pmdomain: core: Scale down parent/child performance states in reverse order

Power domains might have parent domains assigned that are automatically
managed by the PM domain core. In particular, parent domains are
automatically powered on/off and setting performance states on child
domains are propagated to parent domains (e.g. using an OPP table from the
device tree).

Currently the parent performance state is always adjusted before the
performance state of the child domain, which is a problem for some cases
when scaling down the performance state. More exactly, it may lead to that
the parent domain could run in a lower performance state, than what is
required by the child domain.

To fix the behaviour, let's differentiate between scaling up/down and
adjust the order of operations:

 - When scaling up, parent domains should be adjusted before the child
   domain. In case of an error, the rollback happens in reverse order.

 - When scaling down, parent domains should be adjusted after the child
   domain, in reverse order, just as if we would rollback scaling up.
   In case of an error, the rollback happens in normal order (just as
   if we would normally scale up).

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20240103-genpd-perf-order-v2-1-eeecfc55624b@gerhold.net
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: stephan-gh

drivers/pmdomain/core.c

@@ -311,72 +311,102 @@ static int genpd_xlate_performance_state(struct generic_pm_domain *genpd,
 }
 
 static int _genpd_set_performance_state(struct generic_pm_domain *genpd,
-					unsigned int state, int depth)
+					unsigned int state, int depth);
+
+static void _genpd_rollback_parent_state(struct gpd_link *link, int depth)
 {
-	struct generic_pm_domain *parent;
-	struct gpd_link *link;
-	int parent_state, ret;
+	struct generic_pm_domain *parent = link->parent;
+	int parent_state;
 
-	if (state == genpd->performance_state)
-		return 0;
+	genpd_lock_nested(parent, depth + 1);
 
-	/* Propagate to parents of genpd */
-	list_for_each_entry(link, &genpd->child_links, child_node) {
-		parent = link->parent;
+	parent_state = link->prev_performance_state;
+	link->performance_state = parent_state;
 
-		/* Find parent's performance state */
-		ret = genpd_xlate_performance_state(genpd, parent, state);
-		if (unlikely(ret < 0))
-			goto err;
+	parent_state = _genpd_reeval_performance_state(parent, parent_state);
+	if (_genpd_set_performance_state(parent, parent_state, depth + 1)) {
+		pr_err("%s: Failed to roll back to %d performance state\n",
+		       parent->name, parent_state);
+	}
 
-		parent_state = ret;
+	genpd_unlock(parent);
+}
 
-		genpd_lock_nested(parent, depth + 1);
+static int _genpd_set_parent_state(struct generic_pm_domain *genpd,
+				   struct gpd_link *link,
+				   unsigned int state, int depth)
+{
+	struct generic_pm_domain *parent = link->parent;
+	int parent_state, ret;
 
-		link->prev_performance_state = link->performance_state;
-		link->performance_state = parent_state;
-		parent_state = _genpd_reeval_performance_state(parent,
-						parent_state);
-		ret = _genpd_set_performance_state(parent, parent_state, depth + 1);
-		if (ret)
-			link->performance_state = link->prev_performance_state;
+	/* Find parent's performance state */
+	ret = genpd_xlate_performance_state(genpd, parent, state);
+	if (unlikely(ret < 0))
+		return ret;
 
-		genpd_unlock(parent);
+	parent_state = ret;
 
-		if (ret)
-			goto err;
-	}
+	genpd_lock_nested(parent, depth + 1);
 
-	if (genpd->set_performance_state) {
-		ret = genpd->set_performance_state(genpd, state);
-		if (ret)
-			goto err;
-	}
+	link->prev_performance_state = link->performance_state;
+	link->performance_state = parent_state;
 
-	genpd->performance_state = state;
-	return 0;
+	parent_state = _genpd_reeval_performance_state(parent, parent_state);
+	ret = _genpd_set_performance_state(parent, parent_state, depth + 1);
+	if (ret)
+		link->performance_state = link->prev_performance_state;
 
-err:
-	/* Encountered an error, lets rollback */
-	list_for_each_entry_continue_reverse(link, &genpd->child_links,
-					     child_node) {
-		parent = link->parent;
+	genpd_unlock(parent);
 
-		genpd_lock_nested(parent, depth + 1);
+	return ret;
+}
+
+static int _genpd_set_performance_state(struct generic_pm_domain *genpd,
+					unsigned int state, int depth)
+{
+	struct gpd_link *link = NULL;
+	int ret;
+
+	if (state == genpd->performance_state)
+		return 0;
 
-		parent_state = link->prev_performance_state;
-		link->performance_state = parent_state;
+	/* When scaling up, propagate to parents first in normal order */
+	if (state > genpd->performance_state) {
+		list_for_each_entry(link, &genpd->child_links, child_node) {
+			ret = _genpd_set_parent_state(genpd, link, state, depth);
+			if (ret)
+				goto rollback_parents_up;
+		}
+	}
 
-		parent_state = _genpd_reeval_performance_state(parent,
-						parent_state);
-		if (_genpd_set_performance_state(parent, parent_state, depth + 1)) {
-			pr_err("%s: Failed to roll back to %d performance state\n",
-			       parent->name, parent_state);
+	if (genpd->set_performance_state) {
+		ret = genpd->set_performance_state(genpd, state);
+		if (ret) {
+			if (link)
+				goto rollback_parents_up;
+			return ret;
 		}
+	}
 
-		genpd_unlock(parent);
+	/* When scaling down, propagate to parents last in reverse order */
+	if (state < genpd->performance_state) {
+		list_for_each_entry_reverse(link, &genpd->child_links, child_node) {
+			ret = _genpd_set_parent_state(genpd, link, state, depth);
+			if (ret)
+				goto rollback_parents_down;
+		}
 	}
 
+	genpd->performance_state = state;
+	return 0;
+
+rollback_parents_up:
+	list_for_each_entry_continue_reverse(link, &genpd->child_links, child_node)
+		_genpd_rollback_parent_state(link, depth);
+	return ret;
+rollback_parents_down:
+	list_for_each_entry_continue(link, &genpd->child_links, child_node)
+		_genpd_rollback_parent_state(link, depth);
 	return ret;
 }