linux/Documentation/hwmon/acpi_power_meter
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   1Kernel driver power_meter
   2=========================
   3
   4This driver talks to ACPI 4.0 power meters.
   5
   6Supported systems:
   7  * Any recent system with ACPI 4.0.
   8    Prefix: 'power_meter'
   9    Datasheet: http://acpi.info/, section 10.4.
  10
  11Author: Darrick J. Wong
  12
  13Description
  14-----------
  15
  16This driver implements sensor reading support for the power meters exposed in
  17the ACPI 4.0 spec (Chapter 10.4).  These devices have a simple set of
  18features--a power meter that returns average power use over a configurable
  19interval, an optional capping mechanism, and a couple of trip points.  The
  20sysfs interface conforms with the specification outlined in the "Power" section
  21of Documentation/hwmon/sysfs-interface.
  22
  23Special Features
  24----------------
  25
  26The power[1-*]_is_battery knob indicates if the power supply is a battery.
  27Both power[1-*]_average_{min,max} must be set before the trip points will work.
  28When both of them are set, an ACPI event will be broadcast on the ACPI netlink
  29socket and a poll notification will be sent to the appropriate
  30power[1-*]_average sysfs file.
  31
  32The power[1-*]_{model_number, serial_number, oem_info} fields display arbitrary
  33strings that ACPI provides with the meter.  The measures/ directory contains
  34symlinks to the devices that this meter measures.
  35
  36Some computers have the ability to enforce a power cap in hardware.  If this is
  37the case, the power[1-*]_cap and related sysfs files will appear.  When the
  38average power consumption exceeds the cap, an ACPI event will be broadcast on
  39the netlink event socket and a poll notification will be sent to the
  40appropriate power[1-*]_alarm file to indicate that capping has begun, and the
  41hardware has taken action to reduce power consumption.  Most likely this will
  42result in reduced performance.
  43
  44There are a few other ACPI notifications that can be sent by the firmware.  In
  45all cases the ACPI event will be broadcast on the ACPI netlink event socket as
  46well as sent as a poll notification to a sysfs file.  The events are as
  47follows:
  48
  49power[1-*]_cap will be notified if the firmware changes the power cap.
  50power[1-*]_interval will be notified if the firmware changes the averaging
  51interval.
  52
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