iio: bu27034: Add a read only HARDWAREGAIN

The ROHM BU27034 light sensor has two data channels for measuring
different frequencies of light. The result from these channels is
combined into Lux value while the raw channel values are reported via
intensity channels.

Both of the intensity channels have adjustable gain setting which
impacts the scale of the raw channels. Eg, doubling the gain will double
the values read from the raw channels, which halves the scale value. The
integration time can also be set for the sensor. This does also have an
impact to the scale of the intensity channels because increasing the
integration time will also increase the values reported via the raw
channels.

Impact of integration time to the scale and the fact that the scale value
does not start from '1', can make it hard for a human reader to compute the
gain values based on the scale.

Add read-only HARDWAREGAIN to help debugging.
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://patch.msgid.link/ec349847cc994f3bd632e99b408a31e7c70581d0.1720176341.git.mazziesaccount@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/rohm-bu27034.c

@@ -148,7 +148,8 @@ static const struct iio_itime_sel_mul bu27034_itimes[] = {
 	.type = IIO_INTENSITY,						\
 	.channel = BU27034_CHAN_##_name,				\
 	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |			\
-			      BIT(IIO_CHAN_INFO_SCALE),			\
+			      BIT(IIO_CHAN_INFO_SCALE) |		\
+			      BIT(IIO_CHAN_INFO_HARDWAREGAIN),		\
 	.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),	\
 	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_INT_TIME),		\
 	.info_mask_shared_by_all_available =				\
@@ -989,6 +990,13 @@ static int bu27034_read_raw(struct iio_dev *idev,
 
 		return IIO_VAL_INT_PLUS_MICRO;
 
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		ret = bu27034_get_gain(data, chan->channel, val);
+		if (ret)
+			return ret;
+
+		return IIO_VAL_INT;
+
 	case IIO_CHAN_INFO_SCALE:
 		return bu27034_get_scale(data, chan->channel, val, val2);
 
@@ -1033,12 +1041,17 @@ static int bu27034_write_raw_get_fmt(struct iio_dev *indio_dev,
 				     struct iio_chan_spec const *chan,
 				     long mask)
 {
+	struct bu27034_data *data = iio_priv(indio_dev);
 
 	switch (mask) {
 	case IIO_CHAN_INFO_SCALE:
 		return IIO_VAL_INT_PLUS_NANO;
 	case IIO_CHAN_INFO_INT_TIME:
 		return IIO_VAL_INT_PLUS_MICRO;
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		dev_dbg(data->dev,
+			"HARDWAREGAIN is read-only, use scale to set\n");
+		return -EINVAL;
 	default:
 		return -EINVAL;
 	}