[net-next-2.6.git] / Documentation / hwmon / acpi_power_meter

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: http://acpi.info/, 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.

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.  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.
Commit	Line	Data
de584afa DW	1	Kernel driver power_meter
	2	=========================
	3
	4	This driver talks to ACPI 4.0 power meters.
	5
	6	Supported systems:
	7	* Any recent system with ACPI 4.0.
	8	Prefix: 'power_meter'
	9	Datasheet: http://acpi.info/, section 10.4.
	10
	11	Author: Darrick J. Wong
	12
	13	Description
	14	-----------
	15
	16	This driver implements sensor reading support for the power meters exposed in
	17	the ACPI 4.0 spec (Chapter 10.4). These devices have a simple set of
	18	features--a power meter that returns average power use over a configurable
	19	interval, an optional capping mechanism, and a couple of trip points. The
	20	sysfs interface conforms with the specification outlined in the "Power" section
	21	of Documentation/hwmon/sysfs-interface.
	22
	23	Special Features
	24	----------------
	25
	26	The power[1-*]_is_battery knob indicates if the power supply is a battery.
	27	Both power[1-*]_average_{min,max} must be set before the trip points will work.
	28	When both of them are set, an ACPI event will be broadcast on the ACPI netlink
	29	socket and a poll notification will be sent to the appropriate
	30	power[1-*]_average sysfs file.
	31
	32	The power[1-*]_{model_number, serial_number, oem_info} fields display arbitrary
	33	strings that ACPI provides with the meter. The measures/ directory contains
	34	symlinks to the devices that this meter measures.
	35
	36	Some computers have the ability to enforce a power cap in hardware. If this is
	37	the case, the power[1-*]_cap and related sysfs files will appear. When the
	38	average power consumption exceeds the cap, an ACPI event will be broadcast on
	39	the netlink event socket and a poll notification will be sent to the
	40	appropriate power[1-*]_alarm file to indicate that capping has begun, and the
	41	hardware has taken action to reduce power consumption. Most likely this will
	42	result in reduced performance.
	43
	44	There are a few other ACPI notifications that can be sent by the firmware. In
	45	all cases the ACPI event will be broadcast on the ACPI netlink event socket as
	46	well as sent as a poll notification to a sysfs file. The events are as
	47	follows:
	48
	49	power[1-*]_cap will be notified if the firmware changes the power cap.
	50	power[1-*]_interval will be notified if the firmware changes the averaging
	51	interval.