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>

1 files changed, 36 insertions, 9 deletions

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 6958a5cd2fd8..e03600547b98 100644
--- a/drivers/opp/core.c
+++ b/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;