linux-kernel - Re: [PATCH v9 05/14] iio: afe: rescale: add INT_PLUS

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Date:   Sun, 21 Nov 2021 11:11:29 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Liam Beguin <liambeguin@...il.com>
Cc:     peda@...ntia.se, lars@...afoo.de, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        robh+dt@...nel.org
Subject: Re: [PATCH v9 05/14] iio: afe: rescale: add INT_PLUS_{MICRO,NANO}
 support

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

> From: Liam Beguin <lvb@...hos.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@...hos.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;