Hi Jonathan,
I encountered this when I was developing a new driver.
If you look at the function where this is used, all other IIO_VAL_MICRO and NANO
have this fix added at some point.
Thanks,
Anand
> -----Original Message-----
> From: Jonathan Cameron <jic23@xxxxxxxxxx>
> Sent: Saturday, August 29, 2020 4:19 PM
> To: Anand Ashok Dumbre <ANANDASH@xxxxxxxxxx>
> Cc: knaack.h@xxxxxx; lars@xxxxxxxxxx; pmeerw@xxxxxxxxxx; Michal
> Simek <michals@xxxxxxxxxx>; git <git@xxxxxxxxxx>; linux-
> iio@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Anand Ashok Dumbre <ANANDASH@xxxxxxxxxx>
> Subject: Re: [PATCH v2] iio: core: Fix IIO_VAL_FRACTIONAL calculation for
> negative values
>
> On Wed, 26 Aug 2020 11:14:36 -0700
> Anand Ashok Dumbre <anand.ashok.dumbre@xxxxxxxxxx> wrote:
>
> > Fixes IIO_VAL_FRACTIONAL for case when the result is negative and
> > exponent is 0.
> >
> > example: if the result is -0.75, tmp0 will be 0 and tmp1 = 75 This
> > causes the output to lose sign because of %d in snprintf which works
> > for tmp0 <= -1.
> >
> > Signed-off-by: Anand Ashok Dumbre <anand.ashok.dumbre@xxxxxxxxxx>
>
> Looks good. Just one last thing.
>
> Is this actually hit in an existing driver? I'm just wondering how far back we
> need to push it in stable etc.
>
> Thanks,
>
> Jonathan
>
> > ---
> > changes since v1:
> > Changed -%d to -0 to make the fix clearer.
> > Removed the email footer.
> > Updated the commit description with an example
> > --
> > drivers/iio/industrialio-core.c | 8 ++++++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iio/industrialio-core.c
> > b/drivers/iio/industrialio-core.c index cdcd16f1..a239fa2 100644
> > --- a/drivers/iio/industrialio-core.c
> > +++ b/drivers/iio/industrialio-core.c
> > @@ -592,6 +592,7 @@ static ssize_t __iio_format_value(char *buf,
> > size_t len, unsigned int type, {
> > unsigned long long tmp;
> > int tmp0, tmp1;
> > + s64 tmp2;
> > bool scale_db = false;
> >
> > switch (type) {
> > @@ -614,10 +615,13 @@ static ssize_t __iio_format_value(char *buf,
> size_t len, unsigned int type,
> > else
> > return scnprintf(buf, len, "%d.%09u", vals[0], vals[1]);
> > case IIO_VAL_FRACTIONAL:
> > - tmp = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
> > + tmp2 = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
> > tmp1 = vals[1];
> > tmp0 = (int)div_s64_rem(tmp, 1000000000, &tmp1);
> > - return scnprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
> > + if ((tmp2 < 0) && (tmp0 == 0))
> > + return snprintf(buf, len, "-0.%09u", abs(tmp1));
> > + else
> > + return snprintf(buf, len, "%d.%09u", tmp0,
> abs(tmp1));
> > case IIO_VAL_FRACTIONAL_LOG2:
> > tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
> > tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);
