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- (C) 2007-2011 Rafael J. Wysocki <email@example.com>, GPL
-There are some operations that subsystems or drivers may want to carry out
-before hibernation/suspend or after restore/resume, but they require the system
-to be fully functional, so the drivers' and subsystems' .suspend() and .resume()
-or even .prepare() and .complete() callbacks are not suitable for this purpose.
-For example, device drivers may want to upload firmware to their devices after
-resume/restore, but they cannot do it by calling request_firmware() from their
-.resume() or .complete() routines (user land processes are frozen at these
-points). The solution may be to load the firmware into memory before processes
-are frozen and upload it from there in the .resume() routine.
-A suspend/hibernation notifier may be used for this purpose.
-The subsystems or drivers having such needs can register suspend notifiers that
-will be called upon the following events by the PM core:
-PM_HIBERNATION_PREPARE The system is going to hibernate or suspend, tasks will
- be frozen immediately.
-PM_POST_HIBERNATION The system memory state has been restored from a
- hibernation image or an error occurred during
- hibernation. Device drivers' restore callbacks have
- been executed and tasks have been thawed.
-PM_RESTORE_PREPARE The system is going to restore a hibernation image.
- If all goes well, the restored kernel will issue a
- PM_POST_HIBERNATION notification.
-PM_POST_RESTORE An error occurred during restore from hibernation.
- Device drivers' restore callbacks have been executed
- and tasks have been thawed.
-PM_SUSPEND_PREPARE The system is preparing for suspend.
-PM_POST_SUSPEND The system has just resumed or an error occurred during
- suspend. Device drivers' resume callbacks have been
- executed and tasks have been thawed.
-It is generally assumed that whatever the notifiers do for
-PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION. Analogously,
-operations performed for PM_SUSPEND_PREPARE should be reversed for
-PM_POST_SUSPEND. Additionally, all of the notifiers are called for
-PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and
-all of the notifiers are called for PM_POST_SUSPEND if one of them fails for
-The hibernation and suspend notifiers are called with pm_mutex held. They are
-defined in the usual way, but their last argument is meaningless (it is always
-NULL). To register and/or unregister a suspend notifier use the functions
-register_pm_notifier() and unregister_pm_notifier(), respectively, defined in
-include/linux/suspend.h . If you don't need to unregister the notifier, you can
-also use the pm_notifier() macro defined in include/linux/suspend.h .