Add dev_pm_opp_get_required_pstate() which allows OPP users to retrieve
required performance state of a given OPP.

Tested-by: Peter Geis <redacted>
Tested-by: Nicolas Chauvet <redacted>
Tested-by: Matt Merhar <redacted>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 drivers/opp/core.c     | 22 ++++++++++++++++++++++
 include/linux/pm_opp.h | 10 ++++++++++
 2 files changed, 32 insertions(+)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index df0969002555..fde2ec00ab0e 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c

@@ -145,6 +145,28 @@ unsigned int dev_pm_opp_get_level(struct dev_pm_opp *opp)
 }
 EXPORT_SYMBOL_GPL(dev_pm_opp_get_level);
 
+/**
+ * dev_pm_opp_get_required_pstate() - Gets the required performance state
+ *                                    corresponding to an available opp
+ * @opp:	opp for which performance state has to be returned for
+ * @index:	index of the required opp
+ *
+ * Return: performance state read from device tree corresponding to the
+ * required opp, else return 0.
+ */
+unsigned int dev_pm_opp_get_required_pstate(struct dev_pm_opp *opp,
+					    unsigned int index)
+{
+	if (IS_ERR_OR_NULL(opp) || !opp->available ||
+	    index >= opp->opp_table->required_opp_count) {
+		pr_err("%s: Invalid parameters\n", __func__);
+		return 0;
+	}
+
+	return opp->required_opps[index]->pstate;
+}
+EXPORT_SYMBOL_GPL(dev_pm_opp_get_required_pstate);
+
 /**
  * dev_pm_opp_is_turbo() - Returns if opp is turbo OPP or not
  * @opp: opp for which turbo mode is being verified

diff --git a/include/linux/pm_opp.h b/include/linux/pm_opp.h
index b7dc993487c7..e072148ae0e1 100644
--- a/include/linux/pm_opp.h
+++ b/include/linux/pm_opp.h

@@ -98,6 +98,9 @@ unsigned long dev_pm_opp_get_freq(struct dev_pm_opp *opp);
 
 unsigned int dev_pm_opp_get_level(struct dev_pm_opp *opp);
 
+unsigned int dev_pm_opp_get_required_pstate(struct dev_pm_opp *opp,
+					    unsigned int index);
+
 bool dev_pm_opp_is_turbo(struct dev_pm_opp *opp);
 
 int dev_pm_opp_get_opp_count(struct device *dev);

@@ -194,6 +197,13 @@ static inline unsigned int dev_pm_opp_get_level(struct dev_pm_opp *opp)
 	return 0;
 }
 
+static inline
+unsigned int dev_pm_opp_get_required_pstate(struct dev_pm_opp *opp,
+					    unsigned int index)
+{
+	return 0;
+}
+
 static inline bool dev_pm_opp_is_turbo(struct dev_pm_opp *opp)
 {
 	return false;