1What: /sys/power/ 2Date: August 2006 3Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 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: May 2014 11Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 12Description: 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 35What: /sys/power/disk 36Date: September 2006 37Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 38Description: 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 80What: /sys/power/image_size 81Date: August 2006 82Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 83Description: 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 97What: /sys/power/pm_trace 98Date: August 2006 99Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 100Description: 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 123What; /sys/power/pm_trace_dev_match 124Date: October 2010 125Contact: James Hogan <james@albanarts.com> 126Description: 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 146What: /sys/power/pm_async 147Date: January 2009 148Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 149Description: 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 159What: /sys/power/wakeup_count 160Date: July 2010 161Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 162Description: 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 174What: /sys/power/reserved_size 175Date: May 2011 176Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 177Description: 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 188What: /sys/power/autosleep 189Date: April 2012 190Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 191Description: 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 205What: /sys/power/wake_lock 206Date: February 2012 207Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 208Description: 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 232What: /sys/power/wake_unlock 233Date: February 2012 234Contact: Rafael J. Wysocki <rjw@rjwysocki.net> 235Description: 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 247What: /sys/power/pm_print_times 248Date: May 2012 249Contact: Sameer Nanda <snanda@chromium.org> 250Description: 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. 259