|author||Rafael J. Wysocki <email@example.com>||2007-11-19 23:43:34 +0100|
|committer||Len Brown <firstname.lastname@example.org>||2008-02-01 18:30:54 -0500|
PM: Suspend/hibernation debug documentation update (rev. 2)
Update the suspend/hibernation debugging and testing documentation to describe the newly introduced testing facilities. Signed-off-by: Rafael J. Wysocki <email@example.com> Acked-by: Pavel Machek <firstname.lastname@example.org> Signed-off-by: Len Brown <email@example.com>
Diffstat (limited to 'Documentation/power/basic-pm-debugging.txt')
1 files changed, 157 insertions, 59 deletions
diff --git a/Documentation/power/basic-pm-debugging.txt b/Documentation/power/basic-pm-debugging.txt
index 57aef2f6e0de..1555001bc733 100644
@@ -1,45 +1,111 @@
-Debugging suspend and resume
+Debugging hibernation and suspend
(C) 2007 Rafael J. Wysocki <firstname.lastname@example.org>, GPL
-1. Testing suspend to disk (STD)
+1. Testing hibernation (aka suspend to disk or STD)
-To verify that the STD works, you can try to suspend in the "reboot" mode:
+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 suspend, reboot, resume and get back to the command prompt
-where you have started the transition. If that happens, the STD is most likely
-to work correctly, but 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. You should also test
-the "platform" and "shutdown" modes of suspend:
+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 you 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
# echo shutdown > /sys/power/disk
# echo disk > /sys/power/state
-in which cases you will have to press the power button to make the system
-resume. If that does not work, you will need to identify what goes wrong.
+(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:
+- test the freezing of processes
+- test the freezing of processes and suspending of devices
-a) Test mode of STD
+- test the freezing of processes, suspending of devices and platform
+ global control methods(*)
-To verify if there are any drivers that cause problems you can run the STD
-in the test mode:
+- test the freezing of processes, suspending of devices, platform
+ global control methods(*) and the disabling of nonboot CPUs
-# echo test > /sys/power/disk
+- 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
-in which case the system should freeze tasks, suspend devices, disable nonboot
-CPUs (if any), wait for 5 seconds, enable nonboot CPUs, resume devices, thaw
-tasks and return to your command prompt. If that fails, most likely there is
-a driver that fails to either suspend or resume (in the latter case the system
-may hang or be 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:
+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
+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),
@@ -47,23 +113,46 @@ have been loaded before the test),
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 the STD transition. In that case
-please make sure to report the problem with the driver.
-It is also possible that a cycle can still fail after you have unloaded
-all modules. In that case, you would want to look in your kernel configuration
-for the drivers that can be compiled as modules (testing again with them as
-modules), and possibly also try boot time options such as "noapic" or "noacpi".
+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
+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 the test mode of STD works, you can boot the system with "init=/bin/bash"
-and attempt to suspend 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 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
@@ -71,19 +160,19 @@ the system),
load n/2 modules more and try again.
Again, if you find the offending module(s), it(they) must be unloaded every time
-before the STD transition, and please report the problem with it(them).
+before hibernation, and please report the problem with it(them).
c) Advanced debugging
-In case the STD 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 i386 it is also possible to
+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/s2ram.txt .
2. Testing suspend to RAM (STR)
@@ -91,16 +180,25 @@ use the PM_TRACE mechanism documented in Documentation/s2ram.txt .
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/s2ram . However, before doing that it is recommended to
-carry out the procedure described in section 1.
-Assume you have resolved the problems with the STD and you have found some
-failing drivers. These drivers are also likely to fail during the STR or
-during the resume, so it is better to unload them every time before the STR
-transition. Now, 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
-1b). If you find some failing drivers, you will have to unload them every time
-before the STR transition (ie. before you run s2ram), and please report the
-problems with them.
+carry out STR testing using the facility described in section 1.
+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
+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.