2 files changed, 42 insertions, 0 deletions

diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
index b23de185cb04..434a6c011675 100644
--- a/drivers/base/power/opp.c
+++ b/drivers/base/power/opp.c
@@ -73,6 +73,7 @@ struct opp {
  *              RCU usage: nodes are not modified in the list of device_opp,
  *              however addition is possible and is secured by dev_opp_list_lock
  * @dev:        device pointer
+ * @head:       notifier head to notify the OPP availability changes.
  * @opp_list:   list of opps
  *
  * This is an internal data structure maintaining the link to opps attached to
@@ -83,6 +84,7 @@ struct device_opp {
         struct list_head node;
 
         struct device *dev;
+        struct srcu_notifier_head head;
         struct list_head opp_list;
 };
 
@@ -404,6 +406,7 @@ int opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
                 }
 
                 dev_opp->dev = dev;
+                srcu_init_notifier_head(&dev_opp->head);
                 INIT_LIST_HEAD(&dev_opp->opp_list);
 
                 /* Secure the device list modification */
@@ -428,6 +431,11 @@ int opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
         list_add_rcu(&new_opp->node, head);
         mutex_unlock(&dev_opp_list_lock);
 
+        /*
+         * Notify the changes in the availability of the operable
+         * frequency/voltage list.
+         */
+        srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ADD, new_opp);
         return 0;
 }
 
@@ -504,6 +512,14 @@ static int opp_set_availability(struct device *dev, unsigned long freq,
         mutex_unlock(&dev_opp_list_lock);
         synchronize_rcu();
 
+        /* Notify the change of the OPP availability */
+        if (availability_req)
+                srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ENABLE,
+                                         new_opp);
+        else
+                srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_DISABLE,
+                                         new_opp);
+
         /* clean up old opp */
         new_opp = opp;
         goto out;
@@ -643,3 +659,17 @@ void opp_free_cpufreq_table(struct device *dev,
         *table = NULL;
 }
 #endif          /* CONFIG_CPU_FREQ */
+
+/**
+ * opp_get_notifier() - find notifier_head of the device with opp
+ * @dev:        device pointer used to lookup device OPPs.
+ */
+struct srcu_notifier_head *opp_get_notifier(struct device *dev)
+{
+        struct device_opp *dev_opp = find_device_opp(dev);
+
+        if (IS_ERR(dev_opp))
+                return ERR_PTR(PTR_ERR(dev_opp)); /* matching type */
+
+        return &dev_opp->head;
+}
diff --git a/include/linux/opp.h b/include/linux/opp.h
index 7020e9736fc5..87a9208f8aec 100644
--- a/include/linux/opp.h
+++ b/include/linux/opp.h
@@ -16,9 +16,14 @@
 
 #include <linux/err.h>
 #include <linux/cpufreq.h>
+#include <linux/notifier.h>
 
 struct opp;
 
+enum opp_event {
+        OPP_EVENT_ADD, OPP_EVENT_ENABLE, OPP_EVENT_DISABLE,
+};
+
 #if defined(CONFIG_PM_OPP)
 
 unsigned long opp_get_voltage(struct opp *opp);
@@ -40,6 +45,8 @@ int opp_enable(struct device *dev, unsigned long freq);
 
 int opp_disable(struct device *dev, unsigned long freq);
 
+struct srcu_notifier_head *opp_get_notifier(struct device *dev);
+
 #else
 static inline unsigned long opp_get_voltage(struct opp *opp)
 {
@@ -89,6 +96,11 @@ static inline int opp_disable(struct device *dev, unsigned long freq)
 {
         return 0;
 }
+
+struct srcu_notifier_head *opp_get_notifier(struct device *dev)
+{
+        return ERR_PTR(-EINVAL);
+}
 #endif          /* CONFIG_PM */
 
 #if defined(CONFIG_CPU_FREQ) && defined(CONFIG_PM_OPP)