description:
166			The /sys/power/reserved_size file allows user space to control
167			the amount of memory reserved for allocations made by device
168			drivers during the "device freeze" stage of hibernation.  It can
169			be written a string representing a non-negative integer that
170			will be used as the amount of memory to reserve for allocations
171			made by device drivers' "freeze" callbacks, in bytes.
172	
173			Reading from this file will display the current value, which is
174			set to 1 MB by default.
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