Documentation/ABI/testing/sysfs-devices-power

   1 What:           /sys/devices/.../power/
   2 Date:           January 2009
   3 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
   4 Description:
   5                 The /sys/devices/.../power directory contains attributes
   6                 allowing the user space to check and modify some power
   7                 management related properties of given device.
   8
   9 What:           /sys/devices/.../power/wakeup
  10 Date:           January 2009
  11 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  12 Description:
  13                 The /sys/devices/.../power/wakeup attribute allows the user
  14                 space to check if the device is enabled to wake up the system
  15                 from sleep states, such as the memory sleep state (suspend to
  16                 RAM) and hibernation (suspend to disk), and to enable or disable
  17                 it to do that as desired.
  18
  19                 Some devices support "wakeup" events, which are hardware signals
  20                 used to activate the system from a sleep state.  Such devices
  21                 have one of the following two values for the sysfs power/wakeup
  22                 file:
  23
  24                 + "enabled\n" to issue the events;
  25                 + "disabled\n" not to do so;
  26
  27                 In that cases the user space can change the setting represented
  28                 by the contents of this file by writing either "enabled", or
  29                 "disabled" to it.
  30
  31                 For the devices that are not capable of generating system wakeup
  32                 events this file is not present.  In that case the device cannot
  33                 be enabled to wake up the system from sleep states.
  34
  35 What:           /sys/devices/.../power/control
  36 Date:           January 2009
  37 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  38 Description:
  39                 The /sys/devices/.../power/control attribute allows the user
  40                 space to control the run-time power management of the device.
  41
  42                 All devices have one of the following two values for the
  43                 power/control file:
  44
  45                 + "auto\n" to allow the device to be power managed at run time;
  46                 + "on\n" to prevent the device from being power managed;
  47
  48                 The default for all devices is "auto", which means that they may
  49                 be subject to automatic power management, depending on their
  50                 drivers.  Changing this attribute to "on" prevents the driver
  51                 from power managing the device at run time.  Doing that while
  52                 the device is suspended causes it to be woken up.
  53
  54 What:           /sys/devices/.../power/async
  55 Date:           January 2009
  56 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  57 Description:
  58                 The /sys/devices/.../async attribute allows the user space to
  59                 enable or diasble the device's suspend and resume callbacks to
  60                 be executed asynchronously (ie. in separate threads, in parallel
  61                 with the main suspend/resume thread) during system-wide power
  62                 transitions (eg. suspend to RAM, hibernation).
  63
  64                 All devices have one of the following two values for the
  65                 power/async file:
  66
  67                 + "enabled\n" to permit the asynchronous suspend/resume;
  68                 + "disabled\n" to forbid it;
  69
  70                 The value of this attribute may be changed by writing either
  71                 "enabled", or "disabled" to it.
  72
  73                 It generally is unsafe to permit the asynchronous suspend/resume
  74                 of a device unless it is certain that all of the PM dependencies
  75                 of the device are known to the PM core.  However, for some
  76                 devices this attribute is set to "enabled" by bus type code or
  77                 device drivers and in that cases it should be safe to leave the
  78                 default value.
  79
  80 What:           /sys/devices/.../power/wakeup_count
  81 Date:           September 2010
  82 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  83 Description:
  84                 The /sys/devices/.../wakeup_count attribute contains the number
  85                 of signaled wakeup events associated with the device.  This
  86                 attribute is read-only.  If the device is not capable to wake up
  87                 the system from sleep states, this attribute is not present.
  88                 If the device is not enabled to wake up the system from sleep
  89                 states, this attribute is empty.
  90
  91 What:           /sys/devices/.../power/wakeup_active_count
  92 Date:           September 2010
  93 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
  94 Description:
  95                 The /sys/devices/.../wakeup_active_count attribute contains the
  96                 number of times the processing of wakeup events associated with
  97                 the device was completed (at the kernel level).  This attribute
  98                 is read-only.  If the device is not capable to wake up the
  99                 system from sleep states, this attribute is not present.  If
 100                 the device is not enabled to wake up the system from sleep
 101                 states, this attribute is empty.
 102
 103 What:           /sys/devices/.../power/wakeup_abort_count
 104 Date:           February 2012
 105 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 106 Description:
 107                 The /sys/devices/.../wakeup_abort_count attribute contains the
 108                 number of times the processing of a wakeup event associated with
 109                 the device might have aborted system transition into a sleep
 110                 state in progress.  This attribute is read-only.  If the device
 111                 is not capable to wake up the system from sleep states, this
 112                 attribute is not present.  If the device is not enabled to wake
 113                 up the system from sleep states, this attribute is empty.
 114
 115 What:           /sys/devices/.../power/wakeup_expire_count
 116 Date:           February 2012
 117 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 118 Description:
 119                 The /sys/devices/.../wakeup_expire_count attribute contains the
 120                 number of times a wakeup event associated with the device has
 121                 been reported with a timeout that expired.  This attribute is
 122                 read-only.  If the device is not capable to wake up the system
 123                 from sleep states, this attribute is not present.  If the
 124                 device is not enabled to wake up the system from sleep states,
 125                 this attribute is empty.
 126
 127 What:           /sys/devices/.../power/wakeup_active
 128 Date:           September 2010
 129 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 130 Description:
 131                 The /sys/devices/.../wakeup_active attribute contains either 1,
 132                 or 0, depending on whether or not a wakeup event associated with
 133                 the device is being processed (1).  This attribute is read-only.
 134                 If the device is not capable to wake up the system from sleep
 135                 states, this attribute is not present.  If the device is not
 136                 enabled to wake up the system from sleep states, this attribute
 137                 is empty.
 138
 139 What:           /sys/devices/.../power/wakeup_total_time_ms
 140 Date:           September 2010
 141 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 142 Description:
 143                 The /sys/devices/.../wakeup_total_time_ms attribute contains
 144                 the total time of processing wakeup events associated with the
 145                 device, in milliseconds.  This attribute is read-only.  If the
 146                 device is not capable to wake up the system from sleep states,
 147                 this attribute is not present.  If the device is not enabled to
 148                 wake up the system from sleep states, this attribute is empty.
 149
 150 What:           /sys/devices/.../power/wakeup_max_time_ms
 151 Date:           September 2010
 152 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 153 Description:
 154                 The /sys/devices/.../wakeup_max_time_ms attribute contains
 155                 the maximum time of processing a single wakeup event associated
 156                 with the device, in milliseconds.  This attribute is read-only.
 157                 If the device is not capable to wake up the system from sleep
 158                 states, this attribute is not present.  If the device is not
 159                 enabled to wake up the system from sleep states, this attribute
 160                 is empty.
 161
 162 What:           /sys/devices/.../power/wakeup_last_time_ms
 163 Date:           September 2010
 164 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 165 Description:
 166                 The /sys/devices/.../wakeup_last_time_ms attribute contains
 167                 the value of the monotonic clock corresponding to the time of
 168                 signaling the last wakeup event associated with the device, in
 169                 milliseconds.  This attribute is read-only.  If the device is
 170                 not enabled to wake up the system from sleep states, this
 171                 attribute is not present.  If the device is not enabled to wake
 172                 up the system from sleep states, this attribute is empty.
 173
 174 What:           /sys/devices/.../power/wakeup_prevent_sleep_time_ms
 175 Date:           February 2012
 176 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 177 Description:
 178                 The /sys/devices/.../wakeup_prevent_sleep_time_ms attribute
 179                 contains the total time the device has been preventing
 180                 opportunistic transitions to sleep states from occurring.
 181                 This attribute is read-only.  If the device is not capable to
 182                 wake up the system from sleep states, this attribute is not
 183                 present.  If the device is not enabled to wake up the system
 184                 from sleep states, this attribute is empty.
 185
 186 What:           /sys/devices/.../power/autosuspend_delay_ms
 187 Date:           September 2010
 188 Contact:        Alan Stern <stern@rowland.harvard.edu>
 189 Description:
 190                 The /sys/devices/.../power/autosuspend_delay_ms attribute
 191                 contains the autosuspend delay value (in milliseconds).  Some
 192                 drivers do not want their device to suspend as soon as it
 193                 becomes idle at run time; they want the device to remain
 194                 inactive for a certain minimum period of time first.  That
 195                 period is called the autosuspend delay.  Negative values will
 196                 prevent the device from being suspended at run time (similar
 197                 to writing "on" to the power/control attribute).  Values >=
 198                 1000 will cause the autosuspend timer expiration to be rounded
 199                 up to the nearest second.
 200
 201                 Not all drivers support this attribute.  If it isn't supported,
 202                 attempts to read or write it will yield I/O errors.
 203
 204 What:           /sys/devices/.../power/pm_qos_resume_latency_us
 205 Date:           March 2012
 206 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 207 Description:
 208                 The /sys/devices/.../power/pm_qos_resume_latency_us attribute
 209                 contains the PM QoS resume latency limit for the given device,
 210                 which is the maximum allowed time it can take to resume the
 211                 device, after it has been suspended at run time, from a resume
 212                 request to the moment the device will be ready to process I/O,
 213                 in microseconds.  If it is equal to 0, however, this means that
 214                 the PM QoS resume latency may be arbitrary.
 215
 216                 Not all drivers support this attribute.  If it isn't supported,
 217                 it is not present.
 218
 219                 This attribute has no effect on system-wide suspend/resume and
 220                 hibernation.
 221
 222 What:           /sys/devices/.../power/pm_qos_latency_tolerance_us
 223 Date:           January 2014
 224 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 225 Description:
 226                 The /sys/devices/.../power/pm_qos_latency_tolerance_us attribute
 227                 contains the PM QoS active state latency tolerance limit for the
 228                 given device in microseconds.  That is the maximum memory access
 229                 latency the device can suffer without any visible adverse
 230                 effects on user space functionality.  If that value is the
 231                 string "any", the latency does not matter to user space at all,
 232                 but hardware should not be allowed to set the latency tolerance
 233                 for the device automatically.
 234
 235                 Reading "auto" from this file means that the maximum memory
 236                 access latency for the device may be determined automatically
 237                 by the hardware as needed.  Writing "auto" to it allows the
 238                 hardware to be switched to this mode if there are no other
 239                 latency tolerance requirements from the kernel side.
 240
 241                 This attribute is only present if the feature controlled by it
 242                 is supported by the hardware.
 243
 244                 This attribute has no effect on runtime suspend and resume of
 245                 devices and on system-wide suspend/resume and hibernation.
 246
 247 What:           /sys/devices/.../power/pm_qos_no_power_off
 248 Date:           September 2012
 249 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 250 Description:
 251                 The /sys/devices/.../power/pm_qos_no_power_off attribute
 252                 is used for manipulating the PM QoS "no power off" flag.  If
 253                 set, this flag indicates to the kernel that power should not
 254                 be removed entirely from the device.
 255
 256                 Not all drivers support this attribute.  If it isn't supported,
 257                 it is not present.
 258
 259                 This attribute has no effect on system-wide suspend/resume and
 260                 hibernation.
 261
 262 What:           /sys/devices/.../power/pm_qos_remote_wakeup
 263 Date:           September 2012
 264 Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
 265 Description:
 266                 The /sys/devices/.../power/pm_qos_remote_wakeup attribute
 267                 is used for manipulating the PM QoS "remote wakeup required"
 268                 flag.  If set, this flag indicates to the kernel that the
 269                 device is a source of user events that have to be signaled from
 270                 its low-power states.
 271
 272                 Not all drivers support this attribute.  If it isn't supported,
 273                 it is not present.
 274
 275                 This attribute has no effect on system-wide suspend/resume and
 276                 hibernation.