iio: adc: ad7298: convert probe to device-managed functions

This change converts the probe of this driver to use device-managed
register functions, and a devm_add_action_or_reset() for the regulator
disable.

With this, the exit & error paths can be removed.
Another side-effect is that this should avoid some static-analyzer's check
with respect to a potential null dereference of the regulator. The null
dereference isn't likely to happen (under normal operation), so there isn't
a requirement to have this fixed/backported in other releases.

As a note: this is removing spi_set_drvdata() since there is no other
spi_get_drvdata() (or dev_get_drvdata()) call that need it.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20201127094038.91714-1-alexandru.ardelean@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7298.c

@@ -279,6 +279,13 @@ static const struct iio_info ad7298_info = {
 	.update_scan_mode = ad7298_update_scan_mode,
 };
 
+static void ad7298_reg_disable(void *data)
+{
+	struct regulator *reg = data;
+
+	regulator_disable(reg);
+}
+
 static int ad7298_probe(struct spi_device *spi)
 {
 	struct ad7298_state *st;
@@ -306,9 +313,12 @@ static int ad7298_probe(struct spi_device *spi)
 		ret = regulator_enable(st->reg);
 		if (ret)
 			return ret;
-	}
 
-	spi_set_drvdata(spi, indio_dev);
+		ret = devm_add_action_or_reset(&spi->dev, ad7298_reg_disable,
+					       st->reg);
+		if (ret)
+			return ret;
+	}
 
 	st->spi = spi;
 
@@ -334,37 +344,12 @@ static int ad7298_probe(struct spi_device *spi)
 	spi_message_add_tail(&st->scan_single_xfer[1], &st->scan_single_msg);
 	spi_message_add_tail(&st->scan_single_xfer[2], &st->scan_single_msg);
 
-	ret = iio_triggered_buffer_setup(indio_dev, NULL,
+	ret = devm_iio_triggered_buffer_setup(&spi->dev, indio_dev, NULL,
 			&ad7298_trigger_handler, NULL);
 	if (ret)
-		goto error_disable_reg;
-
-	ret = iio_device_register(indio_dev);
-	if (ret)
-		goto error_cleanup_ring;
-
-	return 0;
-
-error_cleanup_ring:
-	iio_triggered_buffer_cleanup(indio_dev);
-error_disable_reg:
-	if (st->ext_ref)
-		regulator_disable(st->reg);
-
-	return ret;
-}
-
-static int ad7298_remove(struct spi_device *spi)
-{
-	struct iio_dev *indio_dev = spi_get_drvdata(spi);
-	struct ad7298_state *st = iio_priv(indio_dev);
-
-	iio_device_unregister(indio_dev);
-	iio_triggered_buffer_cleanup(indio_dev);
-	if (st->ext_ref)
-		regulator_disable(st->reg);
+		return ret;
 
-	return 0;
+	return devm_iio_device_register(&spi->dev, indio_dev);
 }
 
 static const struct spi_device_id ad7298_id[] = {
@@ -378,7 +363,6 @@ static struct spi_driver ad7298_driver = {
 		.name	= "ad7298",
 	},
 	.probe		= ad7298_probe,
-	.remove		= ad7298_remove,
 	.id_table	= ad7298_id,
 };
 module_spi_driver(ad7298_driver);