iio: adc: ti_am335x_adc: Add the scale information

Without the scale, the values returned to the user are just a picture of
the input voltage against the full scale range of the ADC. We need to
provide the actual conversion factor to get milli-Volts values.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211015081506.933180-45-miquel.raynal@bootlin.com

drivers/iio/adc/ti_am335x_adc.c

@@ -417,6 +417,7 @@ static int tiadc_channel_init(struct device *dev, struct iio_dev *indio_dev,
 		chan->indexed = 1;
 		chan->channel = adc_dev->channel_line[i];
 		chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
+		chan->info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE);
 		chan->datasheet_name = chan_name_ain[chan->channel];
 		chan->scan_index = i;
 		chan->scan_type.sign = 'u';
@@ -441,6 +442,23 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
 	unsigned long timeout;
 	int ret;
 
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		break;
+	case IIO_CHAN_INFO_SCALE:
+		switch (chan->type) {
+		case IIO_VOLTAGE:
+			*val = 1800;
+			*val2 = chan->scan_type.realbits;
+			return IIO_VAL_FRACTIONAL_LOG2;
+		default:
+			return -EINVAL;
+		}
+		break;
+	default:
+		return -EINVAL;
+	}
+
 	if (iio_buffer_enabled(indio_dev))
 		return -EBUSY;