Commit f5fc003d authored by Liam Beguin's avatar Liam Beguin Committed by Jonathan Cameron
Browse files

iio: afe: rescale: fix accuracy for small fractional scales 



The approximation caused by integer divisions can be costly on smaller
scale values since the decimal part is significant compared to the
integer part. Switch to an IIO_VAL_INT_PLUS_NANO scale type in such
cases to maintain accuracy.

Signed-off-by: default avatarLiam Beguin <liambeguin@gmail.com>
Reviewed-by: default avatarPeter Rosin <peda@axentia.se>
Reviewed-by: default avatarAndy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220213025739.2561834-5-liambeguin@gmail.com


Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
parent a29c3283

drivers/iio/afe/iio-rescale.c

+17 −3
Original line number Diff line number Diff line
@@ -24,7 +24,7 @@ int rescale_process_scale(struct rescale *rescale, int scale_type, 
			  int *val, int *val2)

{

	s64 tmp;

	s32 rem;

	s32 rem, rem2;

	u32 mult;

	u32 neg;
@@ -43,9 +43,23 @@ int rescale_process_scale(struct rescale *rescale, int scale_type, 
		tmp = (s64)*val * 1000000000LL;

		tmp = div_s64(tmp, rescale->denominator);

		tmp *= rescale->numerator;

		tmp = div_s64(tmp, 1000000000LL);



		tmp = div_s64_rem(tmp, 1000000000LL, &rem);

		*val = tmp;



		if (!rem)

			return scale_type;



		tmp = 1 << *val2;



		rem2 = *val % (int)tmp;

		*val = *val / (int)tmp;



		*val2 = rem / (int)tmp;

		if (rem2)

			*val2 += div_s64((s64)rem2 * 1000000000LL, tmp);



		return IIO_VAL_INT_PLUS_NANO;

	case IIO_VAL_INT_PLUS_NANO:

	case IIO_VAL_INT_PLUS_MICRO:

		mult = scale_type == IIO_VAL_INT_PLUS_NANO ? 1000000000L : 1000000L;