Documentation / power / interface.txt

Custom Search

Based on kernel version 3.2. Page generated on 2012-01-05 23:29 EST.

	Power Management Interface
	
	
	The power management subsystem provides a unified sysfs interface to 
	userspace, regardless of what architecture or platform one is
	running. The interface exists in /sys/power/ directory (assuming sysfs
	is mounted at /sys). 
	
	/sys/power/state controls system power state. Reading from this file
	returns what states are supported, which is hard-coded to 'standby'
	(Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk'
	(Suspend-to-Disk). 
	
	Writing to this file one of those strings causes the system to
	transition into that state. Please see the file
	Documentation/power/states.txt for a description of each of those
	states.
	
	
	/sys/power/disk controls the operating mode of the suspend-to-disk
	mechanism. Suspend-to-disk can be handled in several ways. We have a
	few options for putting the system to sleep - using the platform driver
	(e.g. ACPI or other suspend_ops), powering off the system or rebooting the
	system (for testing).
	
	Additionally, /sys/power/disk can be used to turn on one of the two testing
	modes of the suspend-to-disk mechanism: 'testproc' or 'test'.  If the
	suspend-to-disk mechanism is in the 'testproc' mode, writing 'disk' to
	/sys/power/state will cause the kernel to disable nonboot CPUs and freeze
	tasks, wait for 5 seconds, unfreeze tasks and enable nonboot CPUs.  If it is
	in the 'test' mode, writing 'disk' to /sys/power/state will cause the kernel
	to disable nonboot CPUs and freeze tasks, shrink memory, suspend devices, wait
	for 5 seconds, resume devices, unfreeze tasks and enable nonboot CPUs.  Then,
	we are able to look in the log messages and work out, for example, which code
	is being slow and which device drivers are misbehaving.
	
	Reading from this file will display all supported modes and the currently
	selected one in brackets, for example
	
		[shutdown] reboot test testproc
	
	Writing to this file will accept one of
	
	       'platform' (only if the platform supports it)
	       'shutdown'
	       'reboot'
	       'testproc'
	       'test'
	
	/sys/power/image_size controls the size of the image created by
	the suspend-to-disk mechanism.  It can be written a string
	representing a non-negative integer that will be used as an upper
	limit of the image size, in bytes.  The suspend-to-disk mechanism will
	do its best to ensure the image size will not exceed that number.  However,
	if this turns out to be impossible, it will try to suspend anyway using the
	smallest image possible.  In particular, if "0" is written to this file, the
	suspend image will be as small as possible.
	
	Reading from this file will display the current image size limit, which
	is set to 2/5 of available RAM by default.
	
	/sys/power/pm_trace controls the code which saves the last PM event point in
	the RTC across reboots, so that you can debug a machine that just hangs
	during suspend (or more commonly, during resume).  Namely, the RTC is only
	used to save the last PM event point if this file contains '1'.  Initially it
	contains '0' which may be changed to '1' by writing a string representing a
	nonzero integer into it.
	
	To use this debugging feature you should attempt to suspend the machine, then
	reboot it and run
	
		dmesg -s 1000000 | grep 'hash matches'
	
	CAUTION: Using it will cause your machine's real-time (CMOS) clock to be
	set to a random invalid time after a resume.

• [ power ]
• 00-INDEX
• apm-acpi.txt
• basic-pm-debugging.txt
• devices.txt
• drivers-testing.txt
• freezing-of-tasks.txt
• interface.txt
• notifiers.txt
• opp.txt
• pci.txt
• pm_qos_interface.txt
• power_supply_class.txt
• [ regulator ]
• runtime_pm.txt
• s2ram.txt
• states.txt
• suspend-and-cpuhotplug.txt
• swsusp-and-swap-files.txt
• swsusp-dmcrypt.txt
• swsusp.txt
• tricks.txt
• userland-swsusp.txt
• video.txt
• video_extension.txt
•