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Diffstat (limited to 'Documentation/power/notifiers.txt')
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diff --git a/Documentation/power/notifiers.txt b/Documentation/power/notifiers.txt new file mode 100644 index 000000000..a81fa2543 --- /dev/null +++ b/Documentation/power/notifiers.txt @@ -0,0 +1,55 @@ +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 . |