cpuidle: prepare the cpuidle core to handle multiple drivers

This patch is a preparation for the multiple cpuidle drivers support.

As the next patch will introduce the multiple drivers with the Kconfig
option and we want to keep the code clean and understandable, this patch
defines a set of functions for encapsulating some common parts and splits
what should be done under a lock from the rest.

[rjw: Modified the subject and changelog slightly.]
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpuidle/driver.c

@@ -39,11 +39,20 @@ static void set_power_states(struct cpuidle_driver *drv)
 		drv->states[i].power_usage = -1 - i;
 }
 
-/**
- * cpuidle_register_driver - registers a driver
- * @drv: the driver
- */
-int cpuidle_register_driver(struct cpuidle_driver *drv)
+static void __cpuidle_driver_init(struct cpuidle_driver *drv)
+{
+	drv->refcnt = 0;
+
+	if (!drv->power_specified)
+		set_power_states(drv);
+}
+
+static void cpuidle_set_driver(struct cpuidle_driver *drv)
+{
+	cpuidle_curr_driver = drv;
+}
+
+static int __cpuidle_register_driver(struct cpuidle_driver *drv)
 {
 	if (!drv || !drv->state_count)
 		return -EINVAL;
@@ -51,22 +60,38 @@ int cpuidle_register_driver(struct cpuidle_driver *drv)
 	if (cpuidle_disabled())
 		return -ENODEV;
 
-	spin_lock(&cpuidle_driver_lock);
-	if (cpuidle_curr_driver) {
-		spin_unlock(&cpuidle_driver_lock);
+	if (cpuidle_get_driver())
 		return -EBUSY;
-	}
 
-	if (!drv->power_specified)
-		set_power_states(drv);
+	__cpuidle_driver_init(drv);
 
-	drv->refcnt = 0;
+	cpuidle_set_driver(drv);
 
-	cpuidle_curr_driver = drv;
+	return 0;
+}
+
+static void __cpuidle_unregister_driver(struct cpuidle_driver *drv)
+{
+	if (drv != cpuidle_get_driver())
+		return;
+
+	if (!WARN_ON(drv->refcnt > 0))
+		cpuidle_set_driver(NULL);
+}
 
+/**
+ * cpuidle_register_driver - registers a driver
+ * @drv: the driver
+ */
+int cpuidle_register_driver(struct cpuidle_driver *drv)
+{
+	int ret;
+
+	spin_lock(&cpuidle_driver_lock);
+	ret = __cpuidle_register_driver(drv);
 	spin_unlock(&cpuidle_driver_lock);
 
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(cpuidle_register_driver);
 
@@ -86,8 +111,7 @@ EXPORT_SYMBOL_GPL(cpuidle_get_driver);
 void cpuidle_unregister_driver(struct cpuidle_driver *drv)
 {
 	spin_lock(&cpuidle_driver_lock);
-	if (drv == cpuidle_curr_driver && !WARN_ON(drv->refcnt > 0))
-		cpuidle_curr_driver = NULL;
+	__cpuidle_unregister_driver(drv);
 	spin_unlock(&cpuidle_driver_lock);
 }
 EXPORT_SYMBOL_GPL(cpuidle_unregister_driver);
@@ -98,7 +122,7 @@ struct cpuidle_driver *cpuidle_driver_ref(void)
 
 	spin_lock(&cpuidle_driver_lock);
 
-	drv = cpuidle_curr_driver;
+	drv = cpuidle_get_driver();
 	drv->refcnt++;
 
 	spin_unlock(&cpuidle_driver_lock);
@@ -107,7 +131,7 @@ struct cpuidle_driver *cpuidle_driver_ref(void)
 
 void cpuidle_driver_unref(void)
 {
-	struct cpuidle_driver *drv = cpuidle_curr_driver;
+	struct cpuidle_driver *drv = cpuidle_get_driver();
 
 	spin_lock(&cpuidle_driver_lock);