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authorRafael J. Wysocki <rjw@sisk.pl>2010-07-05 22:43:53 +0200
committerRafael J. Wysocki <rjw@sisk.pl>2010-07-19 01:58:48 +0200
commitc125e96f044427f38d106fab7bc5e4a5e6a18262 (patch)
treed9bbd40cc933fe522dbdf8ca2f7edf7b6f2f7ca4 /Documentation/ABI
parentb14e033e17d0ea0ba12668d0d2f371cd31586994 (diff)
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PM: Make it possible to avoid races between wakeup and system sleep
One of the arguments during the suspend blockers discussion was that the mainline kernel didn't contain any mechanisms making it possible to avoid races between wakeup and system suspend. Generally, there are two problems in that area. First, if a wakeup event occurs exactly when /sys/power/state is being written to, it may be delivered to user space right before the freezer kicks in, so the user space consumer of the event may not be able to process it before the system is suspended. Second, if a wakeup event occurs after user space has been frozen, it is not generally guaranteed that the ongoing transition of the system into a sleep state will be aborted. To address these issues introduce a new global sysfs attribute, /sys/power/wakeup_count, associated with a running counter of wakeup events and three helper functions, pm_stay_awake(), pm_relax(), and pm_wakeup_event(), that may be used by kernel subsystems to control the behavior of this attribute and to request the PM core to abort system transitions into a sleep state already in progress. The /sys/power/wakeup_count file may be read from or written to by user space. Reads will always succeed (unless interrupted by a signal) and return the current value of the wakeup events counter. Writes, however, will only succeed if the written number is equal to the current value of the wakeup events counter. If a write is successful, it will cause the kernel to save the current value of the wakeup events counter and to abort the subsequent system transition into a sleep state if any wakeup events are reported after the write has returned. [The assumption is that before writing to /sys/power/state user space will first read from /sys/power/wakeup_count. Next, user space consumers of wakeup events will have a chance to acknowledge or veto the upcoming system transition to a sleep state. Finally, if the transition is allowed to proceed, /sys/power/wakeup_count will be written to and if that succeeds, /sys/power/state will be written to as well. Still, if any wakeup events are reported to the PM core by kernel subsystems after that point, the transition will be aborted.] Additionally, put a wakeup events counter into struct dev_pm_info and make these per-device wakeup event counters available via sysfs, so that it's possible to check the activity of various wakeup event sources within the kernel. To illustrate how subsystems can use pm_wakeup_event(), make the low-level PCI runtime PM wakeup-handling code use it. Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org> Acked-by: Greg Kroah-Hartman <gregkh@suse.de> Acked-by: markgross <markgross@thegnar.org> Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Diffstat (limited to 'Documentation/ABI')
-rw-r--r--Documentation/ABI/testing/sysfs-power15
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index d6a801f..2875f1f 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -114,3 +114,18 @@ Description:
if this file contains "1", which is the default. It may be
disabled by writing "0" to this file, in which case all devices
will be suspended and resumed synchronously.
+
+What: /sys/power/wakeup_count
+Date: July 2010
+Contact: Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+ The /sys/power/wakeup_count file allows user space to put the
+ system into a sleep state while taking into account the
+ concurrent arrival of wakeup events. Reading from it returns
+ the current number of registered wakeup events and it blocks if
+ some wakeup events are being processed at the time the file is
+ read from. Writing to it will only succeed if the current
+ number of wakeup events is equal to the written value and, if
+ successful, will make the kernel abort a subsequent transition
+ to a sleep state if any wakeup events are reported after the
+ write has returned.
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