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, 8 insertions, 2 deletions

diff --git a/drivers/opp/opp.h b/drivers/opp/opp.h
index 372df68e185b..9b9daf83b074 100644
--- a/drivers/opp/opp.h
+++ b/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);