[PATCH] iio: adc: ad799x: Implement selecting external reference voltage input on AD7991, AD7995 and AD7999.

[Florian Boor <florian.boor@kernelconcepts.de>]

Make use of the AD7991_REF_SEL bit and support using the external
reference voltage by setting the 'vref-external' property in devicetree.

Signed-off-by: Florian Boor <florian.boor@kernelconcepts.de>
---
 drivers/iio/adc/ad799x.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/adc/ad799x.c b/drivers/iio/adc/ad799x.c
index 18bf8386d50a..3ae7ec72caa3 100644
--- a/drivers/iio/adc/ad799x.c
+++ b/drivers/iio/adc/ad799x.c
@@ -770,6 +770,7 @@ static int ad799x_probe(struct i2c_client *client,
 				   const struct i2c_device_id *id)
 {
 	int ret;
+	int extra_config = 0;
 	struct ad799x_state *st;
 	struct iio_dev *indio_dev;
 	const struct ad799x_chip_info *chip_info =
@@ -806,6 +807,17 @@ static int ad799x_probe(struct i2c_client *client,
 	if (ret)
 		goto error_disable_reg;
 
+
+	/* allow to use external reference voltage */
+	if ((st->id == ad7991) || (st->id == ad7995) || (st->id == ad7999)) {
+		unsigned int vref_external = 0;
+	        of_property_read_u32(client->dev.of_node, "vref-external",
+			&vref_external);
+
+		if (vref_external)
+			extra_config |= AD7991_REF_SEL;
+	}
+
 	st->client = client;
 
 	indio_dev->name = id->name;
@@ -815,7 +827,7 @@ static int ad799x_probe(struct i2c_client *client,
 	indio_dev->channels = st->chip_config->channel;
 	indio_dev->num_channels = chip_info->num_channels;
 
-	ret = ad799x_update_config(st, st->chip_config->default_config);
+	ret = ad799x_update_config(st, st->chip_config->default_config | extra_config);
 	if (ret)
 		goto error_disable_vref;
 
-- 
2.20.1