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From: Liam Beguin <liambeguin@gmail.com>
To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org,
	lars@metafoo.de, pmeerw@pmeerw.net
Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
	devicetree@vger.kernel.org, robh+dt@kernel.org
Subject: [PATCH v7 08/13] iio: afe: rescale: fix precision on fractional log scale
Date: Sun,  1 Aug 2021 15:39:55 -0400	[thread overview]
Message-ID: <20210801194000.3646303-9-liambeguin@gmail.com> (raw)
In-Reply-To: <20210801194000.3646303-1-liambeguin@gmail.com>

From: Liam Beguin <lvb@xiphos.com>

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@xiphos.com>
---
 drivers/iio/afe/iio-rescale.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index abd7ad73d1ce..e37a9766080c 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -47,12 +47,17 @@ 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);
+		if (check_mul_overflow(*val, rescale->numerator, (s32 *)&tmp) ||
+		    check_mul_overflow(rescale->denominator, (1 << *val2), (s32 *)&tmp2)) {
+			tmp = (s64)*val * rescale->numerator;
+			tmp2 = (s64)rescale->denominator * (1 << *val2);
+			factor = gcd(abs(tmp), abs(tmp2));
+			tmp = div_s64(tmp, factor);
+			tmp2 = div_s64(tmp2, factor);
+		}
 		*val = tmp;
-		return scale_type;
+		*val2 = tmp2;
+		return IIO_VAL_FRACTIONAL;
 	case IIO_VAL_INT_PLUS_NANO:
 	case IIO_VAL_INT_PLUS_MICRO:
 		if (scale_type == IIO_VAL_INT_PLUS_NANO)
-- 
2.30.1.489.g328c10930387


  parent reply	other threads:[~2021-08-01 19:40 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-01 19:39 [PATCH v7 00/13] iio: afe: add temperature rescaling support Liam Beguin
2021-08-01 19:39 ` [PATCH v7 01/13] iio: inkern: apply consumer scale on IIO_VAL_INT cases Liam Beguin
2021-08-01 19:39 ` [PATCH v7 02/13] iio: inkern: apply consumer scale when no channel scale is available Liam Beguin
2021-08-01 19:39 ` [PATCH v7 03/13] iio: inkern: make a best effort on offset calculation Liam Beguin
2021-08-01 19:39 ` [PATCH v7 04/13] iio: afe: rescale: expose scale processing function Liam Beguin
2021-08-01 19:39 ` [PATCH v7 05/13] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support Liam Beguin
2021-08-01 19:39 ` [PATCH v7 06/13] iio: afe: rescale: add offset support Liam Beguin
2021-08-01 19:39 ` [PATCH v7 07/13] iio: afe: rescale: reduce risk of integer overflow Liam Beguin
2021-08-01 19:39 ` Liam Beguin [this message]
2021-08-02  9:17   ` [PATCH v7 08/13] iio: afe: rescale: fix precision on fractional log scale Peter Rosin
2021-08-15 22:14     ` Liam Beguin
2021-08-01 19:39 ` [PATCH v7 09/13] iio: test: add basic tests for the iio-rescale driver Liam Beguin
2021-08-01 19:39 ` [PATCH v7 10/13] iio: afe: rescale: add RTD temperature sensor support Liam Beguin
2021-08-01 19:39 ` [PATCH v7 11/13] iio: afe: rescale: add temperature transducers Liam Beguin
2021-08-01 19:39 ` [PATCH v7 12/13] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Liam Beguin
2021-08-01 19:40 ` [PATCH v7 13/13] dt-bindings: iio: afe: add bindings for temperature transducers Liam Beguin

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