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authorRafael J. Wysocki <rjw@sisk.pl>2011-05-17 23:26:00 +0200
committerRafael J. Wysocki <rjw@sisk.pl>2011-05-17 23:26:00 +0200
commit91e7c75ba93c48a82670d630b9daac92ff70095d (patch)
treeb44ac3dca1d03cce99cccc3f4ce55d4b5475d373 /Documentation/power/notifiers.txt
parentc650da23d59d2c82307380414606774c6d49b8bd (diff)
PM: Allow drivers to allocate memory from .prepare() callbacks safely
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>
Diffstat (limited to 'Documentation/power/notifiers.txt')
-rw-r--r--Documentation/power/notifiers.txt51
1 files changed, 23 insertions, 28 deletions
diff --git a/Documentation/power/notifiers.txt b/Documentation/power/notifiers.txt
index cf980709122a..c2a4a346c0d9 100644
--- a/Documentation/power/notifiers.txt
+++ b/Documentation/power/notifiers.txt
@@ -1,46 +1,41 @@
Suspend notifiers
- (C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL
-
-There are some operations that device drivers may want to carry out in their
-.suspend() routines, but shouldn't, because they can cause the hibernation or
-suspend to fail. For example, a driver may want to allocate a substantial amount
-of memory (like 50 MB) in .suspend(), but that shouldn't be done after the
-swsusp's memory shrinker has run.
-
-Also, there may be some operations, that subsystems want to carry out before a
-hibernation/suspend or after a restore/resume, requiring the system to be fully
-functional, so the drivers' .suspend() and .resume() routines are not suitable
-for this purpose. For example, device drivers may want to upload firmware to
-their devices after a restore from a hibernation image, but they cannot do it by
-calling request_firmware() from their .resume() routines (user land processes
-are frozen at this point). The solution may be to load the firmware into
-memory before processes are frozen and upload it from there in the .resume()
-routine. Of course, a hibernation notifier may be used for this purpose.
-
-The subsystems that have such needs can register suspend notifiers that will be
-called upon the following events by the suspend core:
+ (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 or suspend, tasks will
be frozen immediately.
PM_POST_HIBERNATION The system memory state has been restored from a
- hibernation image or an error occurred during the
- hibernation. Device drivers' .resume() callbacks have
+ 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
+ If all goes well, the restored kernel will issue a
PM_POST_HIBERNATION notification.
-PM_POST_RESTORE An error occurred during the hibernation restore.
- Device drivers' .resume() callbacks have been executed
+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 a suspend.
+PM_SUSPEND_PREPARE The system is preparing for suspend.
PM_POST_SUSPEND The system has just resumed or an error occurred during
- the suspend. Device drivers' .resume() callbacks have
- been executed and tasks have been thawed.
+ 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,