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Documentation / power / notifiers.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

1	Suspend notifiers
2		(C) 2007-2011 Rafael J. Wysocki <rjw@sisk.pl>, GPL
3	
4	There are some operations that subsystems or drivers may want to carry out
5	before hibernation/suspend or after restore/resume, but they require the system
6	to be fully functional, so the drivers' and subsystems' .suspend() and .resume()
7	or even .prepare() and .complete() callbacks are not suitable for this purpose.
8	For example, device drivers may want to upload firmware to their devices after
9	resume/restore, but they cannot do it by calling request_firmware() from their
10	.resume() or .complete() routines (user land processes are frozen at these
11	points).  The solution may be to load the firmware into memory before processes
12	are frozen and upload it from there in the .resume() routine.
13	A suspend/hibernation notifier may be used for this purpose.
14	
15	The subsystems or drivers having such needs can register suspend notifiers that
16	will be called upon the following events by the PM core:
17	
18	PM_HIBERNATION_PREPARE	The system is going to hibernate, tasks will be frozen
19				immediately. This is different from PM_SUSPEND_PREPARE
20				below because here we do additional work between notifiers
21				and drivers freezing.
22	
23	PM_POST_HIBERNATION	The system memory state has been restored from a
24				hibernation image or an error occurred during
25				hibernation.  Device drivers' restore callbacks have
26				been executed and tasks have been thawed.
27	
28	PM_RESTORE_PREPARE	The system is going to restore a hibernation image.
29				If all goes well, the restored kernel will issue a
30				PM_POST_HIBERNATION notification.
31	
32	PM_POST_RESTORE		An error occurred during restore from hibernation.
33				Device drivers' restore callbacks have been executed
34				and tasks have been thawed.
35	
36	PM_SUSPEND_PREPARE	The system is preparing for suspend.
37	
38	PM_POST_SUSPEND		The system has just resumed or an error occurred during
39				suspend.  Device drivers' resume callbacks have been
40				executed and tasks have been thawed.
41	
42	It is generally assumed that whatever the notifiers do for
43	PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION.  Analogously,
44	operations performed for PM_SUSPEND_PREPARE should be reversed for
45	PM_POST_SUSPEND.  Additionally, all of the notifiers are called for
46	PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and
47	all of the notifiers are called for PM_POST_SUSPEND if one of them fails for
48	PM_SUSPEND_PREPARE.
49	
50	The hibernation and suspend notifiers are called with pm_mutex held.  They are
51	defined in the usual way, but their last argument is meaningless (it is always
52	NULL).  To register and/or unregister a suspend notifier use the functions
53	register_pm_notifier() and unregister_pm_notifier(), respectively, defined in
54	include/linux/suspend.h .  If you don't need to unregister the notifier, you can
55	also use the pm_notifier() macro defined in include/linux/suspend.h .
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