Commit 730c4c05 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki Committed by Jonathan Corbet

PM / sleep / docs: Convert PM notifiers document to reST

Move the document describing PM notifiers (used during system sleep
state transitions) to Documentation/driver-api/pm/, convert it to reST
and update it to use current terminology.  Also replace the remaining
references to the old version of it in .txt documents with references
to the new one.
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 2728b2d2
...@@ -620,7 +620,7 @@ been thawed. Generally speaking, the PM notifiers are suitable for performing ...@@ -620,7 +620,7 @@ been thawed. Generally speaking, the PM notifiers are suitable for performing
actions that either require user space to be available, or at least won't actions that either require user space to be available, or at least won't
interfere with user space. interfere with user space.
For details refer to :file:`Documentation/power/notifiers.txt`. For details refer to :doc:`notifiers`.
Device Low-Power (suspend) States Device Low-Power (suspend) States
......
...@@ -5,6 +5,7 @@ Device Power Management ...@@ -5,6 +5,7 @@ Device Power Management
.. toctree:: .. toctree::
devices devices
notifiers
types types
.. only:: subproject and html .. only:: subproject and html
......
=============================
Suspend/Hibernation Notifiers
=============================
::
Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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 :c:func:`request_firmware()`
from their ``->resume()`` or ``->complete()`` callback 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 that.
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 in this case
additional work is done between the notifiers and the invocation of PM
callbacks for the "freeze" transition.
``PM_POST_HIBERNATION``
The system memory state has been restored from a hibernation image or an
error occurred during hibernation. Device 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 image kernel will issue a ``PM_POST_HIBERNATION``
notification.
``PM_POST_RESTORE``
An error occurred during restore from hibernation. Device 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
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 carried out for ``PM_SUSPEND_PREPARE`` should be
reversed for ``PM_POST_SUSPEND``.
Moreover, if one of the notifiers fails for the ``PM_HIBERNATION_PREPARE`` or
``PM_SUSPEND_PREPARE`` event, the notifiers that have already succeeded for that
event will be called for ``PM_POST_HIBERNATION`` or ``PM_POST_SUSPEND``,
respectively.
The hibernation and suspend notifiers are called with :c:data:`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
:c:func:`register_pm_notifier()` and :c:func:`unregister_pm_notifier()`,
respectively (both defined in :file:`include/linux/suspend.h`). If you don't
need to unregister the notifier, you can also use the :c:func:`pm_notifier()`
macro defined in :file:`include/linux/suspend.h`.
...@@ -14,8 +14,6 @@ freezing-of-tasks.txt ...@@ -14,8 +14,6 @@ freezing-of-tasks.txt
- How processes and controlled during suspend - How processes and controlled during suspend
interface.txt interface.txt
- Power management user interface in /sys/power - Power management user interface in /sys/power
notifiers.txt
- Registering suspend notifiers in device drivers
opp.txt opp.txt
- Operating Performance Point library - Operating Performance Point library
pci.txt pci.txt
......
...@@ -197,7 +197,8 @@ tasks, since it generally exists anyway. ...@@ -197,7 +197,8 @@ tasks, since it generally exists anyway.
A driver must have all firmwares it may need in RAM before suspend() is called. A driver must have all firmwares it may need in RAM before suspend() is called.
If keeping them is not practical, for example due to their size, they must be If keeping them is not practical, for example due to their size, they must be
requested early enough using the suspend notifier API described in notifiers.txt. requested early enough using the suspend notifier API described in
Documentation/driver-api/pm/notifiers.rst.
VI. Are there any precautions to be taken to prevent freezing failures? VI. Are there any precautions to be taken to prevent freezing failures?
......
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 .
...@@ -713,7 +713,7 @@ In addition to that the prepare() callback may carry out some operations ...@@ -713,7 +713,7 @@ In addition to that the prepare() callback may carry out some operations
preparing the device to be suspended, although it should not allocate memory preparing the device to be suspended, although it should not allocate memory
(if additional memory is required to suspend the device, it has to be (if additional memory is required to suspend the device, it has to be
preallocated earlier, for example in a suspend/hibernate notifier as described preallocated earlier, for example in a suspend/hibernate notifier as described
in Documentation/power/notifiers.txt). in Documentation/driver-api/pm/notifiers.rst).
3.1.2. suspend() 3.1.2. suspend()
......
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