PM: domains: Make set_performance_state() callback optional

Make set_performance_state() callback optional in order to remove the
need from power domain drivers to implement a dummy callback. If callback
isn't implemented by a GENPD driver, then the performance state is passed
to the parent domain.
Tested-by: Peter Geis <pgwipeout@gmail.com>
Tested-by: Nicolas Chauvet <kwizart@gmail.com>
Tested-by: Matt Merhar <mattmerhar@protonmail.com>
[tested on NVIDIA Tegra20/30/124 SoCs]
Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/domain.c

@@ -297,6 +297,18 @@ static int _genpd_reeval_performance_state(struct generic_pm_domain *genpd,
 	return state;
 }
 
+static int genpd_xlate_performance_state(struct generic_pm_domain *genpd,
+					 struct generic_pm_domain *parent,
+					 unsigned int pstate)
+{
+	if (!parent->set_performance_state)
+		return pstate;
+
+	return dev_pm_opp_xlate_performance_state(genpd->opp_table,
+						  parent->opp_table,
+						  pstate);
+}
+
 static int _genpd_set_performance_state(struct generic_pm_domain *genpd,
 					unsigned int state, int depth)
 {
@@ -311,13 +323,8 @@ static int _genpd_set_performance_state(struct generic_pm_domain *genpd,
 	list_for_each_entry(link, &genpd->child_links, child_node) {
 		parent = link->parent;
 
-		if (!parent->set_performance_state)
-			continue;
-
 		/* Find parent's performance state */
-		ret = dev_pm_opp_xlate_performance_state(genpd->opp_table,
-							 parent->opp_table,
-							 state);
+		ret = genpd_xlate_performance_state(genpd, parent, state);
 		if (unlikely(ret < 0))
 			goto err;
 
@@ -339,9 +346,11 @@ static int _genpd_set_performance_state(struct generic_pm_domain *genpd,
 			goto err;
 	}
 
-	ret = genpd->set_performance_state(genpd, state);
-	if (ret)
-		goto err;
+	if (genpd->set_performance_state) {
+		ret = genpd->set_performance_state(genpd, state);
+		if (ret)
+			goto err;
+	}
 
 	genpd->performance_state = state;
 	return 0;
@@ -352,9 +361,6 @@ static int _genpd_set_performance_state(struct generic_pm_domain *genpd,
 					     child_node) {
 		parent = link->parent;
 
-		if (!parent->set_performance_state)
-			continue;
-
 		genpd_lock_nested(parent, depth + 1);
 
 		parent_state = link->prev_performance_state;
@@ -399,9 +405,6 @@ int dev_pm_genpd_set_performance_state(struct device *dev, unsigned int state)
 	if (!genpd)
 		return -ENODEV;
 
-	if (unlikely(!genpd->set_performance_state))
-		return -EINVAL;
-
 	if (WARN_ON(!dev->power.subsys_data ||
 		     !dev->power.subsys_data->domain_data))
 		return -EINVAL;