iio:core: fix IIO_VAL_FRACTIONAL sign handling

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 159ede6..7ede941 100644 (file)
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -447,9 +447,8 @@ ssize_t iio_format_value(char *buf, unsigned int type, int size, int *vals)
                        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);