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_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 35PM_POST_RESTORE An error occurred during the hibernation restore. 36 Device drivers' .resume() callbacks have been executed 37 and tasks have been thawed. 38 39PM_SUSPEND_PREPARE The system is preparing for a suspend. 40 41PM_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 45It is generally assumed that whatever the notifiers do for 46PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION. Analogously, 47operations performed for PM_SUSPEND_PREPARE should be reversed for 48PM_POST_SUSPEND. Additionally, all of the notifiers are called for 49PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and 50all of the notifiers are called for PM_POST_SUSPEND if one of them fails for 51PM_SUSPEND_PREPARE. 52 53The hibernation and suspend notifiers are called with pm_mutex held. They are 54defined in the usual way, but their last argument is meaningless (it is always 55NULL). To register and/or unregister a suspend notifier use the functions 56register_pm_notifier() and unregister_pm_notifier(), respectively, defined in 57include/linux/suspend.h . If you don't need to unregister the notifier, you can 58also use the pm_notifier() macro defined in include/linux/suspend.h . 59