linux-kernel - Re: [PATCH v8 05/14] iio: afe: rescale: add INT_PLUS

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Date:   Sat, 28 Aug 2021 22:50:53 -0400
From:   Liam Beguin <liambeguin@...il.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     jic23@...nel.org, lars@...afoo.de, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        robh+dt@...nel.org
Subject: Re: [PATCH v8 05/14] iio: afe: rescale: add INT_PLUS_{MICRO,NANO}
 support

On Thu, Aug 26, 2021 at 10:11:18AM +0200, Peter Rosin wrote:
> On 2021-08-20 21:17, Liam Beguin 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 | 35 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 35 insertions(+)
> > 
> > diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> > index d0669fd8eac5..8488f1d83527 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 +43,38 @@ 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;
> > +		/*
> > +		 * For IIO_VAL_INT_PLUS_{MICRO,NANO} scale types if *val OR
> > +		 * *val2 is negative the schan scale is negative
> 
> The last line doesn't parse for me. It doesn't end with a period either, so
> it looks like you moved on before you finished it?

I meant to warn that IIO_VAL_INT_PLUS_{MICRO,NANO} are a little odd, and
that if either one *val or *val2 is negative, the result will be
negative.

i.e. *val = 1 and *val2 = -0.5 gives -1.5 and not 0.5.

I'll give it another try and will add the period.

Thanks,
Liam

> 
> Cheers,
> Peter
> 
> > +		 */
> > +		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;
> >