iio: adc: ad7091r5: Add scale and external VREF support

The scale can now be obtained with the "in_voltage_scale" file.
By default, the scale returned corresponds to the internal VREF of 2.5V.

It is possible to use an external VREF (through the REFIN/REFOUT pin of
the chip), by passing a regulator to the driver. The scale will then be
calculated according to the voltage reported by the regulator.

Signed-off-by: Paul Cercueil <[e-mail]>
Co-developed-by: Beniamin Bia <[e-mail]>
Signed-off-by: Beniamin Bia <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/ad7091r-base.c

···
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
 
 #include "ad7091r-base.h"
 
···
 struct ad7091r_state {
 	struct device *dev;
 	struct regmap *map;
+	struct regulator *vref;
 	const struct ad7091r_chip_info *chip_info;
 	enum ad7091r_mode mode;
 	struct mutex lock; /*lock to prevent concurent reads */
···
 		ret = IIO_VAL_INT;
 		break;
 
+	case IIO_CHAN_INFO_SCALE:
+		if (st->vref) {
+			ret = regulator_get_voltage(st->vref);
+			if (ret < 0)
+				goto unlock;
+
+			*val = ret / 1000;
+		} else {
+			*val = st->chip_info->vref_mV;
+		}
+
+		*val2 = chan->scan_type.realbits;
+		ret = IIO_VAL_FRACTIONAL_LOG2;
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
···
 	return IRQ_HANDLED;
 }
 
+static void ad7091r_remove(void *data)
+{
+	struct ad7091r_state *st = data;
+
+	regulator_disable(st->vref);
+}
+
 int ad7091r_probe(struct device *dev, const char *name,
 		const struct ad7091r_chip_info *chip_info,
 		struct regmap *map, int irq)
···
 		ret = devm_request_threaded_irq(dev, irq, NULL,
 				ad7091r_event_handler,
 				IRQF_TRIGGER_FALLING | IRQF_ONESHOT, name, st);
+		if (ret)
+			return ret;
+	}
+
+	st->vref = devm_regulator_get_optional(dev, "vref");
+	if (IS_ERR(st->vref)) {
+		if (PTR_ERR(st->vref) == -EPROBE_DEFER)
+			return -EPROBE_DEFER;
+		st->vref = NULL;
+	} else {
+		ret = regulator_enable(st->vref);
+		if (ret)
+			return ret;
+		ret = devm_add_action_or_reset(dev, ad7091r_remove, st);
 		if (ret)
 			return ret;
 	}

drivers/iio/adc/ad7091r-base.h

···
 struct ad7091r_chip_info {
 	unsigned int num_channels;
 	const struct iio_chan_spec *channels;
+	unsigned int vref_mV;
 };
 
 extern const struct regmap_config ad7091r_regmap_config;

drivers/iio/adc/ad7091r5.c

···
 #define AD7091R_CHANNEL(idx, bits, ev, num_ev) { \
 	.type = IIO_VOLTAGE, \
 	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
 	.indexed = 1, \
 	.channel = idx, \
 	.event_spec = ev, \
 	.num_event_specs = num_ev, \
+	.scan_type.storagebits = 16, \
+	.scan_type.realbits = bits, \
 }
 static const struct iio_chan_spec ad7091r5_channels_irq[] = {
 	AD7091R_CHANNEL(0, 12, ad7091r5_events, ARRAY_SIZE(ad7091r5_events)),
···
 static const struct ad7091r_chip_info ad7091r5_chip_info_irq = {
 	.channels = ad7091r5_channels_irq,
 	.num_channels = ARRAY_SIZE(ad7091r5_channels_irq),
+	.vref_mV = 2500,
 };
 
 static const struct ad7091r_chip_info ad7091r5_chip_info_noirq = {
 	.channels = ad7091r5_channels_noirq,
 	.num_channels = ARRAY_SIZE(ad7091r5_channels_noirq),
+	.vref_mV = 2500,
 };
 
 static int ad7091r5_i2c_probe(struct i2c_client *i2c,