[PATCH v6 09/13] iio: afe: rescale: fix precision on fractional log scale

[Liam Beguin]

From: Liam Beguin <lvb@xxxxxxxxxx>

The IIO_VAL_FRACTIONAL_LOG2 scale type doesn't return the expected
scale. Update the case so that the rescaler returns a fractional type
and a more precise scale.

Signed-off-by: Liam Beguin <lvb@xxxxxxxxxx>
---
 drivers/iio/afe/iio-rescale.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 35fa3b4e53e0..47cd4a6d9aca 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -44,12 +44,9 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 		*val2 = rescale->denominator;
 		return IIO_VAL_FRACTIONAL;
 	case IIO_VAL_FRACTIONAL_LOG2:
-		tmp = *val * 1000000000LL;
-		do_div(tmp, rescale->denominator);
-		tmp *= rescale->numerator;
-		do_div(tmp, 1000000000LL);
-		*val = tmp;
-		return scale_type;
+		*val = rescale->numerator * *val;
+		*val2 = rescale->denominator * (1 << *val2);
+		return IIO_VAL_FRACTIONAL;
 	case IIO_VAL_INT_PLUS_NANO:
 		tmp = ((s64)*val * 1000000000LL + *val2) * rescale->numerator;
 		tmp = div_s64(tmp, rescale->denominator);
-- 
2.30.1.489.g328c10930387