staging:iio:ad2s90: Add IIO_CHAN_INFO_SCALE to channel spec and read_raw

This patch adds the IIO_CHAN_INFO_SCALE mask to ad2s90_chan and
implements the relative read behavior at ad2s90_read_raw.
Signed-off-by: Victor Colombo <victorcolombo@gmail.com>
Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/resolver/ad2s90.c

@@ -34,6 +34,13 @@ static int ad2s90_read_raw(struct iio_dev *indio_dev,
 	int ret;
 	struct ad2s90_state *st = iio_priv(indio_dev);
 
+	switch (m) {
+	case IIO_CHAN_INFO_SCALE:
+		/* 2 * Pi / 2^12 */
+		*val = 6283; /* mV */
+		*val2 = 12;
+		return IIO_VAL_FRACTIONAL_LOG2;
+	case IIO_CHAN_INFO_RAW:
 		mutex_lock(&st->lock);
 		ret = spi_read(st->sdev, st->rx, 2);
 		if (ret < 0) {
@@ -45,6 +52,11 @@ static int ad2s90_read_raw(struct iio_dev *indio_dev,
 		mutex_unlock(&st->lock);
 
 		return IIO_VAL_INT;
+	default:
+		break;
+	}
+
+	return -EINVAL;
 }
 
 static const struct iio_info ad2s90_info = {
@@ -55,7 +67,7 @@ static const struct iio_chan_spec ad2s90_chan = {
 	.type = IIO_ANGL,
 	.indexed = 1,
 	.channel = 0,
-	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
 };
 
 static int ad2s90_probe(struct spi_device *spi)