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Rafael J. Wysocki84ed64e2006-08-30 23:38:06 +02001What: /sys/power/
2Date: August 2006
3Contact: Rafael J. Wysocki <rjw@sisk.pl>
4Description:
5 The /sys/power directory will contain files that will
6 provide a unified interface to the power management
7 subsystem.
8
9What: /sys/power/state
10Date: August 2006
11Contact: Rafael J. Wysocki <rjw@sisk.pl>
12Description:
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
23What: /sys/power/disk
Rafael J. Wysockib918f6e2006-11-02 22:07:19 -080024Date: September 2006
Rafael J. Wysocki84ed64e2006-08-30 23:38:06 +020025Contact: Rafael J. Wysocki <rjw@sisk.pl>
26Description:
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
Rafael J. Wysockib918f6e2006-11-02 22:07:19 -080042 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
Rafael J. Wysocki84ed64e2006-08-30 23:38:06 +020055 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'
Rafael J. Wysockib918f6e2006-11-02 22:07:19 -080062 'testproc'
63 'test'
Rafael J. Wysocki84ed64e2006-08-30 23:38:06 +020064
65 It will only change to 'firmware' or 'platform' if the system
66 supports that.
67
68What: /sys/power/image_size
69Date: August 2006
70Contact: Rafael J. Wysocki <rjw@sisk.pl>
71Description:
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
85What: /sys/power/pm_trace
86Date: August 2006
87Contact: Rafael J. Wysocki <rjw@sisk.pl>
88Description:
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
James Hogand33ac602010-10-12 00:00:25 +0200102 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
Rafael J. Wysocki84ed64e2006-08-30 23:38:06 +0200108 CAUTION: Using it will cause your machine's real-time (CMOS)
109 clock to be set to a random invalid time after a resume.
Rafael J. Wysocki0e06b4a2010-01-23 22:25:15 +0100110
James Hogand33ac602010-10-12 00:00:25 +0200111What; /sys/power/pm_trace_dev_match
112Date: October 2010
113Contact: James Hogan <james@albanarts.com>
114Description:
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
Rafael J. Wysocki0e06b4a2010-01-23 22:25:15 +0100134What: /sys/power/pm_async
135Date: January 2009
136Contact: Rafael J. Wysocki <rjw@sisk.pl>
137Description:
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.
Rafael J. Wysockic125e962010-07-05 22:43:53 +0200146
147What: /sys/power/wakeup_count
148Date: July 2010
149Contact: Rafael J. Wysocki <rjw@sisk.pl>
150Description:
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.
Rafael J. Wysockiddeb6482011-05-15 11:38:48 +0200161
162What: /sys/power/reserved_size
163Date: May 2011
164Contact: Rafael J. Wysocki <rjw@sisk.pl>
165Description:
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.
Rafael J. Wysocki7483b4a2012-04-29 22:53:22 +0200175
176What: /sys/power/autosleep
177Date: April 2012
178Contact: Rafael J. Wysocki <rjw@sisk.pl>
179Description:
180 The /sys/power/autosleep file can be written one of the strings
181 returned by reads from /sys/power/state. If that happens, a
182 work item attempting to trigger a transition of the system to
183 the sleep state represented by that string is queued up. This
184 attempt will only succeed if there are no active wakeup sources
185 in the system at that time. After every execution, regardless
186 of whether or not the attempt to put the system to sleep has
187 succeeded, the work item requeues itself until user space
188 writes "off" to /sys/power/autosleep.
189
190 Reading from this file causes the last string successfully
191 written to it to be returned.