[PATCH v2 3/4] iio: adc: ad7949: add support for internal vref

[Liam Beguin]

From: Liam Beguin <lvb@xxxxxxxxxx>

Add support for selecting a custom reference voltage from the
devicetree. If an external source is used, a vref regulator should be
defined in the devicetree.

Signed-off-by: Liam Beguin <lvb@xxxxxxxxxx>
---
 drivers/iio/adc/ad7949.c | 94 ++++++++++++++++++++++++++++++++++------
 1 file changed, 80 insertions(+), 14 deletions(-)

diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
index 770112ac820f..a20fd81a0830 100644
--- a/drivers/iio/adc/ad7949.c
+++ b/drivers/iio/adc/ad7949.c
@@ -31,6 +31,7 @@
 #define AD7949_CFG_VAL_BW_FULL			1
 #define AD7949_CFG_VAL_BW_QUARTER		0
 #define AD7949_CFG_BIT_REF		GENMASK(5, 3)
+#define AD7949_CFG_VAL_REF_EXTERNAL		BIT(1)
 #define AD7949_CFG_BIT_SEQ		GENMASK(2, 1)
 #define AD7949_CFG_BIT_RBN		BIT(0)
 
@@ -40,6 +41,33 @@ enum {
 	ID_AD7689,
 };
 
+/**
+ * enum ad7949_ref - Reference selection
+ *
+ * AD7949_REF_INT_2500:     Internal reference and temperature sensor enabled.
+ *                          Vref=2.5V, buffered output
+ * AD7949_REF_INT_4096:     Internal reference and temperature sensor enabled.
+ *                          Vref=4.096V, buffered output
+ * AD7949_REF_EXT_TEMP:     Use external reference, temperature sensor enabled.
+ *                          Internal buffer disabled
+ * AD7949_REF_EXT_TEMP_BUF: Use external reference, internal buffer and
+ *                          temperature sensor enabled.
+ * AD7949_REF_RSRV_4:       Do not use
+ * AD7949_REF_RSRV_5:       Do not use
+ * AD7949_REF_EXT:          Use external reference, internal buffer and
+ *                          temperature sensor disabled.
+ * AD7949_REF_EXT_BUF:      Use external reference, internal buffer enabled.
+ *                          Internal reference and temperature sensor disabled.
+ */
+enum ad7949_ref {
+	AD7949_REF_INT_2500 = 0,
+	AD7949_REF_INT_4096,
+	AD7949_REF_EXT_TEMP,
+	AD7949_REF_EXT_TEMP_BUF,
+	AD7949_REF_EXT = 6,
+	AD7949_REF_EXT_BUF,
+};
+
 struct ad7949_adc_spec {
 	u8 num_channels;
 	u8 resolution;
@@ -55,6 +83,7 @@ static const struct ad7949_adc_spec ad7949_adc_spec[] = {
  * struct ad7949_adc_chip - AD ADC chip
  * @lock: protects write sequences
  * @vref: regulator generating Vref
+ * @refsel: reference selection
  * @indio_dev: reference to iio structure
  * @spi: reference to spi structure
  * @resolution: resolution of the chip
@@ -66,6 +95,7 @@ static const struct ad7949_adc_spec ad7949_adc_spec[] = {
 struct ad7949_adc_chip {
 	struct mutex lock;
 	struct regulator *vref;
+	enum ad7949_ref refsel;
 	struct iio_dev *indio_dev;
 	struct spi_device *spi;
 	u8 resolution;
@@ -243,12 +273,28 @@ static int ad7949_spi_read_raw(struct iio_dev *indio_dev,
 		return IIO_VAL_INT;
 
 	case IIO_CHAN_INFO_SCALE:
-		ret = regulator_get_voltage(ad7949_adc->vref);
-		if (ret < 0)
-			return ret;
+		switch (ad7949_adc->refsel) {
+		case AD7949_REF_INT_2500:
+			*val = 2500;
+			break;
+		case AD7949_REF_INT_4096:
+			*val = 4096;
+			break;
+		case AD7949_REF_EXT_TEMP:
+		case AD7949_REF_EXT_TEMP_BUF:
+		case AD7949_REF_EXT:
+		case AD7949_REF_EXT_BUF:
+			ret = regulator_get_voltage(ad7949_adc->vref);
+			if (ret < 0)
+				return ret;
+
+			/* convert value back to mV */
+			*val = ret / 1000;
+			break;
+		}
 
-		*val = ret / 5000;
-		return IIO_VAL_INT;
+		*val2 = (1 << ad7949_adc->resolution) - 1;
+		return IIO_VAL_FRACTIONAL;
 	}
 
 	return -EINVAL;
@@ -287,7 +333,7 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
 		FIELD_PREP(AD7949_CFG_BIT_INCC, AD7949_CFG_VAL_INCC_UNIPOLAR_GND) |
 		FIELD_PREP(AD7949_CFG_BIT_INX, ad7949_adc->current_channel) |
 		FIELD_PREP(AD7949_CFG_BIT_BW, AD7949_CFG_VAL_BW_FULL) |
-		FIELD_PREP(AD7949_CFG_BIT_REF, AD7949_REF_EXT_BUF) |
+		FIELD_PREP(AD7949_CFG_BIT_REF, ad7949_adc->refsel) |
 		FIELD_PREP(AD7949_CFG_BIT_SEQ, 0x0) |
 		FIELD_PREP(AD7949_CFG_BIT_RBN, 1);
 
@@ -306,6 +352,7 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
 static int ad7949_spi_probe(struct spi_device *spi)
 {
 	struct device *dev = &spi->dev;
+	struct device_node *np = dev->of_node;
 	const struct ad7949_adc_spec *spec;
 	struct ad7949_adc_chip *ad7949_adc;
 	struct iio_dev *indio_dev;
@@ -332,16 +379,35 @@ static int ad7949_spi_probe(struct spi_device *spi)
 	ad7949_adc->resolution = spec->resolution;
 	ad7949_set_bits_per_word(ad7949_adc);
 
-	ad7949_adc->vref = devm_regulator_get(dev, "vref");
-	if (IS_ERR(ad7949_adc->vref)) {
-		dev_err(dev, "fail to request regulator\n");
-		return PTR_ERR(ad7949_adc->vref);
+	/* Set default devicetree parameters */
+	ad7949_adc->refsel = AD7949_REF_EXT_BUF;
+	of_property_read_u32(np, "adi,reference-select", &ad7949_adc->refsel);
+	switch (ad7949_adc->refsel) {
+	case AD7949_REF_INT_2500:
+	case AD7949_REF_INT_4096:
+	case AD7949_REF_EXT_TEMP:
+	case AD7949_REF_EXT_TEMP_BUF:
+	case AD7949_REF_EXT:
+	case AD7949_REF_EXT_BUF:
+		break;
+	default:
+		dev_err(dev, "invalid adi,reference-select value (%d)\n",
+			ad7949_adc->refsel);
+		return -EINVAL;
 	}
 
-	ret = regulator_enable(ad7949_adc->vref);
-	if (ret < 0) {
-		dev_err(dev, "fail to enable regulator\n");
-		return ret;
+	if (ad7949_adc->refsel & AD7949_CFG_VAL_REF_EXTERNAL) {
+		ad7949_adc->vref = devm_regulator_get(dev, "vref");
+		if (IS_ERR(ad7949_adc->vref)) {
+			dev_err(dev, "fail to request regulator\n");
+			return PTR_ERR(ad7949_adc->vref);
+		}
+
+		ret = regulator_enable(ad7949_adc->vref);
+		if (ret < 0) {
+			dev_err(dev, "fail to enable regulator\n");
+			return ret;
+		}
 	}
 
 	mutex_init(&ad7949_adc->lock);
-- 
2.30.1.489.g328c10930387