OPP: Don't return 0 on error from of_get_required_opp_performance_state()

of_get_required_opp_performance_state() returns 0 on errors currently
and a positive performance state otherwise. Since 0 is a valid
performance state (representing off), it would be better if this routine
returns negative values on error.

That will also make it behave similar to
dev_pm_opp_xlate_performance_state(), which also returns performance
states and returns negative values on error. Change the return type of
the function to "int" in order to return negative values.

This doesn't have any users for now and so no other part of the kernel
will be impacted with this change.
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/opp/of.c

@@ -983,19 +983,19 @@ EXPORT_SYMBOL_GPL(dev_pm_opp_of_get_sharing_cpus);
  * Returns the performance state of the OPP pointed out by the "required-opps"
  * property at @index in @np.
  *
- * Return: Positive performance state on success, otherwise 0 on errors.
+ * Return: Zero or positive performance state on success, otherwise negative
+ * value on errors.
  */
-unsigned int of_get_required_opp_performance_state(struct device_node *np,
-						   int index)
+int of_get_required_opp_performance_state(struct device_node *np, int index)
 {
 	struct dev_pm_opp *opp;
 	struct device_node *required_np;
 	struct opp_table *opp_table;
-	unsigned int pstate = 0;
+	int pstate = -EINVAL;
 
 	required_np = of_parse_required_opp(np, index);
 	if (!required_np)
-		return 0;
+		return -EINVAL;
 
 	opp_table = _find_table_of_opp_np(required_np);
 	if (IS_ERR(opp_table)) {

include/linux/pm_opp.h

@@ -321,7 +321,7 @@ void dev_pm_opp_of_cpumask_remove_table(const struct cpumask *cpumask);
 int dev_pm_opp_of_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask);
 struct device_node *dev_pm_opp_of_get_opp_desc_node(struct device *dev);
 struct device_node *dev_pm_opp_get_of_node(struct dev_pm_opp *opp);
-unsigned int of_get_required_opp_performance_state(struct device_node *np, int index);
+int of_get_required_opp_performance_state(struct device_node *np, int index);
 #else
 static inline int dev_pm_opp_of_add_table(struct device *dev)
 {
@@ -360,9 +360,9 @@ static inline struct device_node *dev_pm_opp_get_of_node(struct dev_pm_opp *opp)
 {
 	return NULL;
 }
-static inline unsigned int of_get_required_opp_performance_state(struct device_node *np, int index)
+static inline int of_get_required_opp_performance_state(struct device_node *np, int index)
 {
-	return 0;
+	return -ENOTSUPP;
 }
 #endif