71 lines
3.1 KiB
ReStructuredText
71 lines
3.1 KiB
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=============================
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Suspend/Hibernation Notifiers
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=============================
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::
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Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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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
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``->resume()`` or even ``->prepare()`` and ``->complete()`` callbacks are not
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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 :c:func:`request_firmware()`
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from their ``->resume()`` or ``->complete()`` callback routines (user land
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processes are frozen at these points). The solution may be to load the firmware
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into memory before processes are frozen and upload it from there in the
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``->resume()`` routine. A suspend/hibernation notifier may be used for that.
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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``
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The system is going to hibernate, tasks will be frozen immediately. This
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is different from ``PM_SUSPEND_PREPARE`` below, because in this case
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additional work is done between the notifiers and the invocation of PM
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callbacks for the "freeze" transition.
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``PM_POST_HIBERNATION``
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The system memory state has been restored from a hibernation image or an
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error occurred during hibernation. Device restore callbacks have been
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executed and tasks have been thawed.
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``PM_RESTORE_PREPARE``
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The system is going to restore a hibernation image. If all goes well,
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the restored image kernel will issue a ``PM_POST_HIBERNATION``
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notification.
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``PM_POST_RESTORE``
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An error occurred during restore from hibernation. Device restore
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callbacks have been executed and tasks have been thawed.
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``PM_SUSPEND_PREPARE``
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The system is preparing for suspend.
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``PM_POST_SUSPEND``
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The system has just resumed or an error occurred during suspend. Device
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resume callbacks have been 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``.
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Analogously, operations carried out for ``PM_SUSPEND_PREPARE`` should be
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reversed for ``PM_POST_SUSPEND``.
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Moreover, if one of the notifiers fails for the ``PM_HIBERNATION_PREPARE`` or
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``PM_SUSPEND_PREPARE`` event, the notifiers that have already succeeded for that
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event will be called for ``PM_POST_HIBERNATION`` or ``PM_POST_SUSPEND``,
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respectively.
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The hibernation and suspend notifiers are called with :c:data:`pm_mutex` held.
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They are defined in the usual way, but their last argument is meaningless (it is
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always NULL).
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To register and/or unregister a suspend notifier use
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:c:func:`register_pm_notifier()` and :c:func:`unregister_pm_notifier()`,
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respectively (both defined in :file:`include/linux/suspend.h`). If you don't
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need to unregister the notifier, you can also use the :c:func:`pm_notifier()`
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macro defined in :file:`include/linux/suspend.h`.
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