Based on kernel version 3.9. Page generated on 2013-05-02 23:12 EST.
1 Debugging hibernation and suspend 2 (C) 2007 Rafael J. Wysocki <firstname.lastname@example.org>, GPL 3 4 1. Testing hibernation (aka suspend to disk or STD) 5 6 To 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 11 and the system should create a hibernation image, reboot, resume and get back to 12 the command prompt where you have started the transition. If that happens, 13 hibernation is most likely to work correctly. Still, you need to repeat the 14 test at least a couple of times in a row for confidence. [This is necessary, 15 because some problems only show up on a second attempt at suspending and 16 resuming the system.] Moreover, hibernating in the "reboot" and "shutdown" 17 modes causes the PM core to skip some platform-related callbacks which on ACPI 18 systems might be necessary to make hibernation work. Thus, if your machine fails 19 to 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 24 which is the default and recommended mode of hibernation. 25 26 Unfortunately, the "platform" mode of hibernation does not work on some systems 27 with broken BIOSes. In such cases the "shutdown" mode of hibernation might 28 work: 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 34 button to make the system resume). 35 36 If neither "platform" nor "shutdown" hibernation mode works, you will need to 37 identify what goes wrong. 38 39 a) Test modes of hibernation 40 41 To find out why hibernation fails on your system, you can use a special testing 42 facility available if the kernel is compiled with CONFIG_PM_DEBUG set. Then, 43 there is the file /sys/power/pm_test that can be used to make the hibernation 44 core run in a test mode. There are 5 test modes available: 45 46 freezer 47 - test the freezing of processes 48 49 devices 50 - test the freezing of processes and suspending of devices 51 52 platform 53 - test the freezing of processes, suspending of devices and platform 54 global control methods(*) 55 56 processors 57 - test the freezing of processes, suspending of devices, platform 58 global control methods(*) and the disabling of nonboot CPUs 59 60 core 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 68 To 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 70 suspending devices) and issue the standard hibernation commands. For example, 71 to use the "devices" test mode along with the "platform" mode of hibernation, 72 you 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 78 Then, the kernel will try to freeze processes, suspend devices, wait 5 seconds, 79 resume devices and thaw processes. If "platform" is written to 80 /sys/power/pm_test , then after suspending devices the kernel will additionally 81 invoke the global control methods (eg. ACPI global control methods) used to 82 prepare the platform firmware for hibernation. Next, it will wait 5 seconds and 83 invoke the platform (eg. ACPI) global methods used to cancel hibernation etc. 84 85 Writing "none" to /sys/power/pm_test causes the kernel to switch to the normal 86 hibernation/suspend operations. Also, when open for reading, /sys/power/pm_test 87 contains a space-separated list of all available tests (including "none" that 88 represents the normal functionality) in which the current test level is 89 indicated by square brackets. 90 91 Generally, as you can see, each test level is more "invasive" than the previous 92 one and the "core" level tests the hardware and drivers as deeply as possible 93 without creating a hibernation image. Obviously, if the "devices" test fails, 94 the "platform" test will fail as well and so on. Thus, as a rule of thumb, you 95 should try the test modes starting from "freezer", through "devices", "platform" 96 and "processors" up to "core" (repeat the test on each level a couple of times 97 to make sure that any random factors are avoided). 98 99 If the "freezer" test fails, there is a task that cannot be frozen (in that case 100 it usually is possible to identify the offending task by analysing the output of 101 dmesg obtained after the failing test). Failure at this level usually means 102 that there is a problem with the tasks freezer subsystem that should be 103 reported. 104 105 If the "devices" test fails, most likely there is a driver that cannot suspend 106 or resume its device (in the latter case the system may hang or become unstable 107 after the test, so please take that into consideration). To find this driver, 108 you 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 111 have been loaded before the test), 112 - if the test succeeds, load a half of the drivers you have unloaded most 113 recently and repeat. 114 115 Once you have found the failing driver (there can be more than just one of 116 them), you have to unload it every time before hibernation. In that case please 117 make sure to report the problem with the driver. 118 119 It is also possible that the "devices" test will still fail after you have 120 unloaded all modules. In that case, you may want to look in your kernel 121 configuration for the drivers that can be compiled as modules (and test again 122 with these drivers compiled as modules). You may also try to use some special 123 kernel command line options such as "noapic", "noacpi" or even "acpi=off". 124 125 If the "platform" test fails, there is a problem with the handling of the 126 platform (eg. ACPI) firmware on your system. In that case the "platform" mode 127 of hibernation is not likely to work. You can try the "shutdown" mode, but that 128 is rather a poor man's workaround. 129 130 If the "processors" test fails, the disabling/enabling of nonboot CPUs does not 131 work (of course, this only may be an issue on SMP systems) and the problem 132 should be reported. In that case you can also try to switch the nonboot CPUs 133 off and on using the /sys/devices/system/cpu/cpu*/online sysfs attributes and 134 see if that works. 135 136 If the "core" test fails, which means that suspending of the system/platform 137 devices has failed (these devices are suspended on one CPU with interrupts off), 138 the problem is most probably hardware-related and serious, so it should be 139 reported. 140 141 A failure of any of the "platform", "processors" or "core" tests may cause your 142 system to hang or become unstable, so please beware. Such a failure usually 143 indicates a serious problem that very well may be related to the hardware, but 144 please report it anyway. 145 146 b) Testing minimal configuration 147 148 If 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 151 probably is a problem with a driver statically compiled into the kernel and you 152 can try to compile more drivers as modules, so that they can be tested 153 individually. Otherwise, there is a problem with a modular driver and you can 154 find it by loading a half of the modules you normally use and binary searching 155 in accordance with the algorithm: 156 - if there are n modules loaded and the attempt to suspend and resume fails, 157 unload n/2 of the modules and try again (that would probably involve rebooting 158 the system), 159 - if there are n modules loaded and the attempt to suspend and resume succeeds, 160 load n/2 modules more and try again. 161 162 Again, if you find the offending module(s), it(they) must be unloaded every time 163 before hibernation, and please report the problem with it(them). 164 165 c) Advanced debugging 166 167 In case that hibernation does not work on your system even in the minimal 168 configuration and compiling more drivers as modules is not practical or some 169 modules cannot be unloaded, you can use one of the more advanced debugging 170 techniques to find the problem. First, if there is a serial port in your box, 171 you can boot the kernel with the 'no_console_suspend' parameter and try to log 172 kernel messages using the serial console. This may provide you with some 173 information about the reasons of the suspend (resume) failure. Alternatively, 174 it 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 176 use the PM_TRACE mechanism documented in Documentation/power/s2ram.txt . 177 178 2. Testing suspend to RAM (STR) 179 180 To verify that the STR works, it is generally more convenient to use the s2ram 181 tool available from http://suspend.sf.net and documented at 182 http://en.opensuse.org/SDB:Suspend_to_RAM. 183 184 Namely, after writing "freezer", "devices", "platform", "processors", or "core" 185 into /sys/power/pm_test (available if the kernel is compiled with 186 CONFIG_PM_DEBUG set) the suspend code will work in the test mode corresponding 187 to given string. The STR test modes are defined in the same way as for 188 hibernation, so please refer to Section 1 for more information about them. In 189 particular, the "core" test allows you to test everything except for the actual 190 invocation of the platform firmware in order to put the system into the sleep 191 state. 192 193 Among other things, the testing with the help of /sys/power/pm_test may allow 194 you to identify drivers that fail to suspend or resume their devices. They 195 should be unloaded every time before an STR transition. 196 197 Next, you can follow the instructions at http://en.opensuse.org/s2ram to test 198 the system, but if it does not work "out of the box", you may need to boot it 199 with "init=/bin/bash" and test s2ram in the minimal configuration. In that 200 case, you may be able to search for failing drivers by following the procedure 201 analogous to the one described in section 1. If you find some failing drivers, 202 you will have to unload them every time before an STR transition (ie. before 203 you run s2ram), and please report the problems with them. 204 205 There is a debugfs entry which shows the suspend to RAM statistics. Here is an 206 example 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 224 Field success means the success number of suspend to RAM, and field fail means 225 the failure number. Others are the failure number of different steps of suspend 226 to RAM. suspend_stats just lists the last 2 failed devices, error number and 227 failed step of suspend.