PM / Runtime: Implement autosuspend support

This patch (as1427) implements the "autosuspend" facility for runtime
PM.  A few new fields are added to the dev_pm_info structure and
several new PM helper functions are defined, for telling the PM core
whether or not a device uses autosuspend, for setting the autosuspend
delay, and for marking periods of device activity.

Drivers that do not want to use autosuspend can continue using the
same helper functions as before; their behavior will not change.  In
addition, drivers supporting autosuspend can also call the old helper
functions to get the old behavior.

The details are all explained in Documentation/power/runtime_pm.txt
and Documentation/ABI/testing/sysfs-devices-power.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

1 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power
index 6bb2dd3c3a71..7628cd1bc36a 100644
--- a/Documentation/ABI/testing/sysfs-devices-power
+++ b/Documentation/ABI/testing/sysfs-devices-power
@@ -147,3 +147,21 @@ Description:
                 milliseconds.  This attribute is read-only.  If the device is
                 not enabled to wake up the system from sleep states, this
                 attribute is empty.
+
+What:           /sys/devices/.../power/autosuspend_delay_ms
+Date:           September 2010
+Contact:        Alan Stern <stern@rowland.harvard.edu>
+Description:
+                The /sys/devices/.../power/autosuspend_delay_ms attribute
+                contains the autosuspend delay value (in milliseconds).  Some
+                drivers do not want their device to suspend as soon as it
+                becomes idle at run time; they want the device to remain
+                inactive for a certain minimum period of time first.  That
+                period is called the autosuspend delay.  Negative values will
+                prevent the device from being suspended at run time (similar
+                to writing "on" to the power/control attribute).  Values >=
+                1000 will cause the autosuspend timer expiration to be rounded
+                up to the nearest second.
+
+                Not all drivers support this attribute.  If it isn't supported,
+                attempts to read or write it will yield I/O errors.