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 <[e-mail]>
Signed-off-by: Viresh Kumar <[e-mail]>

drivers/opp/core.c

···
  * 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 */
···
 		pr_err("%s: Invalid parameters\n", __func__);
 		return 0;
 	}
+
+	/* required-opps not fully initialized yet */
+	if (lazy_linking_pending(opp->opp_table))
+		return 0;
 
 	return opp->required_opps[index]->pstate;
 }
···
 	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);
···
 	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;
···
 	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.
···
 	     struct opp_table *opp_table, bool rate_not_available)
 {
 	struct list_head *head;
-	unsigned int i;
 	int ret;
 
 	mutex_lock(&opp_table->lock);
···
 			 __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;
 }
···
 	 */
 	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)

drivers/opp/of.c

···
 
 	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]);
 	}
···
 
 	opp_table->required_opp_count = 0;
 	opp_table->required_opp_tables = NULL;
+	list_del(&opp_table->lazy);
 }
 
 /*
···
 {
 	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 */
···
 		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,
···
 			goto free_required_tables;
 		}
 	}
+
+	/* Let's do the linking later on */
+	if (lazy)
+		list_add(&opp_table->lazy, &lazy_opp_tables);
 
 	goto put_np;
 
···
 
 	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 */
···
 
 	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)) {
···
 	_of_opp_free_required_opps(opp_table, opp);
 
 	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)
···
 			break;
 		}
 	}
+
+	lazy_link_required_opp_table(opp_table);
 
 	return 0;
 

drivers/opp/opp.h

···
 /* 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
···
  * 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;
···
 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);