[PATCH v4 2/4] iio: adc: ad799x: cache regulator voltage during probe

[Archit Anant]

Reading the regulator voltage via regulator_get_voltage() can be a slow
operation. Since the reference voltage for this ADC is not expected to
change at runtime, it is inefficient to query the regulator API every
time userspace reads the IIO_CHAN_INFO_SCALE attribute.

Determine the active reference voltage (either VREF or VCC) during
probe() and cache it in a single variable in the state structure.
This improves the performance of ad799x_read_raw(), removes the
dependency on the regulator pointers during fast-path reads, and
allows the removal of a redundant negative-value check.

Suggested-by: Jonathan Cameron <jic23@xxxxxxxxxx>
Suggested-by: David Lechner <dlechner@xxxxxxxxxxxx>
Signed-off-by: Archit Anant <architanant5@xxxxxxxxx>
---
 drivers/iio/adc/ad799x.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/adc/ad799x.c b/drivers/iio/adc/ad799x.c
index c1a7fa37706f..28f1901698a6 100644
--- a/drivers/iio/adc/ad799x.c
+++ b/drivers/iio/adc/ad799x.c
@@ -135,6 +135,9 @@ struct ad799x_state {
 	u16				config;
 
 	unsigned int			transfer_size;
+
+	int				vref_uV;
+
 	IIO_DECLARE_BUFFER_WITH_TS(__be16, rx_buf, AD799X_MAX_CHANNELS);
 };
 
@@ -302,14 +305,7 @@ static int ad799x_read_raw(struct iio_dev *indio_dev,
 			GENMASK(chan->scan_type.realbits - 1, 0);
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
-		if (st->vref)
-			ret = regulator_get_voltage(st->vref);
-		else
-			ret = regulator_get_voltage(st->reg);
-
-		if (ret < 0)
-			return ret;
-		*val = ret / 1000;
+		*val = st->vref_uV / 1000;
 		*val2 = chan->scan_type.realbits;
 		return IIO_VAL_FRACTIONAL_LOG2;
 	}
@@ -809,6 +805,10 @@ static int ad799x_probe(struct i2c_client *client)
 	ret = regulator_enable(st->reg);
 	if (ret)
 		return ret;
+	ret = regulator_get_voltage(st->reg);
+	if (ret < 0)
+		goto error_disable_reg;
+	st->vref_uV = ret;
 
 	/* check if an external reference is supplied */
 	if (chip_info->has_vref) {
@@ -827,6 +827,11 @@ static int ad799x_probe(struct i2c_client *client)
 			ret = regulator_enable(st->vref);
 			if (ret)
 				goto error_disable_reg;
+
+			ret = regulator_get_voltage(st->vref);
+			if (ret < 0)
+				goto error_disable_vref;
+			st->vref_uV = ret;
 		}
 	}
 
-- 
2.39.5