55 lines
2.8 KiB
Text
55 lines
2.8 KiB
Text
Suspend notifiers
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(C) 2007-2011 Rafael J. Wysocki <rjw@sisk.pl>, GPL
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There are some operations that subsystems or drivers may want to carry out
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before hibernation/suspend or after restore/resume, but they require the system
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to be fully functional, so the drivers' and subsystems' .suspend() and .resume()
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or even .prepare() and .complete() callbacks are not suitable for this purpose.
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For example, device drivers may want to upload firmware to their devices after
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resume/restore, but they cannot do it by calling request_firmware() from their
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.resume() or .complete() routines (user land processes are frozen at these
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points). The solution may be to load the firmware into memory before processes
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are frozen and upload it from there in the .resume() routine.
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A suspend/hibernation notifier may be used for this purpose.
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The subsystems or drivers having such needs can register suspend notifiers that
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will be called upon the following events by the PM core:
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PM_HIBERNATION_PREPARE The system is going to hibernate, tasks will be frozen
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immediately. This is different from PM_SUSPEND_PREPARE
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below because here we do additional work between notifiers
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and drivers freezing.
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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 occurred during
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hibernation. Device drivers' restore callbacks have
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been executed and tasks have been thawed.
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PM_RESTORE_PREPARE The system is going to restore a hibernation image.
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If all goes well, the restored kernel will issue a
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PM_POST_HIBERNATION notification.
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PM_POST_RESTORE An error occurred during restore from hibernation.
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Device drivers' restore callbacks have been executed
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and tasks have been thawed.
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PM_SUSPEND_PREPARE The system is preparing for suspend.
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PM_POST_SUSPEND The system has just resumed or an error occurred during
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suspend. Device drivers' resume callbacks have been
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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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