[PATCH 2/2] PM / Runtime: Document power.runtime_auto and related functions

From: Rafael J. Wysocki
Date: Wed Jan 27 2010 - 18:11:39 EST

From: Rafael J. Wysocki <rjw@xxxxxxx>

The power.runtime_auto device flag and the helper functions
pm_runtime_allow() and pm_runtime_forbid() used to modify it are a
part of the run-time power management framework and therefore they
should be described in Documentation/power/runtime_pm.txt.

Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
Documentation/power/runtime_pm.txt | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)

Index: linux-2.6/Documentation/power/runtime_pm.txt
--- linux-2.6.orig/Documentation/power/runtime_pm.txt
+++ linux-2.6/Documentation/power/runtime_pm.txt
@@ -224,6 +224,12 @@ defined in include/linux/pm.h:
RPM_SUSPENDED, which means that each device is initially regarded by the
PM core as 'suspended', regardless of its real hardware status

+ unsigned int runtime_auto;
+ - if set, indicates that the user space has allowed the device driver to
+ power manage the device at run time via the /sys/devices/.../power/control
+ interface; it may only be modified with the help of the pm_runtime_allow()
+ and pm_runtime_forbid() helper functions
All of the above fields are members of the 'power' member of 'struct device'.

4. Run-time PM Device Helper Functions
@@ -329,6 +335,16 @@ drivers/base/power/runtime.c and include
'power.runtime_error' is set or 'power.disable_depth' is greater than

+ void pm_runtime_allow(struct device *dev);
+ - set the power.runtime_auto flag for the device and decrease its usage
+ counter (used by the /sys/devices/.../power/control interface to
+ effectively allow the device to be power managed at run time)
+ void pm_runtime_forbid(struct device *dev);
+ - unset the power.runtime_auto flag for the device and increase its usage
+ counter (used by the /sys/devices/.../power/control interface to
+ effectively prevent the device from being power managed at run time)
It is safe to execute the following helper functions from interrupt context:

@@ -382,6 +398,18 @@ may be desirable to suspend the device a
finished, so the PM core uses pm_runtime_idle_sync() to invoke the
subsystem-level idle callback for the device at that time.

+The user space can effectively disallow the driver of the device to power manage
+it at run time by changing the value of its /sys/devices/.../power/control
+attribute to "on", which causes pm_runtime_forbid() to be called. In principle,
+this mechanism may also be used by the driver to effectively turn off the
+run-time power management of the device until the user space turns it on.
+Namely, during the initialization the driver can make sure that the run-time PM
+status of the device is 'active' and call pm_runtime_forbid(). It should be
+noted, however, that if the user space has already intentionally changed the
+value of /sys/devices/.../power/control to "auto" to allow the driver to power
+manage the device at run time, the driver may confuse it by using
+pm_runtime_forbid() this way.
6. Run-time PM and System Sleep

Run-time PM and system sleep (i.e., system suspend and hibernation, also known

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