1Debugging hibernation and suspend 2 (C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL 3 41. Testing hibernation (aka suspend to disk or STD) 5 6To check if hibernation works, you can try to hibernate in the "reboot" mode: 7 8# echo reboot > /sys/power/disk 9# echo disk > /sys/power/state 10 11and the system should create a hibernation image, reboot, resume and get back to 12the command prompt where you have started the transition. If that happens, 13hibernation is most likely to work correctly. Still, you need to repeat the 14test at least a couple of times in a row for confidence. [This is necessary, 15because some problems only show up on a second attempt at suspending and 16resuming the system.] Moreover, hibernating in the "reboot" and "shutdown" 17modes causes the PM core to skip some platform-related callbacks which on ACPI 18systems might be necessary to make hibernation work. Thus, if your machine fails 19to hibernate or resume in the "reboot" mode, you should try the "platform" mode: 20 21# echo platform > /sys/power/disk 22# echo disk > /sys/power/state 23 24which is the default and recommended mode of hibernation. 25 26Unfortunately, the "platform" mode of hibernation does not work on some systems 27with broken BIOSes. In such cases the "shutdown" mode of hibernation might 28work: 29 30# echo shutdown > /sys/power/disk 31# echo disk > /sys/power/state 32 33(it is similar to the "reboot" mode, but it requires you to press the power 34button to make the system resume). 35 36If neither "platform" nor "shutdown" hibernation mode works, you will need to 37identify what goes wrong. 38 39a) Test modes of hibernation 40 41To find out why hibernation fails on your system, you can use a special testing 42facility available if the kernel is compiled with CONFIG_PM_DEBUG set. Then, 43there is the file /sys/power/pm_test that can be used to make the hibernation 44core run in a test mode. There are 5 test modes available: 45 46freezer 47- test the freezing of processes 48 49devices 50- test the freezing of processes and suspending of devices 51 52platform 53- test the freezing of processes, suspending of devices and platform 54 global control methods(*) 55 56processors 57- test the freezing of processes, suspending of devices, platform 58 global control methods(*) and the disabling of nonboot CPUs 59 60core 61- test the freezing of processes, suspending of devices, platform global 62 control methods(*), the disabling of nonboot CPUs and suspending of 63 platform/system devices 64 65(*) the platform global control methods are only available on ACPI systems 66 and are only tested if the hibernation mode is set to "platform" 67 68To use one of them it is necessary to write the corresponding string to 69/sys/power/pm_test (eg. "devices" to test the freezing of processes and 70suspending devices) and issue the standard hibernation commands. For example, 71to use the "devices" test mode along with the "platform" mode of hibernation, 72you should do the following: 73 74# echo devices > /sys/power/pm_test 75# echo platform > /sys/power/disk 76# echo disk > /sys/power/state 77 78Then, the kernel will try to freeze processes, suspend devices, wait 5 seconds, 79resume devices and thaw processes. If "platform" is written to 80/sys/power/pm_test , then after suspending devices the kernel will additionally 81invoke the global control methods (eg. ACPI global control methods) used to 82prepare the platform firmware for hibernation. Next, it will wait 5 seconds and 83invoke the platform (eg. ACPI) global methods used to cancel hibernation etc. 84 85Writing "none" to /sys/power/pm_test causes the kernel to switch to the normal 86hibernation/suspend operations. Also, when open for reading, /sys/power/pm_test 87contains a space-separated list of all available tests (including "none" that 88represents the normal functionality) in which the current test level is 89indicated by square brackets. 90 91Generally, as you can see, each test level is more "invasive" than the previous 92one and the "core" level tests the hardware and drivers as deeply as possible 93without creating a hibernation image. Obviously, if the "devices" test fails, 94the "platform" test will fail as well and so on. Thus, as a rule of thumb, you 95should try the test modes starting from "freezer", through "devices", "platform" 96and "processors" up to "core" (repeat the test on each level a couple of times 97to make sure that any random factors are avoided). 98 99If the "freezer" test fails, there is a task that cannot be frozen (in that case 100it usually is possible to identify the offending task by analysing the output of 101dmesg obtained after the failing test). Failure at this level usually means 102that there is a problem with the tasks freezer subsystem that should be 103reported. 104 105If the "devices" test fails, most likely there is a driver that cannot suspend 106or resume its device (in the latter case the system may hang or become unstable 107after the test, so please take that into consideration). To find this driver, 108you can carry out a binary search according to the rules: 109- if the test fails, unload a half of the drivers currently loaded and repeat 110(that would probably involve rebooting the system, so always note what drivers 111have been loaded before the test), 112- if the test succeeds, load a half of the drivers you have unloaded most 113recently and repeat. 114 115Once you have found the failing driver (there can be more than just one of 116them), you have to unload it every time before hibernation. In that case please 117make sure to report the problem with the driver. 118 119It is also possible that the "devices" test will still fail after you have 120unloaded all modules. In that case, you may want to look in your kernel 121configuration for the drivers that can be compiled as modules (and test again 122with these drivers compiled as modules). You may also try to use some special 123kernel command line options such as "noapic", "noacpi" or even "acpi=off". 124 125If the "platform" test fails, there is a problem with the handling of the 126platform (eg. ACPI) firmware on your system. In that case the "platform" mode 127of hibernation is not likely to work. You can try the "shutdown" mode, but that 128is rather a poor man's workaround. 129 130If the "processors" test fails, the disabling/enabling of nonboot CPUs does not 131work (of course, this only may be an issue on SMP systems) and the problem 132should be reported. In that case you can also try to switch the nonboot CPUs 133off and on using the /sys/devices/system/cpu/cpu*/online sysfs attributes and 134see if that works. 135 136If the "core" test fails, which means that suspending of the system/platform 137devices has failed (these devices are suspended on one CPU with interrupts off), 138the problem is most probably hardware-related and serious, so it should be 139reported. 140 141A failure of any of the "platform", "processors" or "core" tests may cause your 142system to hang or become unstable, so please beware. Such a failure usually 143indicates a serious problem that very well may be related to the hardware, but 144please report it anyway. 145 146b) Testing minimal configuration 147 148If all of the hibernation test modes work, you can boot the system with the 149"init=/bin/bash" command line parameter and attempt to hibernate in the 150"reboot", "shutdown" and "platform" modes. If that does not work, there 151probably is a problem with a driver statically compiled into the kernel and you 152can try to compile more drivers as modules, so that they can be tested 153individually. Otherwise, there is a problem with a modular driver and you can 154find it by loading a half of the modules you normally use and binary searching 155in accordance with the algorithm: 156- if there are n modules loaded and the attempt to suspend and resume fails, 157unload n/2 of the modules and try again (that would probably involve rebooting 158the system), 159- if there are n modules loaded and the attempt to suspend and resume succeeds, 160load n/2 modules more and try again. 161 162Again, if you find the offending module(s), it(they) must be unloaded every time 163before hibernation, and please report the problem with it(them). 164 165c) Advanced debugging 166 167In case that hibernation does not work on your system even in the minimal 168configuration and compiling more drivers as modules is not practical or some 169modules cannot be unloaded, you can use one of the more advanced debugging 170techniques to find the problem. First, if there is a serial port in your box, 171you can boot the kernel with the 'no_console_suspend' parameter and try to log 172kernel messages using the serial console. This may provide you with some 173information about the reasons of the suspend (resume) failure. Alternatively, 174it may be possible to use a FireWire port for debugging with firescope 175(ftp://ftp.firstfloor.org/pub/ak/firescope/). On x86 it is also possible to 176use the PM_TRACE mechanism documented in Documentation/power/s2ram.txt . 177 1782. Testing suspend to RAM (STR) 179 180To verify that the STR works, it is generally more convenient to use the s2ram 181tool available from http://suspend.sf.net and documented at 182http://en.opensuse.org/SDB:Suspend_to_RAM. 183 184Namely, after writing "freezer", "devices", "platform", "processors", or "core" 185into /sys/power/pm_test (available if the kernel is compiled with 186CONFIG_PM_DEBUG set) the suspend code will work in the test mode corresponding 187to given string. The STR test modes are defined in the same way as for 188hibernation, so please refer to Section 1 for more information about them. In 189particular, the "core" test allows you to test everything except for the actual 190invocation of the platform firmware in order to put the system into the sleep 191state. 192 193Among other things, the testing with the help of /sys/power/pm_test may allow 194you to identify drivers that fail to suspend or resume their devices. They 195should be unloaded every time before an STR transition. 196 197Next, you can follow the instructions at http://en.opensuse.org/s2ram to test 198the system, but if it does not work "out of the box", you may need to boot it 199with "init=/bin/bash" and test s2ram in the minimal configuration. In that 200case, you may be able to search for failing drivers by following the procedure 201analogous to the one described in section 1. If you find some failing drivers, 202you will have to unload them every time before an STR transition (ie. before 203you run s2ram), and please report the problems with them. 204 205There is a debugfs entry which shows the suspend to RAM statistics. Here is an 206example of its output. 207 # mount -t debugfs none /sys/kernel/debug 208 # cat /sys/kernel/debug/suspend_stats 209 success: 20 210 fail: 5 211 failed_freeze: 0 212 failed_prepare: 0 213 failed_suspend: 5 214 failed_suspend_noirq: 0 215 failed_resume: 0 216 failed_resume_noirq: 0 217 failures: 218 last_failed_dev: alarm 219 adc 220 last_failed_errno: -16 221 -16 222 last_failed_step: suspend 223 suspend 224Field success means the success number of suspend to RAM, and field fail means 225the failure number. Others are the failure number of different steps of suspend 226to RAM. suspend_stats just lists the last 2 failed devices, error number and 227failed step of suspend. 228