5b79520212
Add a paragraph in Documentation/SubmittingDrivers requesting that the basic PM support be provided by new device drivers. Add two new documents in Documentation/power/ giving general instructions on debugging the suspend/resume functionality and testing the suspend and resume support in device drivers. Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> Cc: Pavel Machek <pavel@ucw.cz> Cc: David Brownell <david-b@pacbell.net> Cc: Nigel Cunningham <ncunningham@linuxmail.org> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
106 lines
5.2 KiB
Text
106 lines
5.2 KiB
Text
Debugging suspend and resume
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(C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL
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1. Testing suspend to disk (STD)
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To verify that the STD works, you can try to suspend in the "reboot" mode:
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# echo reboot > /sys/power/disk
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# echo disk > /sys/power/state
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and the system should suspend, reboot, resume and get back to the command prompt
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where you have started the transition. If that happens, the STD is most likely
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to work correctly, but you need to repeat the test at least a couple of times in
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a row for confidence. This is necessary, because some problems only show up on
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a second attempt at suspending and resuming the system. You should also test
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the "platform" and "shutdown" modes of suspend:
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# echo platform > /sys/power/disk
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# echo disk > /sys/power/state
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or
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# echo shutdown > /sys/power/disk
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# echo disk > /sys/power/state
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in which cases you will have to press the power button to make the system
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resume. If that does not work, you will need to identify what goes wrong.
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a) Test mode of STD
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To verify if there are any drivers that cause problems you can run the STD
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in the test mode:
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# echo test > /sys/power/disk
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# echo disk > /sys/power/state
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in which case the system should freeze tasks, suspend devices, disable nonboot
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CPUs (if any), wait for 5 seconds, enable nonboot CPUs, resume devices, thaw
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tasks and return to your command prompt. If that fails, most likely there is
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a driver that fails to either suspend or resume (in the latter case the system
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may hang or be unstable after the test, so please take that into consideration).
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To find this driver, you can carry out a binary search according to the rules:
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- if the test fails, unload a half of the drivers currently loaded and repeat
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(that would probably involve rebooting the system, so always note what drivers
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have been loaded before the test),
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- if the test succeeds, load a half of the drivers you have unloaded most
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recently and repeat.
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Once you have found the failing driver (there can be more than just one of
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them), you have to unload it every time before the STD transition. In that case
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please make sure to report the problem with the driver.
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It is also possible that a cycle can still fail after you have unloaded
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all modules. In that case, you would want to look in your kernel configuration
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for the drivers that can be compiled as modules (testing again with them as
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modules), and possibly also try boot time options such as "noapic" or "noacpi".
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b) Testing minimal configuration
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If the test mode of STD works, you can boot the system with "init=/bin/bash"
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and attempt to suspend in the "reboot", "shutdown" and "platform" modes. If
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that does not work, there probably is a problem with a driver statically
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compiled into the kernel and you can try to compile more drivers as modules,
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so that they can be tested individually. Otherwise, there is a problem with a
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modular driver and you can find it by loading a half of the modules you normally
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use and binary searching in accordance with the algorithm:
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- if there are n modules loaded and the attempt to suspend and resume fails,
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unload n/2 of the modules and try again (that would probably involve rebooting
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the system),
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- if there are n modules loaded and the attempt to suspend and resume succeeds,
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load n/2 modules more and try again.
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Again, if you find the offending module(s), it(they) must be unloaded every time
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before the STD transition, and please report the problem with it(them).
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c) Advanced debugging
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In case the STD does not work on your system even in the minimal configuration
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and compiling more drivers as modules is not practical or some modules cannot
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be unloaded, you can use one of the more advanced debugging techniques to find
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the problem. First, if there is a serial port in your box, you can set the
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CONFIG_DISABLE_CONSOLE_SUSPEND kernel configuration option and try to log kernel
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messages using the serial console. This may provide you with some information
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about the reasons of the suspend (resume) failure. Alternatively, it may be
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possible to use a FireWire port for debugging with firescope
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(ftp://ftp.firstfloor.org/pub/ak/firescope/). On i386 it is also possible to
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use the PM_TRACE mechanism documented in Documentation/s2ram.txt .
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2. Testing suspend to RAM (STR)
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To verify that the STR works, it is generally more convenient to use the s2ram
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tool available from http://suspend.sf.net and documented at
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http://en.opensuse.org/s2ram . However, before doing that it is recommended to
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carry out the procedure described in section 1.
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Assume you have resolved the problems with the STD and you have found some
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failing drivers. These drivers are also likely to fail during the STR or
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during the resume, so it is better to unload them every time before the STR
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transition. Now, you can follow the instructions at
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http://en.opensuse.org/s2ram to test the system, but if it does not work
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"out of the box", you may need to boot it with "init=/bin/bash" and test
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s2ram in the minimal configuration. In that case, you may be able to search
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for failing drivers by following the procedure analogous to the one described in
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1b). If you find some failing drivers, you will have to unload them every time
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before the STR transition (ie. before you run s2ram), and please report the
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problems with them.
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