opp: Allow lazy-linking of required-opps

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 for all the platforms though, as this requires strict
ordering for probing the 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:
lazy_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.

Tested-by: Hsin-Yi Wang <hsinyi@chromium.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/opp/core.c

@@ -27,6 +27,10 @@
  * various states of availability.
  */
 LIST_HEAD(opp_tables);
+
+/* OPP tables with uninitialized required OPPs */
+LIST_HEAD(lazy_opp_tables);
+
 /* Lock to allow exclusive modification to the device and opp lists */
 DEFINE_MUTEX(opp_table_lock);
 /* Flag indicating that opp_tables list is being updated at the moment */
@@ -163,6 +167,10 @@ unsigned int dev_pm_opp_get_required_pstate(struct dev_pm_opp *opp,
 		return 0;
 	}
 
+	/* required-opps not fully initialized yet */
+	if (lazy_linking_pending(opp->opp_table))
+		return 0;
+
 	return opp->required_opps[index]->pstate;
 }
 EXPORT_SYMBOL_GPL(dev_pm_opp_get_required_pstate);
@@ -885,6 +893,10 @@ static int _set_required_opps(struct device *dev,
 	if (!required_opp_tables)
 		return 0;
 
+	/* required-opps not fully initialized yet */
+	if (lazy_linking_pending(opp_table))
+		return -EBUSY;
+
 	/* Single genpd case */
 	if (!genpd_virt_devs)
 		return _set_required_opp(dev, dev, opp, 0);
@@ -1181,6 +1193,7 @@ 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->lazy);
 
 	/* Mark regulator count uninitialized */
 	opp_table->regulator_count = -1;
@@ -1632,6 +1645,21 @@ static int _opp_is_duplicate(struct device *dev, struct dev_pm_opp *new_opp,
 	return 0;
 }
 
+void _required_opps_available(struct dev_pm_opp *opp, int count)
+{
+	int i;
+
+	for (i = 0; i < count; i++) {
+		if (opp->required_opps[i]->available)
+			continue;
+
+		opp->available = false;
+		pr_warn("%s: OPP not supported by required OPP %pOF (%lu)\n",
+			 __func__, opp->required_opps[i]->np, opp->rate);
+		return;
+	}
+}
+
 /*
  * Returns:
  * 0: On success. And appropriate error message for duplicate OPPs.
@@ -1646,7 +1674,6 @@ int _opp_add(struct device *dev, struct dev_pm_opp *new_opp,
 	     struct opp_table *opp_table, bool rate_not_available)
 {
 	struct list_head *head;
-	unsigned int i;
 	int ret;
 
 	mutex_lock(&opp_table->lock);
@@ -1672,15 +1699,11 @@ int _opp_add(struct device *dev, struct dev_pm_opp *new_opp,
 			 __func__, new_opp->rate);
 	}
 
-	for (i = 0; i < opp_table->required_opp_count; i++) {
-		if (new_opp->required_opps[i]->available)
-			continue;
+	/* required-opps not fully initialized yet */
+	if (lazy_linking_pending(opp_table))
+		return 0;
 
-		new_opp->available = false;
-		dev_warn(dev, "%s: OPP not supported by required OPP %pOF (%lu)\n",
-			 __func__, new_opp->required_opps[i]->np, new_opp->rate);
-		break;
-	}
+	_required_opps_available(new_opp, opp_table->required_opp_count);
 
 	return 0;
 }
@@ -2388,6 +2411,10 @@ int dev_pm_opp_xlate_performance_state(struct opp_table *src_table,
 	if (!src_table || !src_table->required_opp_count)
 		return pstate;
 
+	/* required-opps not fully initialized yet */
+	if (lazy_linking_pending(src_table))
+		return -EBUSY;
+
 	for (i = 0; i < src_table->required_opp_count; i++) {
 		if (src_table->required_opp_tables[i]->np == dst_table->np)
 			break;

drivers/opp/of.c

@@ -144,7 +144,7 @@ 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]);
 	}
@@ -153,6 +153,7 @@ 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->lazy);
 }
 
 /*
@@ -165,6 +166,7 @@ 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 lazy = false;
 	int count, i;
 
 	/* Traversing the first OPP node is all we need */
@@ -195,8 +197,10 @@ 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])) {
+			lazy = true;
+			continue;
+		}
 
 		/*
 		 * We only support genpd's OPPs in the "required-opps" for now,
@@ -210,6 +214,10 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
 		}
 	}
 
+	/* Let's do the linking later on */
+	if (lazy)
+		list_add(&opp_table->lazy, &lazy_opp_tables);
+
 	goto put_np;
 
 free_required_tables:
@@ -278,14 +286,14 @@ 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]);
 	}
 
-	kfree(required_opps);
 	opp->required_opps = NULL;
+	kfree(required_opps);
 }
 
 /* Populate all required OPPs which are part of "required-opps" list */
@@ -309,6 +317,10 @@ 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;
@@ -334,6 +346,104 @@ static int _of_opp_alloc_required_opps(struct opp_table *opp_table,
 	return ret;
 }
 
+/* Link required OPPs for an individual OPP */
+static int lazy_link_required_opps(struct opp_table *opp_table,
+				   struct opp_table *new_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(new_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;
+}
+
+/* Link required OPPs for all OPPs of the newly added OPP table */
+static void lazy_link_required_opp_table(struct opp_table *new_table)
+{
+	struct opp_table *opp_table, *temp, **required_opp_tables;
+	struct device_node *required_np, *opp_np, *required_table_np;
+	struct dev_pm_opp *opp;
+	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 (!new_table->is_genpd)
+		return;
+
+	mutex_lock(&opp_table_lock);
+
+	list_for_each_entry_safe(opp_table, temp, &lazy_opp_tables, lazy) {
+		bool lazy = 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;
+
+			/* Required opp-table is already parsed */
+			if (!IS_ERR(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);
+
+			/*
+			 * Newly added table isn't the required opp-table for
+			 * opp_table.
+			 */
+			if (required_table_np != new_table->np) {
+				lazy = true;
+				continue;
+			}
+
+			required_opp_tables[i] = new_table;
+			_get_opp_table_kref(new_table);
+
+			/* Link OPPs now */
+			ret = lazy_link_required_opps(opp_table, new_table, i);
+			if (ret) {
+				/* The OPPs will be marked unusable */
+				lazy = false;
+				break;
+			}
+		}
+
+		of_node_put(opp_np);
+
+		/* All required opp-tables found, remove from lazy list */
+		if (!lazy) {
+			list_del(&opp_table->lazy);
+			INIT_LIST_HEAD(&opp_table->lazy);
+
+			list_for_each_entry(opp, &opp_table->opp_list, node)
+				_required_opps_available(opp, opp_table->required_opp_count);
+		}
+	}
+
+	mutex_unlock(&opp_table_lock);
+}
+
 static int _bandwidth_supported(struct device *dev, struct opp_table *opp_table)
 {
 	struct device_node *np, *opp_np;
@@ -889,6 +999,8 @@ static int _of_add_opp_table_v2(struct device *dev, struct opp_table *opp_table)
 		}
 	}
 
+	lazy_link_required_opp_table(opp_table);
+
 	return 0;
 
 remove_static_opp:

drivers/opp/opp.h

@@ -26,7 +26,7 @@ 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, lazy_opp_tables;
 
 /*
  * Internal data structure organization with the OPP layer library is as
@@ -168,7 +168,7 @@ enum opp_table_access {
  * meant for book keeping and private to OPP library.
  */
 struct opp_table {
-	struct list_head node;
+	struct list_head node, lazy;
 
 	struct blocking_notifier_head head;
 	struct list_head dev_list;
@@ -229,6 +229,12 @@ int _opp_add_v1(struct opp_table *opp_table, struct device *dev, unsigned long f
 void _dev_pm_opp_cpumask_remove_table(const struct cpumask *cpumask, int last_cpu);
 struct opp_table *_add_opp_table_indexed(struct device *dev, int index, bool getclk);
 void _put_opp_list_kref(struct opp_table *opp_table);
+void _required_opps_available(struct dev_pm_opp *opp, int count);
+
+static inline bool lazy_linking_pending(struct opp_table *opp_table)
+{
+	return unlikely(!list_empty(&opp_table->lazy));
+}
 
 #ifdef CONFIG_OF
 void _of_init_opp_table(struct opp_table *opp_table, struct device *dev, int index);