PM / OPP: discard duplicate OPPs

We don't have any protection against addition of duplicate OPPs currently and in
case some code tries to add them, it will end up corrupting OPP tables.

We need to handle some duplication cases separately as returning error might not
be the right thing always. The new list of return values for dev_pm_opp_add()
are:

 0:         On success OR
            Duplicate OPPs (both freq and volt are same) and opp->available
 -EEXIST:   Freq are same and volt are different OR
            Duplicate OPPs (both freq and volt are same) and !opp->available
 -ENOMEM:   Memory allocation failure
Acked-by: NNishanth Menon <nm@ti.com>
Signed-off-by: NChander Kashyap <k.chander@samsung.com>
Signed-off-by: NInderpal Singh <inderpal.s@samsung.com>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/opp.c

@@ -394,6 +394,13 @@ EXPORT_SYMBOL_GPL(dev_pm_opp_find_freq_floor);
  * to keep the integrity of the internal data structures. Callers should ensure
  * that this function is *NOT* called under RCU protection or in contexts where
  * mutex cannot be locked.
+ *
+ * Return:
+ * 0:		On success OR
+ *		Duplicate OPPs (both freq and volt are same) and opp->available
+ * -EEXIST:	Freq are same and volt are different OR
+ *		Duplicate OPPs (both freq and volt are same) and !opp->available
+ * -ENOMEM:	Memory allocation failure
  */
 int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
 {
@@ -443,15 +450,31 @@ int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
 	new_opp->u_volt = u_volt;
 	new_opp->available = true;
 
-	/* Insert new OPP in order of increasing frequency */
+	/*
+	 * Insert new OPP in order of increasing frequency
+	 * and discard if already present
+	 */
 	head = &dev_opp->opp_list;
 	list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
-		if (new_opp->rate < opp->rate)
+		if (new_opp->rate <= opp->rate)
 			break;
 		else
 			head = &opp->node;
 	}
 
+	/* Duplicate OPPs ? */
+	if (new_opp->rate == opp->rate) {
+		int ret = opp->available && new_opp->u_volt == opp->u_volt ?
+			0 : -EEXIST;
+
+		dev_warn(dev, "%s: duplicate OPPs detected. Existing: freq: %lu, volt: %lu, enabled: %d. New: freq: %lu, volt: %lu, enabled: %d\n",
+			 __func__, opp->rate, opp->u_volt, opp->available,
+			 new_opp->rate, new_opp->u_volt, new_opp->available);
+		mutex_unlock(&dev_opp_list_lock);
+		kfree(new_opp);
+		return ret;
+	}
+
 	list_add_rcu(&new_opp->node, head);
 	mutex_unlock(&dev_opp_list_lock);