Debugging suspend and resume	(C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL1. Testing suspend to disk (STD)To verify that the STD works, you can try to suspend in the "reboot" mode:# echo reboot > /sys/power/disk# echo disk > /sys/power/stateand the system should suspend, reboot, resume and get back to the command promptwhere you have started the transition.  If that happens, the STD is most likelyto work correctly, but you need to repeat the test at least a couple of times ina row for confidence.  This is necessary, because some problems only show up ona second attempt at suspending and resuming the system.  You should also testthe "platform" and "shutdown" modes of suspend:# echo platform > /sys/power/disk# echo disk > /sys/power/stateor# echo shutdown > /sys/power/disk# echo disk > /sys/power/statein which cases you will have to press the power button to make the systemresume.  If that does not work, you will need to identify what goes wrong.a) Test mode of STDTo verify if there are any drivers that cause problems you can run the STDin the test mode:# echo test > /sys/power/disk# echo disk > /sys/power/statein which case the system should freeze tasks, suspend devices, disable nonbootCPUs (if any), wait for 5 seconds, enable nonboot CPUs, resume devices, thawtasks and return to your command prompt.  If that fails, most likely there isa driver that fails to either suspend or resume (in the latter case the systemmay 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:- 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 drivershave been loaded before the test),- if the test succeeds, load a half of the drivers you have unloaded mostrecently and repeat.Once you have found the failing driver (there can be more than just one ofthem), you have to unload it every time before the STD transition.  In that caseplease make sure to report the problem with the driver.It is also possible that a cycle can still fail after you have unloadedall modules. In that case, you would want to look in your kernel configurationfor the drivers that can be compiled as modules (testing again with them asmodules), and possibly also try boot time options such as "noapic" or "noacpi".b) Testing minimal configurationIf 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.  Ifthat does not work, there probably is a problem with a driver staticallycompiled 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 amodular driver and you can find it by loading a half of the modules you normallyuse 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 rebootingthe 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 timebefore the STD transition, and please report the problem with it(them).c) Advanced debuggingIn case the STD does not work on your system even in the minimal configurationand compiling more drivers as modules is not practical or some modules cannotbe unloaded, you can use one of the more advanced debugging techniques to findthe problem.  First, if there is a serial port in your box, you can boot thekernel with the 'no_console_suspend' parameter and try to log kernelmessages using the serial console.  This may provide you with some informationabout the reasons of the suspend (resume) failure.  Alternatively, it may bepossible to use a FireWire port for debugging with firescope(ftp://ftp.firstfloor.org/pub/ak/firescope/).  On i386 it is also possible touse the PM_TRACE mechanism documented in Documentation/s2ram.txt .2. Testing suspend to RAM (STR)To verify that the STR works, it is generally more convenient to use the s2ramtool available from http://suspend.sf.net and documented athttp://en.opensuse.org/s2ram .  However, before doing that it is recommended tocarry out the procedure described in section 1.Assume you have resolved the problems with the STD and you have found somefailing drivers.  These drivers are also likely to fail during the STR orduring the resume, so it is better to unload them every time before the STRtransition.  Now, you can follow the instructions athttp://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 tests2ram in the minimal configuration.  In that case, you may be able to searchfor failing drivers by following the procedure analogous to the one described in1b).  If you find some failing drivers, you will have to unload them every timebefore the STR transition (ie. before you run s2ram), and please report theproblems with them.