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Based on kernel version 3.9. Page generated on 2013-05-02 23:12 EST.

	Debugging hibernation and suspend
		(C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL
	
	1. Testing hibernation (aka suspend to disk or STD)
	
	To check if hibernation works, you can try to hibernate in the "reboot" mode:
	
	# echo reboot > /sys/power/disk
	# echo disk > /sys/power/state
	
	and the system should create a hibernation image, reboot, resume and get back to
	the command prompt where you have started the transition.  If that happens,
	hibernation is most likely to work correctly.  Still, you need to repeat the
	test at least a couple of times in a row for confidence.  [This is necessary,
	because some problems only show up on a second attempt at suspending and
	resuming the system.]  Moreover, hibernating in the "reboot" and "shutdown"
	modes causes the PM core to skip some platform-related callbacks which on ACPI
	systems might be necessary to make hibernation work.  Thus, if your machine fails
	to hibernate or resume in the "reboot" mode, you should try the "platform" mode:
	
	# echo platform > /sys/power/disk
	# echo disk > /sys/power/state
	
	which is the default and recommended mode of hibernation.
	
	Unfortunately, the "platform" mode of hibernation does not work on some systems
	with broken BIOSes.  In such cases the "shutdown" mode of hibernation might
	work:
	
	# echo shutdown > /sys/power/disk
	# echo disk > /sys/power/state
	
	(it is similar to the "reboot" mode, but it requires you to press the power
	button to make the system resume).
	
	If neither "platform" nor "shutdown" hibernation mode works, you will need to
	identify what goes wrong.
	
	a) Test modes of hibernation
	
	To find out why hibernation fails on your system, you can use a special testing
	facility available if the kernel is compiled with CONFIG_PM_DEBUG set.  Then,
	there is the file /sys/power/pm_test that can be used to make the hibernation
	core run in a test mode.  There are 5 test modes available:
	
	freezer
	- test the freezing of processes
	
	devices
	- test the freezing of processes and suspending of devices
	
	platform
	- test the freezing of processes, suspending of devices and platform
	  global control methods(*)
	
	processors
	- test the freezing of processes, suspending of devices, platform
	  global control methods(*) and the disabling of nonboot CPUs
	
	core
	- test the freezing of processes, suspending of devices, platform global
	  control methods(*), the disabling of nonboot CPUs and suspending of
	  platform/system devices
	
	(*) the platform global control methods are only available on ACPI systems
	    and are only tested if the hibernation mode is set to "platform"
	
	To use one of them it is necessary to write the corresponding string to
	/sys/power/pm_test (eg. "devices" to test the freezing of processes and
	suspending devices) and issue the standard hibernation commands.  For example,
	to use the "devices" test mode along with the "platform" mode of hibernation,
	you should do the following:
	
	# echo devices > /sys/power/pm_test
	# echo platform > /sys/power/disk
	# echo disk > /sys/power/state
	
	Then, the kernel will try to freeze processes, suspend devices, wait 5 seconds,
	resume devices and thaw processes.  If "platform" is written to
	/sys/power/pm_test , then after suspending devices the kernel will additionally
	invoke the global control methods (eg. ACPI global control methods) used to
	prepare the platform firmware for hibernation.  Next, it will wait 5 seconds and
	invoke the platform (eg. ACPI) global methods used to cancel hibernation etc.
	
	Writing "none" to /sys/power/pm_test causes the kernel to switch to the normal
	hibernation/suspend operations.  Also, when open for reading, /sys/power/pm_test
	contains a space-separated list of all available tests (including "none" that
	represents the normal functionality) in which the current test level is
	indicated by square brackets.
	
	Generally, as you can see, each test level is more "invasive" than the previous
	one and the "core" level tests the hardware and drivers as deeply as possible
	without creating a hibernation image.  Obviously, if the "devices" test fails,
	the "platform" test will fail as well and so on.  Thus, as a rule of thumb, you
	should try the test modes starting from "freezer", through "devices", "platform"
	and "processors" up to "core" (repeat the test on each level a couple of times
	to make sure that any random factors are avoided).
	
	If the "freezer" test fails, there is a task that cannot be frozen (in that case
	it usually is possible to identify the offending task by analysing the output of
	dmesg obtained after the failing test).  Failure at this level usually means
	that there is a problem with the tasks freezer subsystem that should be
	reported.
	
	If the "devices" test fails, most likely there is a driver that cannot suspend
	or resume its device (in the latter case the system may hang or become unstable
	after the test, so please take that into consideration).  To find this driver,
	you can carry out a binary search according to the rules:
	- if the test fails, unload a half of the drivers currently loaded and repeat
	(that would probably involve rebooting the system, so always note what drivers
	have been loaded before the test),
	- if the test succeeds, load a half of the drivers you have unloaded most
	recently and repeat.
	
	Once you have found the failing driver (there can be more than just one of
	them), you have to unload it every time before hibernation.  In that case please
	make sure to report the problem with the driver.
	
	It is also possible that the "devices" test will still fail after you have
	unloaded all modules. In that case, you may want to look in your kernel
	configuration for the drivers that can be compiled as modules (and test again
	with these drivers compiled as modules).  You may also try to use some special
	kernel command line options such as "noapic", "noacpi" or even "acpi=off".
	
	If the "platform" test fails, there is a problem with the handling of the
	platform (eg. ACPI) firmware on your system.  In that case the "platform" mode
	of hibernation is not likely to work.  You can try the "shutdown" mode, but that
	is rather a poor man's workaround.
	
	If the "processors" test fails, the disabling/enabling of nonboot CPUs does not
	work (of course, this only may be an issue on SMP systems) and the problem
	should be reported.  In that case you can also try to switch the nonboot CPUs
	off and on using the /sys/devices/system/cpu/cpu*/online sysfs attributes and
	see if that works.
	
	If the "core" test fails, which means that suspending of the system/platform
	devices has failed (these devices are suspended on one CPU with interrupts off),
	the problem is most probably hardware-related and serious, so it should be
	reported.
	
	A failure of any of the "platform", "processors" or "core" tests may cause your
	system to hang or become unstable, so please beware.  Such a failure usually
	indicates a serious problem that very well may be related to the hardware, but
	please report it anyway.
	
	b) Testing minimal configuration
	
	If all of the hibernation test modes work, you can boot the system with the
	"init=/bin/bash" command line parameter and attempt to hibernate in the
	"reboot", "shutdown" and "platform" modes.  If that does not work, there
	probably is a problem with a driver statically compiled into the kernel and you
	can try to compile more drivers as modules, so that they can be tested
	individually.  Otherwise, there is a problem with a modular driver and you can
	find it by loading a half of the modules you normally use and binary searching
	in accordance with the algorithm:
	- if there are n modules loaded and the attempt to suspend and resume fails,
	unload n/2 of the modules and try again (that would probably involve rebooting
	the system),
	- if there are n modules loaded and the attempt to suspend and resume succeeds,
	load n/2 modules more and try again.
	
	Again, if you find the offending module(s), it(they) must be unloaded every time
	before hibernation, and please report the problem with it(them).
	
	c) Advanced debugging
	
	In case that hibernation does not work on your system even in the minimal
	configuration and compiling more drivers as modules is not practical or some
	modules cannot be unloaded, you can use one of the more advanced debugging
	techniques to find the problem.  First, if there is a serial port in your box,
	you can boot the kernel with the 'no_console_suspend' parameter and try to log
	kernel messages using the serial console.  This may provide you with some
	information about the reasons of the suspend (resume) failure.  Alternatively,
	it may be possible to use a FireWire port for debugging with firescope
	(ftp://ftp.firstfloor.org/pub/ak/firescope/).  On x86 it is also possible to
	use the PM_TRACE mechanism documented in Documentation/power/s2ram.txt .
	
	2. Testing suspend to RAM (STR)
	
	To verify that the STR works, it is generally more convenient to use the s2ram
	tool available from http://suspend.sf.net and documented at
	http://en.opensuse.org/SDB:Suspend_to_RAM.
	
	Namely, after writing "freezer", "devices", "platform", "processors", or "core"
	into /sys/power/pm_test (available if the kernel is compiled with
	CONFIG_PM_DEBUG set) the suspend code will work in the test mode corresponding
	to given string.  The STR test modes are defined in the same way as for
	hibernation, so please refer to Section 1 for more information about them.  In
	particular, the "core" test allows you to test everything except for the actual
	invocation of the platform firmware in order to put the system into the sleep
	state.
	
	Among other things, the testing with the help of /sys/power/pm_test may allow
	you to identify drivers that fail to suspend or resume their devices.  They
	should be unloaded every time before an STR transition.
	
	Next, you can follow the instructions at http://en.opensuse.org/s2ram to test
	the system, but if it does not work "out of the box", you may need to boot it
	with "init=/bin/bash" and test s2ram in the minimal configuration.  In that
	case, you may be able to search for failing drivers by following the procedure
	analogous to the one described in section 1.  If you find some failing drivers,
	you will have to unload them every time before an STR transition (ie. before
	you run s2ram), and please report the problems with them.
	
	There is a debugfs entry which shows the suspend to RAM statistics. Here is an
	example of its output.
		# mount -t debugfs none /sys/kernel/debug
		# cat /sys/kernel/debug/suspend_stats
		success: 20
		fail: 5
		failed_freeze: 0
		failed_prepare: 0
		failed_suspend: 5
		failed_suspend_noirq: 0
		failed_resume: 0
		failed_resume_noirq: 0
		failures:
		  last_failed_dev:	alarm
					adc
		  last_failed_errno:	-16
					-16
		  last_failed_step:	suspend
					suspend
	Field success means the success number of suspend to RAM, and field fail means
	the failure number. Others are the failure number of different steps of suspend
	to RAM. suspend_stats just lists the last 2 failed devices, error number and
	failed step of suspend.

• [ power ]
• 00-INDEX
• apm-acpi.txt
• basic-pm-debugging.txt
• charger-manager.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
•