opp: Add dev_pm_opp_sync_regulators()

Extend OPP API with dev_pm_opp_sync_regulators() function, which syncs
voltage state of regulators.
Tested-by: Peter Geis <pgwipeout@gmail.com>
Tested-by: Nicolas Chauvet <kwizart@gmail.com>
Tested-by: Matt Merhar <mattmerhar@protonmail.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
[ Viresh: Added unlikely() ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/opp/core.c

@@ -2584,3 +2584,44 @@ void dev_pm_opp_remove_table(struct device *dev)
 	dev_pm_opp_put_opp_table(opp_table);
 }
 EXPORT_SYMBOL_GPL(dev_pm_opp_remove_table);
+
+/**
+ * dev_pm_opp_sync_regulators() - Sync state of voltage regulators
+ * @dev:	device for which we do this operation
+ *
+ * Sync voltage state of the OPP table regulators.
+ *
+ * Return: 0 on success or a negative error value.
+ */
+int dev_pm_opp_sync_regulators(struct device *dev)
+{
+	struct opp_table *opp_table;
+	struct regulator *reg;
+	int i, ret = 0;
+
+	/* Device may not have OPP table */
+	opp_table = _find_opp_table(dev);
+	if (IS_ERR(opp_table))
+		return 0;
+
+	/* Regulator may not be required for the device */
+	if (unlikely(!opp_table->regulators))
+		goto put_table;
+
+	/* Nothing to sync if voltage wasn't changed */
+	if (!opp_table->enabled)
+		goto put_table;
+
+	for (i = 0; i < opp_table->regulator_count; i++) {
+		reg = opp_table->regulators[i];
+		ret = regulator_sync_voltage(reg);
+		if (ret)
+			break;
+	}
+put_table:
+	/* Drop reference taken by _find_opp_table() */
+	dev_pm_opp_put_opp_table(opp_table);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dev_pm_opp_sync_regulators);

include/linux/pm_opp.h

@@ -161,6 +161,7 @@ int dev_pm_opp_set_sharing_cpus(struct device *cpu_dev, const struct cpumask *cp
 int dev_pm_opp_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask);
 void dev_pm_opp_remove_table(struct device *dev);
 void dev_pm_opp_cpumask_remove_table(const struct cpumask *cpumask);
+int dev_pm_opp_sync_regulators(struct device *dev);
 #else
 static inline struct opp_table *dev_pm_opp_get_opp_table(struct device *dev)
 {
@@ -384,6 +385,11 @@ static inline void dev_pm_opp_cpumask_remove_table(const struct cpumask *cpumask
 {
 }
 
+static inline int dev_pm_opp_sync_regulators(struct device *dev)
+{
+	return -ENOTSUPP;
+}
+
 #endif		/* CONFIG_PM_OPP */
 
 #if defined(CONFIG_PM_OPP) && defined(CONFIG_OF)