[PATCH] drivers: iio: pressure: dps310: Fix failure to read negative numbers

[George Liu]

On Thu, Feb 1, 2024 at 4:32 PM Paul Menzel <pmenzel at molgen.mpg.de> wrote:
>
> Dear George,
>
>
> Thank you for your patch.
>
>
> Am 01.02.24 um 09:25 schrieb George Liu:
> > The dps310 chip driver fails to read the temperature when the
> > temperature reaches below zero.
>
> Stating, how you fixed this would also be nice.
>
> How did you test this?

Updated.

>
> > Signed-off-by: George Liu <liuxiwei at ieisystem.com>
> > ---
> >   drivers/iio/pressure/dps310.c | 9 +++++----
> >   1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/iio/pressure/dps310.c b/drivers/iio/pressure/dps310.c
> > index 1ff091b2f764..fcbfdc5e85b7 100644
> > --- a/drivers/iio/pressure/dps310.c
> > +++ b/drivers/iio/pressure/dps310.c
> > @@ -730,7 +730,7 @@ static int dps310_read_pressure(struct dps310_data *data, int *val, int *val2,
> >       }
> >   }
> >
> > -static int dps310_calculate_temp(struct dps310_data *data)
> > +static int dps310_calculate_temp(struct dps310_data *data, int *val)
> >   {
> >       s64 c0;
> >       s64 t;
> > @@ -746,7 +746,9 @@ static int dps310_calculate_temp(struct dps310_data *data)
> >       t = c0 + ((s64)data->temp_raw * (s64)data->c1);
> >
> >       /* Convert to milliCelsius and scale the temperature */
> > -     return (int)div_s64(t * 1000LL, kt);
> > +     *val = (int)div_s64(t * 1000LL, kt);
> > +
> > +     return 0;
> >   }
>
> This works, because `dps310_get_temp_k` returns the temperature in
> Kelvin which cannot be negative?

dps310_get_temp_k is correct, the problem is
`return (int)div_s64(t * 1000LL, kt);`

If it reaches below 0 degrees, a negative number will definitely be
returned here.
Then in the dps310_read_temp method, `val` will not be assigned a
value, but rc will be returned directly;

>
>      static int dps310_get_temp_k(struct dps310_data *data)
>      {
>              int rc = dps310_get_temp_precision(data);
>
>              if (rc < 0)
>                      return rc;
>
>              return scale_factors[ilog2(rc)];
>      }
>
>
> Kind regards,
>
> Paul
>
> >   static int dps310_read_temp(struct dps310_data *data, int *val, int *val2,
> > @@ -768,11 +770,10 @@ static int dps310_read_temp(struct dps310_data *data, int *val, int *val2,
> >               if (rc)
> >                       return rc;
> >
> > -             rc = dps310_calculate_temp(data);
> > +             rc = dps310_calculate_temp(data, val);
> >               if (rc < 0)
> >                       return rc;
> >
> > -             *val = rc;
> >               return IIO_VAL_INT;
> >
> >       case IIO_CHAN_INFO_OVERSAMPLING_RATIO: