[PATCH] opp: Allow lazy-linking of required-opps

[Viresh Kumar]

The OPP core currently requires the required opp tables to be available
before the dependent OPP table is added, as it needs to create links
from the dependent OPP table to the required ones. This may not be
convenient to all the platforms though, as this requires strict ordering
of probing of drivers.

This patch allows lazy-linking of the required-opps. The OPP tables for
which the required-opp-tables aren't available at the time of their
initialization, are added to a special list of OPP tables:
pending_opp_tables. Later on, whenever a new OPP table is registered
with the OPP core, we check if it is required by an OPP table in the
pending list; if yes, then we complete the linking then and there.

An OPP table is marked unusable until the time all its required-opp
tables are available. And if lazy-linking fails for an OPP table, the
OPP core disables all of its OPPs to make sure no one can use them.

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
 drivers/opp/core.c |  13 ++++++
 drivers/opp/of.c   | 113 +++++++++++++++++++++++++++++++++++++++++++--
 drivers/opp/opp.h  |   4 +-
 3 files changed, 124 insertions(+), 6 deletions(-)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index ba43e6a3dc0a..cafd468443a6 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -27,6 +27,10 @@
  * various states of availability.
  */
 LIST_HEAD(opp_tables);
+
+/* The root of the list of opp-tables that aren't fully initialized yet */
+LIST_HEAD(pending_opp_tables);
+
 /* Lock to allow exclusive modification to the device and opp lists */
 DEFINE_MUTEX(opp_table_lock);
 
@@ -754,6 +758,10 @@ static int _set_required_opps(struct device *dev,
 	if (!required_opp_tables)
 		return 0;
 
+	/* required-opps not fully initialized yet */
+	if (!list_empty(&opp_table->pending))
+		return -EBUSY;
+
 	/* Single genpd case */
 	if (!genpd_virt_devs) {
 		pstate = likely(opp) ? opp->required_opps[0]->pstate : 0;
@@ -964,6 +972,7 @@ static struct opp_table *_allocate_opp_table(struct device *dev, int index)
 	mutex_init(&opp_table->lock);
 	mutex_init(&opp_table->genpd_virt_dev_lock);
 	INIT_LIST_HEAD(&opp_table->dev_list);
+	INIT_LIST_HEAD(&opp_table->pending);
 
 	/* Mark regulator count uninitialized */
 	opp_table->regulator_count = -1;
@@ -1946,6 +1955,10 @@ int dev_pm_opp_xlate_performance_state(struct opp_table *src_table,
 	if (!pstate)
 		return 0;
 
+	/* required-opps not fully initialized yet */
+	if (!list_empty(&src_table->pending))
+		return -EBUSY;
+
 	/*
 	 * Normally the src_table will have the "required_opps" property set to
 	 * point to one of the OPPs in the dst_table, but in some cases the
diff --git a/drivers/opp/of.c b/drivers/opp/of.c
index 9cd8f0adacae..a17bb47c39a5 100644
--- a/drivers/opp/of.c
+++ b/drivers/opp/of.c
@@ -143,7 +143,7 @@ static void _opp_table_free_required_tables(struct opp_table *opp_table)
 
 	for (i = 0; i < opp_table->required_opp_count; i++) {
 		if (IS_ERR_OR_NULL(required_opp_tables[i]))
-			break;
+			continue;
 
 		dev_pm_opp_put_opp_table(required_opp_tables[i]);
 	}
@@ -152,6 +152,7 @@ static void _opp_table_free_required_tables(struct opp_table *opp_table)
 
 	opp_table->required_opp_count = 0;
 	opp_table->required_opp_tables = NULL;
+	list_del(&opp_table->pending);
 }
 
 /*
@@ -164,6 +165,7 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
 {
 	struct opp_table **required_opp_tables;
 	struct device_node *required_np, *np;
+	bool pending = false;
 	int count, i;
 
 	/* Traversing the first OPP node is all we need */
@@ -193,8 +195,10 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
 		required_opp_tables[i] = _find_table_of_opp_np(required_np);
 		of_node_put(required_np);
 
-		if (IS_ERR(required_opp_tables[i]))
-			goto free_required_tables;
+		if (IS_ERR(required_opp_tables[i])) {
+			pending = true;
+			continue;
+		}
 
 		/*
 		 * We only support genpd's OPPs in the "required-opps" for now,
@@ -208,6 +212,10 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
 		}
 	}
 
+	/* Let's do the linking later on */
+	if (pending)
+		list_add(&opp_table->pending, &pending_opp_tables);
+
 	goto put_np;
 
 free_required_tables:
@@ -276,7 +284,7 @@ void _of_opp_free_required_opps(struct opp_table *opp_table,
 
 	for (i = 0; i < opp_table->required_opp_count; i++) {
 		if (!required_opps[i])
-			break;
+			continue;
 
 		/* Put the reference back */
 		dev_pm_opp_put(required_opps[i]);
@@ -307,6 +315,10 @@ static int _of_opp_alloc_required_opps(struct opp_table *opp_table,
 	for (i = 0; i < count; i++) {
 		required_table = opp_table->required_opp_tables[i];
 
+		/* Required table not added yet, we will link later */
+		if (IS_ERR_OR_NULL(required_table))
+			continue;
+
 		np = of_parse_required_opp(opp->np, i);
 		if (unlikely(!np)) {
 			ret = -ENODEV;
@@ -332,6 +344,97 @@ static int _of_opp_alloc_required_opps(struct opp_table *opp_table,
 	return ret;
 }
 
+static int lazy_link_required_opps(struct opp_table *opp_table,
+				   struct opp_table *required_opp_table,
+				   int index)
+{
+	struct device_node *required_np;
+	struct dev_pm_opp *opp;
+
+	list_for_each_entry(opp, &opp_table->opp_list, node) {
+		required_np = of_parse_required_opp(opp->np, index);
+		if (unlikely(!required_np))
+			return -ENODEV;
+
+		opp->required_opps[index] = _find_opp_of_np(required_opp_table, required_np);
+		of_node_put(required_np);
+
+		if (!opp->required_opps[index]) {
+			pr_err("%s: Unable to find required OPP node: %pOF (%d)\n",
+					__func__, opp->np, index);
+			return -ENODEV;
+		}
+	}
+
+	return 0;
+}
+
+static void lazy_link_required_opp_table(struct opp_table *required_opp_table)
+{
+	struct opp_table *opp_table, *temp, **required_opp_tables;
+	struct device_node *required_np, *opp_np, *required_table_np;
+	int i, ret;
+
+	/*
+	 * We only support genpd's OPPs in the "required-opps" for now,
+	 * as we don't know much about other cases.
+	 */
+	if (!required_opp_table->is_genpd)
+		return;
+
+	mutex_lock(&opp_table_lock);
+
+	list_for_each_entry_safe(opp_table, temp, &pending_opp_tables, pending) {
+		bool pending = false;
+
+		/* opp_np can't be invalid here */
+		opp_np = of_get_next_available_child(opp_table->np, NULL);
+
+		for (i = 0; i < opp_table->required_opp_count; i++) {
+			required_opp_tables = opp_table->required_opp_tables;
+
+			if (!IS_ERR_OR_NULL(required_opp_tables[i]))
+				continue;
+
+			/* required_np can't be invalid here */
+			required_np = of_parse_required_opp(opp_np, i);
+			required_table_np = of_get_parent(required_np);
+
+			of_node_put(required_table_np);
+			of_node_put(required_np);
+
+			if (required_table_np != required_opp_table->np) {
+				pending = true;
+				continue;
+			}
+
+			required_opp_tables[i] = required_opp_table;
+			_get_opp_table_kref(required_opp_table);
+
+			/* Link OPPs now */
+			ret = lazy_link_required_opps(opp_table, required_opp_table, i);
+			if (ret) {
+				struct dev_pm_opp *opp;
+
+				/* Mark OPPs unusable on error */
+				list_for_each_entry(opp, &opp_table->opp_list, node)
+					opp->available = false;
+				break;
+			}
+		}
+
+		of_node_put(opp_np);
+
+		/* All required opp-tables found, remove from pending list */
+		if (!pending) {
+			list_del(&opp_table->pending);
+			INIT_LIST_HEAD(&opp_table->pending);
+		}
+	}
+
+	mutex_unlock(&opp_table_lock);
+}
+
 static bool _opp_is_supported(struct device *dev, struct opp_table *opp_table,
 			      struct device_node *np)
 {
@@ -702,6 +805,8 @@ static int _of_add_opp_table_v2(struct device *dev, struct opp_table *opp_table)
 	if (pstate_count)
 		opp_table->genpd_performance_state = true;
 
+	lazy_link_required_opp_table(opp_table);
+
 	return 0;
 
 remove_static_opp:
diff --git a/drivers/opp/opp.h b/drivers/opp/opp.h
index d14e27102730..1acbea35d58e 100644
--- a/drivers/opp/opp.h
+++ b/drivers/opp/opp.h
@@ -25,7 +25,7 @@ struct regulator;
 /* Lock to allow exclusive modification to the device and opp lists */
 extern struct mutex opp_table_lock;
 
-extern struct list_head opp_tables;
+extern struct list_head opp_tables, pending_opp_tables;
 
 /*
  * Internal data structure organization with the OPP layer library is as
@@ -160,7 +160,7 @@ enum opp_table_access {
  * meant for book keeping and private to OPP library.
  */
 struct opp_table {
-	struct list_head node;
+	struct list_head node, pending;
 
 	struct blocking_notifier_head head;
 	struct list_head dev_list;
-- 
2.21.0.rc0.269.g1a574e7a288b