iio: adc: ad7949: add vref selection support

Add support for selecting the voltage reference from the devicetree.

This change is required to get valid readings with all three
vref hardware configurations supported by the ADC.

For instance if the ADC isn't provided with an external reference,
the sample request must specify an internal voltage reference to get a
valid reading.
Signed-off-by: Liam Beguin <lvb@xiphos.com>
Link: https://lore.kernel.org/r/20210815213309.2847711-4-liambeguin@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7949.c

@@ -35,7 +35,11 @@
 
 /* REF: reference/buffer selection */
 #define AD7949_CFG_MASK_REF		GENMASK(5, 3)
-#define AD7949_CFG_VAL_REF_EXT_BUF		7
+#define AD7949_CFG_VAL_REF_EXT_TEMP_BUF		3
+#define AD7949_CFG_VAL_REF_EXT_TEMP		2
+#define AD7949_CFG_VAL_REF_INT_4096		1
+#define AD7949_CFG_VAL_REF_INT_2500		0
+#define AD7949_CFG_VAL_REF_EXTERNAL		BIT(1)
 
 /* SEQ: channel sequencer. Allows for scanning channels */
 #define AD7949_CFG_MASK_SEQ		GENMASK(2, 1)
@@ -66,6 +70,7 @@ static const struct ad7949_adc_spec ad7949_adc_spec[] = {
  * @vref: regulator generating Vref
  * @indio_dev: reference to iio structure
  * @spi: reference to spi structure
+ * @refsel: reference selection
  * @resolution: resolution of the chip
  * @cfg: copy of the configuration register
  * @current_channel: current channel in use
@@ -77,6 +82,7 @@ struct ad7949_adc_chip {
 	struct regulator *vref;
 	struct iio_dev *indio_dev;
 	struct spi_device *spi;
+	u32 refsel;
 	u8 resolution;
 	u16 cfg;
 	unsigned int current_channel;
@@ -221,12 +227,26 @@ static int ad7949_spi_read_raw(struct iio_dev *indio_dev,
 		return IIO_VAL_INT;
 
 	case IIO_CHAN_INFO_SCALE:
+		switch (ad7949_adc->refsel) {
+		case AD7949_CFG_VAL_REF_INT_2500:
+			*val = 2500;
+			break;
+		case AD7949_CFG_VAL_REF_INT_4096:
+			*val = 4096;
+			break;
+		case AD7949_CFG_VAL_REF_EXT_TEMP:
+		case AD7949_CFG_VAL_REF_EXT_TEMP_BUF:
 			ret = regulator_get_voltage(ad7949_adc->vref);
 			if (ret < 0)
 				return ret;
 
-		*val = ret / 5000;
-		return IIO_VAL_INT;
+			/* convert value back to mV */
+			*val = ret / 1000;
+			break;
+		}
+
+		*val2 = (1 << ad7949_adc->resolution) - 1;
+		return IIO_VAL_FRACTIONAL;
 	}
 
 	return -EINVAL;
@@ -265,7 +285,7 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
 		FIELD_PREP(AD7949_CFG_MASK_INCC, AD7949_CFG_VAL_INCC_UNIPOLAR_GND) |
 		FIELD_PREP(AD7949_CFG_MASK_INX, ad7949_adc->current_channel) |
 		FIELD_PREP(AD7949_CFG_MASK_BW_FULL, 1) |
-		FIELD_PREP(AD7949_CFG_MASK_REF, AD7949_CFG_VAL_REF_EXT_BUF) |
+		FIELD_PREP(AD7949_CFG_MASK_REF, ad7949_adc->refsel) |
 		FIELD_PREP(AD7949_CFG_MASK_SEQ, 0x0) |
 		FIELD_PREP(AD7949_CFG_MASK_RBN, 1);
 
@@ -281,6 +301,11 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
 	return ret;
 }
 
+static void ad7949_disable_reg(void *reg)
+{
+	regulator_disable(reg);
+}
+
 static int ad7949_spi_probe(struct spi_device *spi)
 {
 	u32 spi_ctrl_mask = spi->controller->bits_per_word_mask;
@@ -288,6 +313,7 @@ static int ad7949_spi_probe(struct spi_device *spi)
 	const struct ad7949_adc_spec *spec;
 	struct ad7949_adc_chip *ad7949_adc;
 	struct iio_dev *indio_dev;
+	u32 tmp;
 	int ret;
 
 	indio_dev = devm_iio_device_alloc(dev, sizeof(*ad7949_adc));
@@ -322,18 +348,54 @@ static int ad7949_spi_probe(struct spi_device *spi)
 		return -EINVAL;
 	}
 
-	ad7949_adc->vref = devm_regulator_get(dev, "vref");
+	/* Setup internal voltage reference */
+	tmp = 4096000;
+	device_property_read_u32(dev, "adi,internal-ref-microvolt", &tmp);
+
+	switch (tmp) {
+	case 2500000:
+		ad7949_adc->refsel = AD7949_CFG_VAL_REF_INT_2500;
+		break;
+	case 4096000:
+		ad7949_adc->refsel = AD7949_CFG_VAL_REF_INT_4096;
+		break;
+	default:
+		dev_err(dev, "unsupported internal voltage reference\n");
+		return -EINVAL;
+	}
+
+	/* Setup external voltage reference, buffered? */
+	ad7949_adc->vref = devm_regulator_get_optional(dev, "vrefin");
 	if (IS_ERR(ad7949_adc->vref)) {
-		dev_err(dev, "fail to request regulator\n");
-		return PTR_ERR(ad7949_adc->vref);
+		ret = PTR_ERR(ad7949_adc->vref);
+		if (ret != -ENODEV)
+			return ret;
+		/* unbuffered? */
+		ad7949_adc->vref = devm_regulator_get_optional(dev, "vref");
+		if (IS_ERR(ad7949_adc->vref)) {
+			ret = PTR_ERR(ad7949_adc->vref);
+			if (ret != -ENODEV)
+				return ret;
+		} else {
+			ad7949_adc->refsel = AD7949_CFG_VAL_REF_EXT_TEMP;
+		}
+	} else {
+		ad7949_adc->refsel = AD7949_CFG_VAL_REF_EXT_TEMP_BUF;
 	}
 
+	if (ad7949_adc->refsel & AD7949_CFG_VAL_REF_EXTERNAL) {
 		ret = regulator_enable(ad7949_adc->vref);
 		if (ret < 0) {
 			dev_err(dev, "fail to enable regulator\n");
 			return ret;
 		}
 
+		ret = devm_add_action_or_reset(dev, ad7949_disable_reg,
+					       ad7949_adc->vref);
+		if (ret)
+			return ret;
+	}
+
 	mutex_init(&ad7949_adc->lock);
 
 	ret = ad7949_spi_init(ad7949_adc);
@@ -352,7 +414,6 @@ static int ad7949_spi_probe(struct spi_device *spi)
 
 err:
 	mutex_destroy(&ad7949_adc->lock);
-	regulator_disable(ad7949_adc->vref);
 
 	return ret;
 }
@@ -364,7 +425,6 @@ static int ad7949_spi_remove(struct spi_device *spi)
 
 	iio_device_unregister(indio_dev);
 	mutex_destroy(&ad7949_adc->lock);
-	regulator_disable(ad7949_adc->vref);
 
 	return 0;
 }