[PATCH] PM / runtime: Add new helper for conditional usage count incrementation

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Introduce a new runtime PM function, pm_runtime_get_if_in_use(),
that will increment the device's runtime PM usage counter and
return 'true' if its status is RPM_ACTIVE and its usage counter
is greater than 0 at the same time ('false' will be returned
otherwise).

This is useful for things that should only be done if the device
is active (from the runtime PM perspective) and used by somebody
(as indicated by the usage counter) already and they are not worth
bothering otherwise.

Requested-by: Imre Deak <imre.deak@intel.com>
Acked-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 Documentation/power/runtime_pm.txt |    5 +++++
 drivers/base/power/runtime.c       |   21 +++++++++++++++++++++
 include/linux/pm_runtime.h         |    5 +++++
 3 files changed, 31 insertions(+)

Index: linux-pm/drivers/base/power/runtime.c
===================================================================
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -966,6 +966,27 @@ int __pm_runtime_resume(struct device *d
 EXPORT_SYMBOL_GPL(__pm_runtime_resume);
 
 /**
+ * pm_runtime_get_if_in_use - Conditionally bump up the device's usage counter.
+ * @dev: Device to handle.
+ *
+ * Increment the device's runtime PM usage counter and return 'true' if its
+ * runtime PM status is RPM_ACTIVE and its usage counter is already different
+ * from zero at the same time.  Otherwise, return 'false'.
+ */
+bool pm_runtime_get_if_in_use(struct device *dev)
+{
+	unsigned long flags;
+	bool retval;
+
+	spin_lock_irqsave(&dev->power.lock, flags);
+	retval = dev->power.runtime_status == RPM_ACTIVE
+		&& atomic_inc_not_zero(&dev->power.usage_count);
+	spin_unlock_irqrestore(&dev->power.lock, flags);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(pm_runtime_get_if_in_use);
+
+/**
  * __pm_runtime_set_status - Set runtime PM status of a device.
  * @dev: Device to handle.
  * @status: New runtime PM status of the device.
Index: linux-pm/include/linux/pm_runtime.h
===================================================================
--- linux-pm.orig/include/linux/pm_runtime.h
+++ linux-pm/include/linux/pm_runtime.h
@@ -39,6 +39,7 @@ extern int pm_runtime_force_resume(struc
 extern int __pm_runtime_idle(struct device *dev, int rpmflags);
 extern int __pm_runtime_suspend(struct device *dev, int rpmflags);
 extern int __pm_runtime_resume(struct device *dev, int rpmflags);
+extern bool pm_runtime_get_if_in_use(struct device *dev);
 extern int pm_schedule_suspend(struct device *dev, unsigned int delay);
 extern int __pm_runtime_set_status(struct device *dev, unsigned int status);
 extern int pm_runtime_barrier(struct device *dev);
@@ -143,6 +144,10 @@ static inline int pm_schedule_suspend(st
 {
 	return -ENOSYS;
 }
+static inline bool pm_runtime_get_if_in_use(struct device *dev)
+{
+	return true;
+}
 static inline int __pm_runtime_set_status(struct device *dev,
 					    unsigned int status) { return 0; }
 static inline int pm_runtime_barrier(struct device *dev) { return 0; }
Index: linux-pm/Documentation/power/runtime_pm.txt
===================================================================
--- linux-pm.orig/Documentation/power/runtime_pm.txt
+++ linux-pm/Documentation/power/runtime_pm.txt
@@ -371,6 +371,11 @@ drivers/base/power/runtime.c and include
     - increment the device's usage counter, run pm_runtime_resume(dev) and
       return its result
 
+  bool pm_runtime_get_if_in_use(struct device *dev);
+    - increment the device's usage counter and return 'true' if its runtime PM
+      status is 'active' and its usage counter is greater than 0 at the same
+      time; return 'false' otherwise
+
   void pm_runtime_put_noidle(struct device *dev);
     - decrement the device's usage counter