Re: [PATCH v9 05/14] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support

Jonathan Cameron
2021-11-21T11:06:41Z

On Sun, 14 Nov 2021 22:43:25 -0500
Liam Beguin <liambeguin@gmail.com> wrote:

> From: Liam Beguin <lvb@xiphos.com>
>
> Some ADCs use IIO_VAL_INT_PLUS_{NANO,MICRO} scale types.
> Add support for these to allow using the iio-rescaler with them.
>
> Signed-off-by: Liam Beguin <lvb@xiphos.com>
> ---
> drivers/iio/afe/iio-rescale.c | 36 +++++++++++++++++++++++++++++++++++
> 1 file changed, 36 insertions(+)
>
> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> index d0669fd8eac5..2c25a6375f99 100644
> --- a/drivers/iio/afe/iio-rescale.c
> +++ b/drivers/iio/afe/iio-rescale.c
> @@ -22,6 +22,9 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
> int *val, int *val2)
> {
> unsigned long long tmp;
> + s32 rem;
> + u32 mult;
> + u32 neg;
>
> switch (scale_type) {
> case IIO_VAL_FRACTIONAL:
> @@ -40,6 +43,39 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
> tmp *= rescale->numerator;
> do_div(tmp, 1000000000LL);
> *val = tmp;
> + return scale_type;
> + case IIO_VAL_INT_PLUS_NANO:
> + case IIO_VAL_INT_PLUS_MICRO:
> + if (scale_type == IIO_VAL_INT_PLUS_NANO)
> + mult = 1000000000LL;
> + else
> + mult = 1000000LL;

Trivial but perhaps you can use the multipliers defined in include/linux/units.h?
mut = MICRO; etc.

I think that patch set crossed with the earlier versions of this one but given
it's now there I think it would slightly improve readability.

> + /*
> + * For IIO_VAL_INT_PLUS_{MICRO,NANO} scale types if either *val
> + * OR *val2 is negative the schan scale is negative, i.e.
> + * *val = 1 and *val2 = -0.5 yields -1.5 not -0.5.
> + */
> + neg = *val < 0 || *val2 < 0;
> +
> + tmp = (s64)abs(*val) * abs(rescale->numerator);
> + *val = div_s64_rem(tmp, abs(rescale->denominator), &rem);
> +
> + tmp = (s64)rem * mult + (s64)abs(*val2) * abs(rescale->numerator);
> + tmp = div_s64(tmp, abs(rescale->denominator));
> +
> + *val += div_s64_rem(tmp, mult, val2);
> +
> + /*
> + * If only one of the rescaler elements or the schan scale is
> + * negative, the combined scale is negative.
> + */
> + if (neg ^ ((rescale->numerator < 0) ^ (rescale->denominator < 0))) {
> + if (*val)
> + *val = -*val;
> + else
> + *val2 = -*val2;
> + }
> +
> return scale_type;
> default:
> return -EOPNOTSUPP;