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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. |