linux/Documentation/ABI/testing/sysfs-devices-power_state

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What: /sys/devices/.../power_state
Date: January 2013
Contact: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Description:
The /sys/devices/.../power_state attribute is only present for
device objects representing ACPI device nodes that provide power
management methods.
If present, it contains a string representing the current ACPI
power state of the given device node. Its possible values,
"D0", "D1", "D2", "D3hot", and "D3cold", reflect the power state
names defined by the ACPI specification (ACPI 4 and above).
If the device node uses shared ACPI power resources, this state
determines a list of power resources required not to be turned
off. However, some power resources needed by the device node in
higher-power (lower-number) states may also be ON because of
some other devices using them at the moment.
This attribute is read-only.