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