linux-kernel - [PATCH 3.16 117/178] iio: core: Fix IIO_VAL_FRACTIONAL

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Date:   Sun, 16 Jul 2017 14:56:46 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Nikolaus Schulz" <nikolaus.schulz@...onic-design.de>,
        "Lars-Peter Clausen" <lars@...afoo.de>,
        "Jonathan Cameron" <jic23@...nel.org>
Subject: [PATCH 3.16 117/178] iio: core: Fix IIO_VAL_FRACTIONAL_LOG2 for
 negative values

3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nikolaus Schulz <nikolaus.schulz@...onic-design.de>

commit 7fd6592d1287046f61bfd3cda3c03cd35be490f7 upstream.

Fix formatting of negative values of type IIO_VAL_FRACTIONAL_LOG2 by
switching from do_div(), which can't handle negative numbers, to
div_s64_rem().  Also use shift_right for shifting, which is safe with
negative values.

Signed-off-by: Nikolaus Schulz <nikolaus.schulz@...onic-design.de>
Reviewed-by: Lars-Peter Clausen <lars@...afoo.de>
Signed-off-by: Jonathan Cameron <jic23@...nel.org>
[bwh: Backported to 3.16:
 - Use vals[] instead of tmp{0,1}
 - Keep using sprintf()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/iio/industrialio-core.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -406,10 +406,9 @@ ssize_t iio_format_value(char *buf, unsi
 		vals[0] = (int)div_s64_rem(tmp, 1000000000, &vals[1]);
 		return sprintf(buf, "%d.%09u\n", vals[0], abs(vals[1]));
 	case IIO_VAL_FRACTIONAL_LOG2:
-		tmp = (s64)vals[0] * 1000000000LL >> vals[1];
-		vals[1] = do_div(tmp, 1000000000LL);
-		vals[0] = tmp;
-		return sprintf(buf, "%d.%09u\n", vals[0], vals[1]);
+		tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
+		vals[0] = (int)div_s64_rem(tmp, 1000000000LL, &vals[1]);
+		return sprintf(buf, "%d.%09u\n", vals[0], abs(vals[1]));
 	case IIO_VAL_INT_MULTIPLE:
 	{
 		int i;