path: root/Documentation
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authorAlan Stern <stern@rowland.harvard.edu>2011-11-03 23:39:18 +0100
committerRafael J. Wysocki <rjw@sisk.pl>2011-11-04 22:28:14 +0100
commit886486b792e4f6f96d4fbe8ec5bf20811cab7d6a (patch)
tree1c638e14492c16f8f69ca71fa93b2d81d8e4eeb6 /Documentation
parent6513fd6972f725291ee8ce62c7a39fb8a6c7391e (diff)
PM / Runtime: Automatically retry failed autosuspends
Originally, the runtime PM core would send an idle notification whenever a suspend attempt failed. The idle callback routine could then schedule a delayed suspend for some time later. However this behavior was changed by commit f71648d73c1650b8b4aceb3856bebbde6daa3b86 (PM / Runtime: Remove idle notification after failing suspend). No notifications were sent, and there was no clear mechanism to retry failed suspends. This caused problems for the usbhid driver, because it fails autosuspend attempts as long as a key is being held down. Therefore this patch (as1492) adds a mechanism for retrying failed autosuspends. If the callback routine updates the last_busy field so that the next autosuspend expiration time is in the future, the autosuspend will automatically be rescheduled. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Tested-by: Henrik Rydberg <rydberg@euromail.se> Cc: <stable@kernel.org> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Diffstat (limited to 'Documentation')
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
index 0e856088db7..5336149f831 100644
--- a/Documentation/power/runtime_pm.txt
+++ b/Documentation/power/runtime_pm.txt
@@ -789,6 +789,16 @@ will behave normally, not taking the autosuspend delay into account.
Similarly, if the power.use_autosuspend field isn't set then the autosuspend
helper functions will behave just like the non-autosuspend counterparts.
+Under some circumstances a driver or subsystem may want to prevent a device
+from autosuspending immediately, even though the usage counter is zero and the
+autosuspend delay time has expired. If the ->runtime_suspend() callback
+returns -EAGAIN or -EBUSY, and if the next autosuspend delay expiration time is
+in the future (as it normally would be if the callback invoked
+pm_runtime_mark_last_busy()), the PM core will automatically reschedule the
+autosuspend. The ->runtime_suspend() callback can't do this rescheduling
+itself because no suspend requests of any kind are accepted while the device is
+suspending (i.e., while the callback is running).
The implementation is well suited for asynchronous use in interrupt contexts.
However such use inevitably involves races, because the PM core can't
synchronize ->runtime_suspend() callbacks with the arrival of I/O requests.