ACPI / PM: Expose power states of ACPI devices to user space

Make it possible to retrieve the current power state of a device with
ACPI power management from user space via sysfs by adding two new
attributes, power_state and real_power_state, to the sysfs directory
associated with the struct acpi_device object representing the
device's ACPI node.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-real_power_state b/Documentation/ABI/testing/sysfs-devices-real_power_state
new file mode 100644
index 000000000000..8b3527c82a7d
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-real_power_state
@@ -0,0 +1,23 @@
+What:           /sys/devices/.../real_power_state
+Date:           January 2013
+Contact:        Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+Description:
+                The /sys/devices/.../real_power_state attribute is only present
+                for device objects representing ACPI device nodes that provide
+                power management methods and use ACPI power resources for power
+                management.
+
+                If present, it contains a string representing the real ACPI
+                power state of the given device node as returned by the _PSC
+                control method or inferred from the configuration of power
+                resources.  Its possible values, "D0", "D1", "D2", "D3hot", and
+                "D3cold", reflect the power state names defined by the ACPI
+                specification (ACPI 4 and above).
+
+                In some situations the value of this attribute may be different
+                from the value of the /sys/devices/.../power_state attribute for
+                the same device object.  If that happens, some shared power
+                resources used by the device node are only ON because of some
+                other devices using them at the moment.
+
+                This attribute is read-only.