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b10d9117 RW |
1 | Suspend notifiers |
2 | (C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL | |
3 | ||
4 | There 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 | |
6 | suspend to fail. For example, a driver may want to allocate a substantial amount | |
7 | of memory (like 50 MB) in .suspend(), but that shouldn't be done after the | |
8 | swsusp's memory shrinker has run. | |
9 | ||
10 | Also, there may be some operations, that subsystems want to carry out before a | |
11 | hibernation/suspend or after a restore/resume, requiring the system to be fully | |
12 | functional, so the drivers' .suspend() and .resume() routines are not suitable | |
13 | for this purpose. For example, device drivers may want to upload firmware to | |
14 | their devices after a restore from a hibernation image, but they cannot do it by | |
15 | calling request_firmware() from their .resume() routines (user land processes | |
16 | are frozen at this point). The solution may be to load the firmware into | |
17 | memory before processes are frozen and upload it from there in the .resume() | |
18 | routine. Of course, a hibernation notifier may be used for this purpose. | |
19 | ||
20 | The subsystems that have such needs can register suspend notifiers that will be | |
21 | called upon the following events by the suspend core: | |
22 | ||
23 | PM_HIBERNATION_PREPARE The system is going to hibernate or suspend, tasks will | |
24 | be frozen immediately. | |
25 | ||
26 | PM_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 | ||
c3e94d89 AS |
31 | PM_RESTORE_PREPARE The system is going to restore a hibernation image. |
32 | If all goes well the restored kernel will issue a | |
33 | PM_POST_HIBERNATION notification. | |
34 | ||
35 | PM_POST_RESTORE An error occurred during the hibernation restore. | |
36 | Device drivers' .resume() callbacks have been executed | |
37 | and tasks have been thawed. | |
38 | ||
b10d9117 RW |
39 | PM_SUSPEND_PREPARE The system is preparing for a suspend. |
40 | ||
41 | PM_POST_SUSPEND The system has just resumed or an error occured during | |
42 | the suspend. Device drivers' .resume() callbacks have | |
43 | been executed and tasks have been thawed. | |
44 | ||
45 | It is generally assumed that whatever the notifiers do for | |
46 | PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION. Analogously, | |
47 | operations performed for PM_SUSPEND_PREPARE should be reversed for | |
48 | PM_POST_SUSPEND. Additionally, all of the notifiers are called for | |
49 | PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and | |
50 | all of the notifiers are called for PM_POST_SUSPEND if one of them fails for | |
51 | PM_SUSPEND_PREPARE. | |
52 | ||
53 | The hibernation and suspend notifiers are called with pm_mutex held. They are | |
54 | defined in the usual way, but their last argument is meaningless (it is always | |
55 | NULL). To register and/or unregister a suspend notifier use the functions | |
56 | register_pm_notifier() and unregister_pm_notifier(), respectively, defined in | |
57 | include/linux/suspend.h . If you don't need to unregister the notifier, you can | |
58 | also use the pm_notifier() macro defined in include/linux/suspend.h . |