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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@parrot.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@parrot.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.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);
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