51 lines
2.7 KiB
Plaintext
51 lines
2.7 KiB
Plaintext
Suspend notifiers
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(C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL
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There are some operations that device drivers may want to carry out in their
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.suspend() routines, but shouldn't, because they can cause the hibernation or
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suspend to fail. For example, a driver may want to allocate a substantial amount
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of memory (like 50 MB) in .suspend(), but that shouldn't be done after the
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swsusp's memory shrinker has run.
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Also, there may be some operations, that subsystems want to carry out before a
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hibernation/suspend or after a restore/resume, requiring the system to be fully
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functional, so the drivers' .suspend() and .resume() routines are not suitable
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for this purpose. For example, device drivers may want to upload firmware to
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their devices after a restore from a hibernation image, but they cannot do it by
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calling request_firmware() from their .resume() routines (user land processes
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are frozen at this point). The solution may be to load the firmware into
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memory before processes are frozen and upload it from there in the .resume()
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routine. Of course, a hibernation notifier may be used for this purpose.
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The subsystems that have such needs can register suspend notifiers that will be
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called upon the following events by the suspend core:
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PM_HIBERNATION_PREPARE The system is going to hibernate or suspend, tasks will
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be frozen immediately.
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PM_POST_HIBERNATION The system memory state has been restored from a
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hibernation image or an error occured during the
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hibernation. Device drivers' .resume() callbacks have
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been executed and tasks have been thawed.
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PM_SUSPEND_PREPARE The system is preparing for a suspend.
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PM_POST_SUSPEND The system has just resumed or an error occured during
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the suspend. Device drivers' .resume() callbacks have
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been executed and tasks have been thawed.
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It is generally assumed that whatever the notifiers do for
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PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION. Analogously,
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operations performed for PM_SUSPEND_PREPARE should be reversed for
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PM_POST_SUSPEND. Additionally, all of the notifiers are called for
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PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and
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all of the notifiers are called for PM_POST_SUSPEND if one of them fails for
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PM_SUSPEND_PREPARE.
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The hibernation and suspend notifiers are called with pm_mutex held. They are
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defined in the usual way, but their last argument is meaningless (it is always
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NULL). To register and/or unregister a suspend notifier use the functions
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register_pm_notifier() and unregister_pm_notifier(), respectively, defined in
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include/linux/suspend.h . If you don't need to unregister the notifier, you can
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also use the pm_notifier() macro defined in include/linux/suspend.h .
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