hwmon driver for ACPI 4.0 power meters

This driver exposes ACPI 4.0 compliant power meters as hardware monitoring
devices.  This second revision of the driver also exports the ACPI string
info as sysfs attributes, a list of the devices that the meter measures,
and will send ACPI notifications over the ACPI netlink socket.  This
latest revision only enables the power capping controls if it can be
confirmed that the power cap can be enforced by the hardware and explains
how the notification interfaces work.

[akpm@linux-foundation.org: remove default-y]
[akpm@linux-foundation.org: build fix]
Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/Documentation/hwmon/acpi_power_meter b/Documentation/hwmon/acpi_power_meter
new file mode 100644
index 000000000000..c80399a00c50
--- /dev/null
+++ b/Documentation/hwmon/acpi_power_meter
@@ -0,0 +1,51 @@
+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.