acpi_power_meter.rst 2.1 KB

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