PM / Sleep: Implement opportunistic sleep, v2

Introduce a mechanism by which the kernel can trigger global
transitions to a sleep state chosen by user space if there are no
active wakeup sources.

It consists of a new sysfs attribute, /sys/power/autosleep, that
can be written one of the strings returned by reads from
/sys/power/state, an ordered workqueue and a work item carrying out
the "suspend" operations.  If a string representing the system's
sleep state is written to /sys/power/autosleep, the work item
triggering transitions to that state is queued up and it requeues
itself after every execution until user space writes "off" to
/sys/power/autosleep.

That work item enables the detection of wakeup events using the
functions already defined in drivers/base/power/wakeup.c (with one
small modification) and calls either pm_suspend(), or hibernate() to
put the system into a sleep state.  If a wakeup event is reported
while the transition is in progress, it will abort the transition and
the "system suspend" work item will be queued up again.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: NeilBrown <neilb@suse.de>

1 files changed, 17 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index b464d12761ba..237c735db6c9 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -172,3 +172,20 @@ Description:
 
                 Reading from this file will display the current value, which is
                 set to 1 MB by default.
+
+What:           /sys/power/autosleep
+Date:           April 2012
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/power/autosleep file can be written one of the strings
+                returned by reads from /sys/power/state.  If that happens, a
+                work item attempting to trigger a transition of the system to
+                the sleep state represented by that string is queued up.  This
+                attempt will only succeed if there are no active wakeup sources
+                in the system at that time.  After every execution, regardless
+                of whether or not the attempt to put the system to sleep has
+                succeeded, the work item requeues itself until user space
+                writes "off" to /sys/power/autosleep.
+
+                Reading from this file causes the last string successfully
+                written to it to be returned.