iio: addac: ad74115: Use devm_regulator_get_enable_read_voltage()

We can reduce boilerplate code by using
devm_regulator_get_enable_read_voltage().

To maintain backwards compatibility in the case a DT does not provide
an avdd-supply, we fall back to calling devm_regulator_get_enable()
so that there is no change in user-facing behavior (e.g. dummy regulator
will still be in sysfs).

Also add an informative error message when we failed to get the voltage
and knowing the voltage is required while we are touching this.
Signed-off-by: David Lechner <dlechner@baylibre.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20240429-regulator-get-enable-get-votlage-v2-4-b1f11ab766c1@baylibre.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/iio/addac/ad74115.c

@@ -199,7 +199,6 @@ struct ad74115_state {
 	struct spi_device		*spi;
 	struct regmap			*regmap;
 	struct iio_trigger		*trig;
-	struct regulator		*avdd;
 
 	/*
 	 * Synchronize consecutive operations when doing a one-shot
@@ -1672,13 +1671,9 @@ static int ad74115_setup(struct iio_dev *indio_dev)
 	if (ret)
 		return ret;
 
-	if (val == AD74115_DIN_THRESHOLD_MODE_AVDD) {
-		ret = regulator_get_voltage(st->avdd);
-		if (ret < 0)
-			return ret;
-
-		st->avdd_mv = ret / 1000;
-	}
+	if (val == AD74115_DIN_THRESHOLD_MODE_AVDD && !st->avdd_mv)
+		return dev_err_probe(dev, -EINVAL,
+				     "AVDD voltage is required for digital input threshold mode AVDD\n");
 
 	st->din_threshold_mode = val;
 
@@ -1788,11 +1783,6 @@ static int ad74115_reset(struct ad74115_state *st)
 	return 0;
 }
 
-static void ad74115_regulator_disable(void *data)
-{
-	regulator_disable(data);
-}
-
 static int ad74115_setup_trigger(struct iio_dev *indio_dev)
 {
 	struct ad74115_state *st = iio_priv(indio_dev);
@@ -1855,20 +1845,20 @@ static int ad74115_probe(struct spi_device *spi)
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->info = &ad74115_info;
 
-	st->avdd = devm_regulator_get(dev, "avdd");
-	if (IS_ERR(st->avdd))
-		return PTR_ERR(st->avdd);
-
-	ret = regulator_enable(st->avdd);
-	if (ret) {
-		dev_err(dev, "Failed to enable avdd regulator\n");
-		return ret;
+	ret = devm_regulator_get_enable_read_voltage(dev, "avdd");
+	if (ret < 0) {
+		/*
+		 * Since this is both a power supply and only optionally a
+		 * reference voltage, make sure to enable it even when the
+		 * voltage is not available.
+		 */
+		ret = devm_regulator_get_enable(dev, "avdd");
+		if (ret)
+			return dev_err_probe(dev, ret, "failed to enable avdd\n");
+	} else {
+		st->avdd_mv = ret / 1000;
 	}
 
-	ret = devm_add_action_or_reset(dev, ad74115_regulator_disable, st->avdd);
-	if (ret)
-		return ret;
-
 	ret = devm_regulator_bulk_get_enable(dev, ARRAY_SIZE(regulator_names),
 					     regulator_names);
 	if (ret)