3 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
5 The /sys/power directory will contain files that will
6 provide a unified interface to the power management
11 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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'
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
26 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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:
66 It will only change to 'firmware' or 'platform' if the system
69 What: /sys/power/image_size
71 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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
88 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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
114 Contact: James Hogan <james@albanarts.com>
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
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
137 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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
150 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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
163 What: /sys/power/reserved_size
165 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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
179 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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
196 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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
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
223 Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
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
238 Contact: Sameer Nanda <snanda@chromium.org>
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.