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. 41For information on enabling the power cap feature, refer to the description 42of the "force_on_cap" option in the "Module Parameters" chapter. 43To use the power cap feature properly, you need to set appropriate value 44(in microWatts) to the `power[1-*]_cap` sysfs files. 45The value must be within the range between the minimum value at `power[1-]_cap_min` 46and the maximum value at `power[1-]_cap_max (both in microWatts)`. 47 48When the average power consumption exceeds the cap, an ACPI event will be 49broadcast on the netlink event socket and a poll notification will be sent to the 50appropriate `power[1-*]_alarm` file to indicate that capping has begun, and the 51hardware has taken action to reduce power consumption. Most likely this will 52result in reduced performance. 53 54There are a few other ACPI notifications that can be sent by the firmware. In 55all cases the ACPI event will be broadcast on the ACPI netlink event socket as 56well as sent as a poll notification to a sysfs file. The events are as 57follows: 58 59`power[1-*]_cap` will be notified if the firmware changes the power cap. 60`power[1-*]_interval` will be notified if the firmware changes the averaging 61interval. 62 63Module Parameters 64----------------- 65 66* force_cap_on: bool 67 Forcefully enable the power capping feature to specify 68 the upper limit of the system's power consumption. 69 70 By default, the driver's power capping feature is only 71 enabled on IBM products. 72 Therefore, on other systems that support power capping, 73 you will need to use the option to enable it. 74 75 Note: power capping is potentially unsafe feature. 76 Please check the platform specifications to make sure 77 that capping is supported before using this option. 78