Documentation/ABI/testing/sysfs-power

   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.
   8
   9 What:           /sys/power/state
  10 Date:           November 2016
  11 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  12 Description:
  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" (suspend), "standby" (power-on
  16                 suspend), "freeze" (suspend-to-idle) and "disk" (hibernation).
  17
  18                 Writing one of the above strings to this file causes the system
  19                 to transition into the corresponding state, if available.
  20
  21                 See Documentation/power/states.txt for more information.
  22
  23 What:           /sys/power/mem_sleep
  24 Date:           November 2016
  25 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  26 Description:
  27                 The /sys/power/mem_sleep file controls the operating mode of
  28                 system suspend.  Reading from it returns the available modes
  29                 as "s2idle" (always present), "shallow" and "deep" (present if
  30                 supported).  The mode that will be used on subsequent attempts
  31                 to suspend the system (by writing "mem" to the /sys/power/state
  32                 file described above) is enclosed in square brackets.
  33
  34                 Writing one of the above strings to this file causes the mode
  35                 represented by it to be used on subsequent attempts to suspend
  36                 the system.
  37
  38                 See Documentation/power/states.txt for more information.
  39
  40 What:           /sys/power/disk
  41 Date:           September 2006
  42 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  43 Description:
  44                 The /sys/power/disk file controls the operating mode of the
  45                 suspend-to-disk mechanism.  Reading from this file returns
  46                 the name of the method by which the system will be put to
  47                 sleep on the next suspend.  There are four methods supported:
  48                 'firmware' - means that the memory image will be saved to disk
  49                 by some firmware, in which case we also assume that the
  50                 firmware will handle the system suspend.
  51                 'platform' - the memory image will be saved by the kernel and
  52                 the system will be put to sleep by the platform driver (e.g.
  53                 ACPI or other PM registers).
  54                 'shutdown' - the memory image will be saved by the kernel and
  55                 the system will be powered off.
  56                 'reboot' - the memory image will be saved by the kernel and
  57                 the system will be rebooted.
  58
  59                 Additionally, /sys/power/disk can be used to turn on one of the
  60                 two testing modes of the suspend-to-disk mechanism: 'testproc'
  61                 or 'test'.  If the suspend-to-disk mechanism is in the
  62                 'testproc' mode, writing 'disk' to /sys/power/state will cause
  63                 the kernel to disable nonboot CPUs and freeze tasks, wait for 5
  64                 seconds, unfreeze tasks and enable nonboot CPUs.  If it is in
  65                 the 'test' mode, writing 'disk' to /sys/power/state will cause
  66                 the kernel to disable nonboot CPUs and freeze tasks, shrink
  67                 memory, suspend devices, wait for 5 seconds, resume devices,
  68                 unfreeze tasks and enable nonboot CPUs.  Then, we are able to
  69                 look in the log messages and work out, for example, which code
  70                 is being slow and which device drivers are misbehaving.
  71
  72                 The suspend-to-disk method may be chosen by writing to this
  73                 file one of the accepted strings:
  74
  75                 'firmware'
  76                 'platform'
  77                 'shutdown'
  78                 'reboot'
  79                 'testproc'
  80                 'test'
  81
  82                 It will only change to 'firmware' or 'platform' if the system
  83                 supports that.
  84
  85 What:           /sys/power/image_size
  86 Date:           August 2006
  87 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  88 Description:
  89                 The /sys/power/image_size file controls the size of the image
  90                 created by the suspend-to-disk mechanism.  It can be written a
  91                 string representing a non-negative integer that will be used
  92                 as an upper limit of the image size, in bytes.  The kernel's
  93                 suspend-to-disk code will do its best to ensure the image size
  94                 will not exceed this number.  However, if it turns out to be
  95                 impossible, the kernel will try to suspend anyway using the
  96                 smallest image possible.  In particular, if "0" is written to
  97                 this file, the suspend image will be as small as possible.
  98
  99                 Reading from this file will display the current image size
 100                 limit, which is set to 500 MB by default.
 101
 102 What:           /sys/power/pm_trace
 103 Date:           August 2006
 104 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 105 Description:
 106                 The /sys/power/pm_trace file controls the code which saves the
 107                 last PM event point in the RTC across reboots, so that you can
 108                 debug a machine that just hangs during suspend (or more
 109                 commonly, during resume).  Namely, the RTC is only used to save
 110                 the last PM event point if this file contains '1'.  Initially
 111                 it contains '0' which may be changed to '1' by writing a
 112                 string representing a nonzero integer into it.
 113
 114                 To use this debugging feature you should attempt to suspend
 115                 the machine, then reboot it and run
 116
 117                 dmesg -s 1000000 | grep 'hash matches'
 118
 119                 If you do not get any matches (or they appear to be false
 120                 positives), it is possible that the last PM event point
 121                 referred to a device created by a loadable kernel module.  In
 122                 this case cat /sys/power/pm_trace_dev_match (see below) after
 123                 your system is started up and the kernel modules are loaded.
 124
 125                 CAUTION: Using it will cause your machine's real-time (CMOS)
 126                 clock to be set to a random invalid time after a resume.
 127
 128 What;           /sys/power/pm_trace_dev_match
 129 Date:           October 2010
 130 Contact:        James Hogan <james@albanarts.com>
 131 Description:
 132                 The /sys/power/pm_trace_dev_match file contains the name of the
 133                 device associated with the last PM event point saved in the RTC
 134                 across reboots when pm_trace has been used.  More precisely it
 135                 contains the list of current devices (including those
 136                 registered by loadable kernel modules since boot) which match
 137                 the device hash in the RTC at boot, with a newline after each
 138                 one.
 139
 140                 The advantage of this file over the hash matches printed to the
 141                 kernel log (see /sys/power/pm_trace), is that it includes
 142                 devices created after boot by loadable kernel modules.
 143
 144                 Due to the small hash size necessary to fit in the RTC, it is
 145                 possible that more than one device matches the hash, in which
 146                 case further investigation is required to determine which
 147                 device is causing the problem.  Note that genuine RTC clock
 148                 values (such as when pm_trace has not been used), can still
 149                 match a device and output it's name here.
 150
 151 What:           /sys/power/pm_async
 152 Date:           January 2009
 153 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 154 Description:
 155                 The /sys/power/pm_async file controls the switch allowing the
 156                 user space to enable or disable asynchronous suspend and resume
 157                 of devices.  If enabled, this feature will cause some device
 158                 drivers' suspend and resume callbacks to be executed in parallel
 159                 with each other and with the main suspend thread.  It is enabled
 160                 if this file contains "1", which is the default.  It may be
 161                 disabled by writing "0" to this file, in which case all devices
 162                 will be suspended and resumed synchronously.
 163
 164 What:           /sys/power/wakeup_count
 165 Date:           July 2010
 166 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 167 Description:
 168                 The /sys/power/wakeup_count file allows user space to put the
 169                 system into a sleep state while taking into account the
 170                 concurrent arrival of wakeup events.  Reading from it returns
 171                 the current number of registered wakeup events and it blocks if
 172                 some wakeup events are being processed at the time the file is
 173                 read from.  Writing to it will only succeed if the current
 174                 number of wakeup events is equal to the written value and, if
 175                 successful, will make the kernel abort a subsequent transition
 176                 to a sleep state if any wakeup events are reported after the
 177                 write has returned.
 178
 179 What:           /sys/power/reserved_size
 180 Date:           May 2011
 181 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 182 Description:
 183                 The /sys/power/reserved_size file allows user space to control
 184                 the amount of memory reserved for allocations made by device
 185                 drivers during the "device freeze" stage of hibernation.  It can
 186                 be written a string representing a non-negative integer that
 187                 will be used as the amount of memory to reserve for allocations
 188                 made by device drivers' "freeze" callbacks, in bytes.
 189
 190                 Reading from this file will display the current value, which is
 191                 set to 1 MB by default.
 192
 193 What:           /sys/power/autosleep
 194 Date:           April 2012
 195 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 196 Description:
 197                 The /sys/power/autosleep file can be written one of the strings
 198                 returned by reads from /sys/power/state.  If that happens, a
 199                 work item attempting to trigger a transition of the system to
 200                 the sleep state represented by that string is queued up.  This
 201                 attempt will only succeed if there are no active wakeup sources
 202                 in the system at that time.  After every execution, regardless
 203                 of whether or not the attempt to put the system to sleep has
 204                 succeeded, the work item requeues itself until user space
 205                 writes "off" to /sys/power/autosleep.
 206
 207                 Reading from this file causes the last string successfully
 208                 written to it to be returned.
 209
 210 What:           /sys/power/wake_lock
 211 Date:           February 2012
 212 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 213 Description:
 214                 The /sys/power/wake_lock file allows user space to create
 215                 wakeup source objects and activate them on demand (if one of
 216                 those wakeup sources is active, reads from the
 217                 /sys/power/wakeup_count file block or return false).  When a
 218                 string without white space is written to /sys/power/wake_lock,
 219                 it will be assumed to represent a wakeup source name.  If there
 220                 is a wakeup source object with that name, it will be activated
 221                 (unless active already).  Otherwise, a new wakeup source object
 222                 will be registered, assigned the given name and activated.
 223                 If a string written to /sys/power/wake_lock contains white
 224                 space, the part of the string preceding the white space will be
 225                 regarded as a wakeup source name and handled as descrived above.
 226                 The other part of the string will be regarded as a timeout (in
 227                 nanoseconds) such that the wakeup source will be automatically
 228                 deactivated after it has expired.  The timeout, if present, is
 229                 set regardless of the current state of the wakeup source object
 230                 in question.
 231
 232                 Reads from this file return a string consisting of the names of
 233                 wakeup sources created with the help of it that are active at
 234                 the moment, separated with spaces.
 235
 236
 237 What:           /sys/power/wake_unlock
 238 Date:           February 2012
 239 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 240 Description:
 241                 The /sys/power/wake_unlock file allows user space to deactivate
 242                 wakeup sources created with the help of /sys/power/wake_lock.
 243                 When a string is written to /sys/power/wake_unlock, it will be
 244                 assumed to represent the name of a wakeup source to deactivate.
 245                 If a wakeup source object of that name exists and is active at
 246                 the moment, it will be deactivated.
 247
 248                 Reads from this file return a string consisting of the names of
 249                 wakeup sources created with the help of /sys/power/wake_lock
 250                 that are inactive at the moment, separated with spaces.
 251
 252 What:           /sys/power/pm_print_times
 253 Date:           May 2012
 254 Contact:        Sameer Nanda <snanda@chromium.org>
 255 Description:
 256                 The /sys/power/pm_print_times file allows user space to
 257                 control whether the time taken by devices to suspend and
 258                 resume is printed.  These prints are useful for hunting down
 259                 devices that take too long to suspend or resume.
 260
 261                 Writing a "1" enables this printing while writing a "0"
 262                 disables it.  The default value is "0".  Reading from this file
 263                 will display the current value.
 264
 265 What:           /sys/power/pm_wakeup_irq
 266 Date:           April 2015
 267 Contact:        Alexandra Yates <alexandra.yates@linux.intel.org>
 268 Description:
 269                 The /sys/power/pm_wakeup_irq file reports to user space the IRQ
 270                 number of the first wakeup interrupt (that is, the first
 271                 interrupt from an IRQ line armed for system wakeup) seen by the
 272                 kernel during the most recent system suspend/resume cycle.
 273
 274                 This output is useful for system wakeup diagnostics of spurious
 275                 wakeup interrupts.