Documentation/power/notifiers.txt - linux - Git at Google

 Suspend notifiers
 	(C) 2007-2011 Rafael J. Wysocki <rjw@sisk.pl>, 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, tasks will be frozen
 			immediately. This is different from PM_SUSPEND_PREPARE
 			below because here we do additional work between notifiers
 			and drivers freezing.

 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
 PM_SUSPEND_PREPARE.

 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 .
	Suspend notifiers
	(C) 2007-2011 Rafael J. Wysocki <rjw@sisk.pl>, 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, tasks will be frozen
	immediately. This is different from PM_SUSPEND_PREPARE
	below because here we do additional work between notifiers
	and drivers freezing.

	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
	PM_SUSPEND_PREPARE.

	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 .