linux-kernel - [PATCH 3.16 252/346] iio:core: fix IIO_VAL

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Message-ID: <lsq.1479082460.317647747@decadent.org.uk>
Date:   Mon, 14 Nov 2016 00:14:20 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Gregor Boirie" <gregor.boirie@...rot.com>,
        "Jonathan Cameron" <jic23@...nel.org>,
        "Lars-Peter Clausen" <lars@...afoo.de>
Subject: [PATCH 3.16 252/346] iio:core: fix IIO_VAL_FRACTIONAL sign handling

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

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

From: Gregor Boirie <gregor.boirie@...rot.com>

commit 171c0091837c81ed5c949fec6966bb5afff2d1cf upstream.

7985e7c100 ("iio: Introduce a new fractional value type") introduced a
new IIO_VAL_FRACTIONAL value type meant to represent rational type numbers
expressed by a numerator and denominator combination.

Formating of IIO_VAL_FRACTIONAL values relies upon do_div() usage. This
fails handling negative values properly since parameters are reevaluated
as unsigned values.
Fix this by using div_s64_rem() instead. Computed integer part will carry
properly signed value. Formatted fractional part will always be positive.

Fixes: 7985e7c100 ("iio: Introduce a new fractional value type")
Signed-off-by: Gregor Boirie <gregor.boirie@...rot.com>
Reviewed-by: Lars-Peter Clausen <lars@...afoo.de>
Signed-off-by: Jonathan Cameron <jic23@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/iio/industrialio-core.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -404,9 +404,8 @@ ssize_t iio_format_value(char *buf, unsi
 			return sprintf(buf, "%d.%09u\n", vals[0], vals[1]);
 	case IIO_VAL_FRACTIONAL:
 		tmp = div_s64((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]);
+		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);