The manual for the HSCDTD008A gives us a scaling for the
three axis as +/- 2.4mT per axis.
When I implement this the biggest axis indicates 0.59 Gauss
which is a reasonable measurement for the earths magnetic
which is in the range of 0.25 to 0.65 Gauss on the surface
according to Wikipedia.
Cc: Nick Reitemeyer <nick.reitemeyer@xxxxxx>
Cc: Stephan Gerhold <stephan@xxxxxxxxxxx>
Cc: Michał Mirosław <mirq-linux@xxxxxxxxxxxx>
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
ChangeLog v1->v2:
- Split out the measurement refactoring.
---
drivers/iio/magnetometer/ak8974.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/iio/magnetometer/ak8974.c b/drivers/iio/magnetometer/ak8974.c
index 5361647b9054..effcdd93e650 100644
--- a/drivers/iio/magnetometer/ak8974.c
+++ b/drivers/iio/magnetometer/ak8974.c
@@ -603,6 +603,18 @@ static int ak8974_read_raw(struct iio_dev *indio_dev,
*val = outval;
ret = IIO_VAL_INT;
break;
+ case IIO_CHAN_INFO_SCALE:
+ /*
+ * The datasheet for HSCDTF008A, page 3 specifies the
+ * range of the sensor as +/- 2.4 mT per axis, which corresponds
+ * to +/- 2400 uT = +/- 24 Gauss. So 0x7fff is 24 Gauss and
+ * 0xffff is -24 Gauss. To account for the one missing value if
+ * we multiply by 1/S16_MAX, instead multiply with 2/U16_MAX.
+ */
+ *val = 24 * 2;
+ *val2 = U16_MAX;
+ ret = IIO_VAL_FRACTIONAL;
+ break;
}
out_err_read:
return ret;
@@ -667,7 +679,8 @@ static const struct iio_chan_spec_ext_info ak8974_ext_info[] = {
.type = IIO_MAGN, \
.modified = 1, \
.channel2 = IIO_MOD_##axis, \
- .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
+ .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
+ BIT(IIO_CHAN_INFO_SCALE), \
.ext_info = ak8974_ext_info, \
.address = index, \
.scan_index = index, \
--
2.21.1
