xref: /openbmc/linux/Documentation/ABI/testing/sysfs-devices-power (revision 5a2eb858)

What:		/sys/devices/.../power/
Date:		January 2009
Contact:	Rafael J. Wysocki <rjw@sisk.pl>
Description:
		The /sys/devices/.../power directory contains attributes
		allowing the user space to check and modify some power
		management related properties of given device.

What:		/sys/devices/.../power/wakeup
Date:		January 2009
Contact:	Rafael J. Wysocki <rjw@sisk.pl>
Description:
		The /sys/devices/.../power/wakeup attribute allows the user
		space to check if the device is enabled to wake up the system
		from sleep states, such as the memory sleep state (suspend to
		RAM) and hibernation (suspend to disk), and to enable or disable
		it to do that as desired.

		Some devices support "wakeup" events, which are hardware signals
		used to activate the system from a sleep state.  Such devices
		have one of the following two values for the sysfs power/wakeup
		file:

		+ "enabled\n" to issue the events;
		+ "disabled\n" not to do so;

		In that cases the user space can change the setting represented
		by the contents of this file by writing either "enabled", or
		"disabled" to it.

		For the devices that are not capable of generating system wakeup
		events this file contains "\n".  In that cases the user space
		cannot modify the contents of this file and the device cannot be
		enabled to wake up the system.

What:		/sys/devices/.../power/control
Date:		January 2009
Contact:	Rafael J. Wysocki <rjw@sisk.pl>
Description:
		The /sys/devices/.../power/control attribute allows the user
		space to control the run-time power management of the device.

		All devices have one of the following two values for the
		power/control file:

		+ "auto\n" to allow the device to be power managed at run time;
		+ "on\n" to prevent the device from being power managed;

		The default for all devices is "auto", which means that they may
		be subject to automatic power management, depending on their
		drivers.  Changing this attribute to "on" prevents the driver
		from power managing the device at run time.  Doing that while
		the device is suspended causes it to be woken up.

What:		/sys/devices/.../power/async
Date:		January 2009
Contact:	Rafael J. Wysocki <rjw@sisk.pl>
Description:
		The /sys/devices/.../async attribute allows the user space to
		enable or diasble the device's suspend and resume callbacks to
		be executed asynchronously (ie. in separate threads, in parallel
		with the main suspend/resume thread) during system-wide power
		transitions (eg. suspend to RAM, hibernation).

		All devices have one of the following two values for the
		power/async file:

		+ "enabled\n" to permit the asynchronous suspend/resume;
		+ "disabled\n" to forbid it;

		The value of this attribute may be changed by writing either
		"enabled", or "disabled" to it.

		It generally is unsafe to permit the asynchronous suspend/resume
		of a device unless it is certain that all of the PM dependencies
		of the device are known to the PM core.  However, for some
		devices this attribute is set to "enabled" by bus type code or
		device drivers and in that cases it should be safe to leave the
		default value.