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    SubjectRe: [PATCH v4 05/10] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
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    On 2021-07-06 18:09, Liam Beguin wrote:
    > From: Liam Beguin <lvb@xiphos.com>
    >
    > Add IIO_VAL_INT_PLUS_{NANO,MICRO} scaling support.
    > Scale the integer part and the decimal parts individually and keep the
    > original scaling type.
    >
    > Signed-off-by: Liam Beguin <lvb@xiphos.com>
    > ---
    > drivers/iio/afe/iio-rescale.c | 8 ++++++++
    > 1 file changed, 8 insertions(+)
    >
    > diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
    > index ba3bdcc69b16..1d0e24145d87 100644
    > --- a/drivers/iio/afe/iio-rescale.c
    > +++ b/drivers/iio/afe/iio-rescale.c
    > @@ -89,7 +89,15 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
    > do_div(tmp, 1000000000LL);
    > *val = tmp;
    > return ret;
    > + case IIO_VAL_INT_PLUS_NANO:
    > + case IIO_VAL_INT_PLUS_MICRO:
    > + tmp = (s64)*val * rescale->numerator;
    > + *val = div_s64(tmp, rescale->denominator);
    > + tmp = (s64)*val2 * rescale->numerator;
    > + *val2 = div_s64(tmp, rescale->denominator);

    Hi!

    You are losing precision, and you are not mormalising after the calculation.
    I think it's better to not even attempt this given that the results can be
    really poor.

    Cheers,
    Peter

    > + return ret;
    > default:
    > + dev_err(&indio_dev->dev, "unsupported type %d\n", ret);
    > return -EOPNOTSUPP;
    > }
    > default:
    >

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