1Kernel driver power_meter 2========================= 3 4This driver talks to ACPI 4.0 power meters. 5 6Supported systems: 7 8 * Any recent system with ACPI 4.0. 9 10 Prefix: 'power_meter' 11 12 Datasheet: https://uefi.org/specifications, section 10.4. 13 14Author: Darrick J. Wong 15 16Description 17----------- 18 19This driver implements sensor reading support for the power meters exposed in 20the ACPI 4.0 spec (Chapter 10.4). These devices have a simple set of 21features--a power meter that returns average power use over a configurable 22interval, an optional capping mechanism, and a couple of trip points. The 23sysfs interface conforms with the specification outlined in the "Power" section 24of Documentation/hwmon/sysfs-interface.rst. 25 26Special Features 27---------------- 28 29The `power[1-*]_is_battery` knob indicates if the power supply is a battery. 30Both `power[1-*]_average_{min,max}` must be set before the trip points will work. 31When both of them are set, an ACPI event will be broadcast on the ACPI netlink 32socket and a poll notification will be sent to the appropriate 33`power[1-*]_average` sysfs file. 34 35The `power[1-*]_{model_number, serial_number, oem_info}` fields display 36arbitrary strings that ACPI provides with the meter. The measures/ directory 37contains symlinks to the devices that this meter measures. 38 39Some computers have the ability to enforce a power cap in hardware. If this is 40the case, the `power[1-*]_cap` and related sysfs files will appear. When the 41average power consumption exceeds the cap, an ACPI event will be broadcast on 42the netlink event socket and a poll notification will be sent to the 43appropriate `power[1-*]_alarm` file to indicate that capping has begun, and the 44hardware has taken action to reduce power consumption. Most likely this will 45result in reduced performance. 46 47There are a few other ACPI notifications that can be sent by the firmware. In 48all cases the ACPI event will be broadcast on the ACPI netlink event socket as 49well as sent as a poll notification to a sysfs file. The events are as 50follows: 51 52`power[1-*]_cap` will be notified if the firmware changes the power cap. 53`power[1-*]_interval` will be notified if the firmware changes the averaging 54interval. 55