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+ (C) 2007-2011 Rafael J. Wysocki <firstname.lastname@example.org>, 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 .