hwmon: (pmbus) Add mutex to regulator ops

On PMBUS devices with multiple pages, the regulator ops need to be
protected with the update mutex. This prevents accidentally changing
the page in a separate thread while operating on the PMBUS_OPERATION
register.

Tested on Infineon xdpe11280 while a separate thread polls for sensor
data.
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Marcello Sylvester Bauer <sylv@sylv.io>
Link: https://lore.kernel.org/r/b991506bcbf665f7af185945f70bf9d5cf04637c.1645804976.git.sylv@sylv.io
Fixes: ddbb4db4 ("hwmon: (pmbus) Add regulator support")
Cc: Alan Tull <atull@opensource.altera.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/pmbus_core.c

@@ -2391,10 +2391,14 @@ static int pmbus_regulator_is_enabled(struct regulator_dev *rdev)
 {
 	struct device *dev = rdev_get_dev(rdev);
 	struct i2c_client *client = to_i2c_client(dev->parent);
+	struct pmbus_data *data = i2c_get_clientdata(client);
 	u8 page = rdev_get_id(rdev);
 	int ret;
 
+	mutex_lock(&data->update_lock);
 	ret = pmbus_read_byte_data(client, page, PMBUS_OPERATION);
+	mutex_unlock(&data->update_lock);
+
 	if (ret < 0)
 		return ret;
 
@@ -2405,11 +2409,17 @@ static int _pmbus_regulator_on_off(struct regulator_dev *rdev, bool enable)
 {
 	struct device *dev = rdev_get_dev(rdev);
 	struct i2c_client *client = to_i2c_client(dev->parent);
+	struct pmbus_data *data = i2c_get_clientdata(client);
 	u8 page = rdev_get_id(rdev);
+	int ret;
 
-	return pmbus_update_byte_data(client, page, PMBUS_OPERATION,
-				      PB_OPERATION_CONTROL_ON,
-				      enable ? PB_OPERATION_CONTROL_ON : 0);
+	mutex_lock(&data->update_lock);
+	ret = pmbus_update_byte_data(client, page, PMBUS_OPERATION,
+				     PB_OPERATION_CONTROL_ON,
+				     enable ? PB_OPERATION_CONTROL_ON : 0);
+	mutex_unlock(&data->update_lock);
+
+	return ret;
 }
 
 static int pmbus_regulator_enable(struct regulator_dev *rdev)