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If device drivers allocate substantial amounts of memory (above 1 MB) in their hibernate .freeze() callbacks (or in their legacy suspend callbcks during hibernation), the subsequent creation of hibernate image may fail due to the lack of memory. This is the case, because the drivers' .freeze() callbacks are executed after the hibernate memory preallocation has been carried out and the preallocated amount of memory may be too small to cover the new driver allocations. Unfortunately, the drivers' .prepare() callbacks also are executed after the hibernate memory preallocation has completed, so they are not suitable for allocating additional memory either. Thus the only way a driver can safely allocate memory during hibernation is to use a hibernate/suspend notifier. However, the notifiers are called before the freezing of user space and the drivers wanting to use them for allocating additional memory may not know how much memory needs to be allocated at that point. To let device drivers overcome this difficulty rework the hibernation sequence so that the memory preallocation is carried out after the drivers' .prepare() callbacks have been executed, so that the .prepare() callbacks can be used for allocating additional memory to be used by the drivers' .freeze() callbacks. Update documentation to match the new behavior of the code. Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
54 lines
2.7 KiB
Plaintext
54 lines
2.7 KiB
Plaintext
Suspend notifiers
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(C) 2007-2011 Rafael J. Wysocki <rjw@sisk.pl>, GPL
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There are some operations that subsystems or drivers may want to carry out
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before hibernation/suspend or after restore/resume, but they require the system
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to be fully functional, so the drivers' and subsystems' .suspend() and .resume()
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or even .prepare() and .complete() callbacks are not suitable for this purpose.
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For example, device drivers may want to upload firmware to their devices after
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resume/restore, but they cannot do it by calling request_firmware() from their
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.resume() or .complete() routines (user land processes are frozen at these
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points). The solution may be to load the firmware into memory before processes
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are frozen and upload it from there in the .resume() routine.
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A suspend/hibernation notifier may be used for this purpose.
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The subsystems or drivers having such needs can register suspend notifiers that
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will be called upon the following events by the PM core:
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PM_HIBERNATION_PREPARE The system is going to hibernate or suspend, tasks will
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be frozen immediately.
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PM_POST_HIBERNATION The system memory state has been restored from a
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hibernation image or an error occurred during
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hibernation. Device drivers' restore callbacks have
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been executed and tasks have been thawed.
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PM_RESTORE_PREPARE The system is going to restore a hibernation image.
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If all goes well, the restored kernel will issue a
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PM_POST_HIBERNATION notification.
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PM_POST_RESTORE An error occurred during restore from hibernation.
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Device drivers' restore callbacks have been executed
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and tasks have been thawed.
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PM_SUSPEND_PREPARE The system is preparing for suspend.
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PM_POST_SUSPEND The system has just resumed or an error occurred during
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suspend. Device drivers' resume callbacks have been
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executed and tasks have been thawed.
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It is generally assumed that whatever the notifiers do for
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PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION. Analogously,
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operations performed for PM_SUSPEND_PREPARE should be reversed for
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PM_POST_SUSPEND. Additionally, all of the notifiers are called for
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PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and
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all of the notifiers are called for PM_POST_SUSPEND if one of them fails for
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PM_SUSPEND_PREPARE.
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The hibernation and suspend notifiers are called with pm_mutex held. They are
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defined in the usual way, but their last argument is meaningless (it is always
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NULL). To register and/or unregister a suspend notifier use the functions
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register_pm_notifier() and unregister_pm_notifier(), respectively, defined in
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include/linux/suspend.h . If you don't need to unregister the notifier, you can
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also use the pm_notifier() macro defined in include/linux/suspend.h .
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