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Diffstat (limited to 'Documentation/hwmon/acpi_power_meter.rst')
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diff --git a/Documentation/hwmon/acpi_power_meter.rst b/Documentation/hwmon/acpi_power_meter.rst new file mode 100644 index 000000000000..a91403a2a26f --- /dev/null +++ b/Documentation/hwmon/acpi_power_meter.rst @@ -0,0 +1,77 @@ +Kernel driver power_meter +========================= + +This driver talks to ACPI 4.0 power meters. + +Supported systems: + + * Any recent system with ACPI 4.0. + + Prefix: 'power_meter' + + Datasheet: https://uefi.org/specifications, section 10.4. + +Author: Darrick J. Wong + +Description +----------- + +This driver implements sensor reading support for the power meters exposed in +the ACPI 4.0 spec (Chapter 10.4). These devices have a simple set of +features--a power meter that returns average power use over a configurable +interval, an optional capping mechanism, and a couple of trip points. The +sysfs interface conforms with the specification outlined in the "Power" section +of Documentation/hwmon/sysfs-interface.rst. + +Special Features +---------------- + +The `power[1-*]_is_battery` knob indicates if the power supply is a battery. +Both `power[1-*]_average_{min,max}` must be set before the trip points will work. +When both of them are set, an ACPI event will be broadcast on the ACPI netlink +socket and a poll notification will be sent to the appropriate +`power[1-*]_average` sysfs file. + +The `power[1-*]_{model_number, serial_number, oem_info}` fields display +arbitrary strings that ACPI provides with the meter. The measures/ directory +contains symlinks to the devices that this meter measures. + +Some computers have the ability to enforce a power cap in hardware. If this is +the case, the `power[1-*]_cap` and related sysfs files will appear. +For information on enabling the power cap feature, refer to the description +of the "force_on_cap" option in the "Module Parameters" chapter. +To use the power cap feature properly, you need to set appropriate value +(in microWatts) to the `power[1-*]_cap` sysfs files. +The value must be within the range between the minimum value at `power[1-]_cap_min` +and the maximum value at `power[1-]_cap_max (both in microWatts)`. + +When the average power consumption exceeds the cap, an ACPI event will be +broadcast on the netlink event socket and a poll notification will be sent to the +appropriate `power[1-*]_alarm` file to indicate that capping has begun, and the +hardware has taken action to reduce power consumption. Most likely this will +result in reduced performance. + +There are a few other ACPI notifications that can be sent by the firmware. In +all cases the ACPI event will be broadcast on the ACPI netlink event socket as +well as sent as a poll notification to a sysfs file. The events are as +follows: + +`power[1-*]_cap` will be notified if the firmware changes the power cap. +`power[1-*]_interval` will be notified if the firmware changes the averaging +interval. + +Module Parameters +----------------- + +* force_cap_on: bool + Forcefully enable the power capping feature to specify + the upper limit of the system's power consumption. + + By default, the driver's power capping feature is only + enabled on IBM products. + Therefore, on other systems that support power capping, + you will need to use the option to enable it. + + Note: power capping is potentially unsafe feature. + Please check the platform specifications to make sure + that capping is supported before using this option. |