Documentation/ABI/testing/sysfs-devices-power

   1 What:           /sys/devices/.../power/
   2 Date:           January 2009
   3 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
   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@sisk.pl>
  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@sisk.pl>
  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@sisk.pl>
  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@sisk.pl>
  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 enabled to wake up
  87                 the system from sleep states, this attribute is not present.
  88
  89 What:           /sys/devices/.../power/wakeup_active_count
  90 Date:           September 2010
  91 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
  92 Description:
  93                 The /sys/devices/.../wakeup_active_count attribute contains the
  94                 number of times the processing of wakeup events associated with
  95                 the device was completed (at the kernel level).  This attribute
  96                 is read-only.  If the device is not enabled to wake up the
  97                 system from sleep states, this attribute is not present.
  98
  99 What:           /sys/devices/.../power/wakeup_abort_count
 100 Date:           February 2012
 101 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
 102 Description:
 103                 The /sys/devices/.../wakeup_abort_count attribute contains the
 104                 number of times the processing of a wakeup event associated with
 105                 the device might have aborted system transition into a sleep
 106                 state in progress.  This attribute is read-only.  If the device
 107                 is not enabled to wake up the system from sleep states, this
 108                 attribute is not present.
 109
 110 What:           /sys/devices/.../power/wakeup_expire_count
 111 Date:           February 2012
 112 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
 113 Description:
 114                 The /sys/devices/.../wakeup_expire_count attribute contains the
 115                 number of times a wakeup event associated with the device has
 116                 been reported with a timeout that expired.  This attribute is
 117                 read-only.  If the device is not enabled to wake up the system
 118                 from sleep states, this attribute is not present.
 119
 120 What:           /sys/devices/.../power/wakeup_active
 121 Date:           September 2010
 122 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
 123 Description:
 124                 The /sys/devices/.../wakeup_active attribute contains either 1,
 125                 or 0, depending on whether or not a wakeup event associated with
 126                 the device is being processed (1).  This attribute is read-only.
 127                 If the device is not enabled to wake up the system from sleep
 128                 states, this attribute is not present.
 129
 130 What:           /sys/devices/.../power/wakeup_total_time_ms
 131 Date:           September 2010
 132 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
 133 Description:
 134                 The /sys/devices/.../wakeup_total_time_ms attribute contains
 135                 the total time of processing wakeup events associated with the
 136                 device, in milliseconds.  This attribute is read-only.  If the
 137                 device is not enabled to wake up the system from sleep states,
 138                 this attribute is not present.
 139
 140 What:           /sys/devices/.../power/wakeup_max_time_ms
 141 Date:           September 2010
 142 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
 143 Description:
 144                 The /sys/devices/.../wakeup_max_time_ms attribute contains
 145                 the maximum time of processing a single wakeup event associated
 146                 with the device, in milliseconds.  This attribute is read-only.
 147                 If the device is not enabled to wake up the system from sleep
 148                 states, this attribute is not present.
 149
 150 What:           /sys/devices/.../power/wakeup_last_time_ms
 151 Date:           September 2010
 152 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
 153 Description:
 154                 The /sys/devices/.../wakeup_last_time_ms attribute contains
 155                 the value of the monotonic clock corresponding to the time of
 156                 signaling the last wakeup event associated with the device, in
 157                 milliseconds.  This attribute is read-only.  If the device is
 158                 not enabled to wake up the system from sleep states, this
 159                 attribute is not present.
 160
 161 What:           /sys/devices/.../power/wakeup_prevent_sleep_time_ms
 162 Date:           February 2012
 163 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
 164 Description:
 165                 The /sys/devices/.../wakeup_prevent_sleep_time_ms attribute
 166                 contains the total time the device has been preventing
 167                 opportunistic transitions to sleep states from occurring.
 168                 This attribute is read-only.  If the device is not enabled to
 169                 wake up the system from sleep states, this attribute is not
 170                 present.
 171
 172 What:           /sys/devices/.../power/autosuspend_delay_ms
 173 Date:           September 2010
 174 Contact:        Alan Stern <stern@rowland.harvard.edu>
 175 Description:
 176                 The /sys/devices/.../power/autosuspend_delay_ms attribute
 177                 contains the autosuspend delay value (in milliseconds).  Some
 178                 drivers do not want their device to suspend as soon as it
 179                 becomes idle at run time; they want the device to remain
 180                 inactive for a certain minimum period of time first.  That
 181                 period is called the autosuspend delay.  Negative values will
 182                 prevent the device from being suspended at run time (similar
 183                 to writing "on" to the power/control attribute).  Values >=
 184                 1000 will cause the autosuspend timer expiration to be rounded
 185                 up to the nearest second.
 186
 187                 Not all drivers support this attribute.  If it isn't supported,
 188                 attempts to read or write it will yield I/O errors.
 189
 190 What:           /sys/devices/.../power/pm_qos_latency_us
 191 Date:           March 2012
 192 Contact:        Rafael J. Wysocki <rjw@sisk.pl>
 193 Description:
 194                 The /sys/devices/.../power/pm_qos_resume_latency_us attribute
 195                 contains the PM QoS resume latency limit for the given device,
 196                 which is the maximum allowed time it can take to resume the
 197                 device, after it has been suspended at run time, from a resume
 198                 request to the moment the device will be ready to process I/O,
 199                 in microseconds.  If it is equal to 0, however, this means that
 200                 the PM QoS resume latency may be arbitrary.
 201
 202                 Not all drivers support this attribute.  If it isn't supported,
 203                 it is not present.
 204
 205                 This attribute has no effect on system-wide suspend/resume and
 206                 hibernation.