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Diffstat (limited to 'Documentation/power/basic-pm-debugging.txt')
| -rw-r--r-- | Documentation/power/basic-pm-debugging.txt | 216 |
1 files changed, 157 insertions, 59 deletions
diff --git a/Documentation/power/basic-pm-debugging.txt b/Documentation/power/basic-pm-debugging.txt index 57aef2f..1555001 100644 --- a/Documentation/power/basic-pm-debugging.txt +++ b/Documentation/power/basic-pm-debugging.txt @@ -1,45 +1,111 @@ -Debugging suspend and resume +Debugging hibernation and suspend (C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, 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 -or +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 -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: + +freezer +- test the freezing of processes + +devices +- test the freezing of processes and suspending of devices -a) Test mode of STD +platform +- 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: +processors +- test the freezing of processes, suspending of devices, platform + global control methods(*) and the disabling of nonboot CPUs -# echo test > /sys/power/disk +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 -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 +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), @@ -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 +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 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 the system), @@ -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 +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. |
