Add dev_pm_opp_set_voltage() which allows OPP table users to set voltage
in accordance to a given OPP. In particular this is needed for driving
voltage of a generic power domain which uses OPPs and doesn't have a
clock.

Tested-by: Peter Geis <pgwipe...@gmail.com>
Tested-by: Nicolas Chauvet <kwiz...@gmail.com>
Tested-by: Matt Merhar <mattmer...@protonmail.com>
Signed-off-by: Dmitry Osipenko <dig...@gmail.com>
---
 drivers/opp/core.c     | 55 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm_opp.h |  6 +++++
 2 files changed, 61 insertions(+)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 99d18befc209..341484d58e6c 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -2731,3 +2731,58 @@ int dev_pm_opp_sync_regulators(struct device *dev)
        return ret;
 }
 EXPORT_SYMBOL_GPL(dev_pm_opp_sync_regulators);
+
+/**
+ * dev_pm_opp_set_voltage() - Change voltage of regulators
+ * @dev:       device for which we do this operation
+ * @opp:       opp based on which the voltages are to be configured
+ *
+ * Change voltage of the OPP table regulators.
+ *
+ * Return: 0 on success or a negative error value.
+ */
+int dev_pm_opp_set_voltage(struct device *dev, struct dev_pm_opp *opp)
+{
+       struct opp_table *opp_table;
+       struct regulator *reg;
+       int 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 (!opp_table->regulators)
+               goto put_table;
+
+       /* This function only supports single regulator per device */
+       if (WARN_ON(opp_table->regulator_count > 1)) {
+               dev_err(dev, "multiple regulators are not supported\n");
+               ret = -EINVAL;
+               goto put_table;
+       }
+
+       mutex_lock(&opp_table->lock);
+
+       reg = opp_table->regulators[0];
+       ret = _set_opp_voltage(dev, reg, opp->supplies);
+
+       if (!opp_table->enabled) {
+               ret = regulator_enable(reg);
+               if (ret < 0) {
+                       dev_warn(dev, "Failed to enable regulator: %d", ret);
+                       goto unlock;
+               }
+
+               opp_table->enabled = true;
+       }
+unlock:
+       mutex_unlock(&opp_table->lock);
+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_set_voltage);
diff --git a/include/linux/pm_opp.h b/include/linux/pm_opp.h
index 1c3a09cc8dcd..f344be844bde 100644
--- a/include/linux/pm_opp.h
+++ b/include/linux/pm_opp.h
@@ -163,6 +163,7 @@ 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);
+int dev_pm_opp_set_voltage(struct device *dev, struct dev_pm_opp *opp);
 #else
 static inline struct opp_table *dev_pm_opp_get_opp_table(struct device *dev)
 {
@@ -404,6 +405,11 @@ static inline int dev_pm_opp_sync_regulators(struct device 
*dev)
        return -ENOTSUPP;
 }
 
+static inline int dev_pm_opp_set_voltage(struct device *dev, struct dev_pm_opp 
*opp)
+{
+       return -ENOTSUPP;
+}
+
 #endif         /* CONFIG_PM_OPP */
 
 #if defined(CONFIG_PM_OPP) && defined(CONFIG_OF)
-- 
2.29.2

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