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From: "Liam Beguin" <liambeguin@gmail.com>
To: "Peter Rosin" <peda@axentia.se>, <jic23@kernel.org>,
	<lars@metafoo.de>, <pmeerw@pmeerw.net>
Cc: <linux-kernel@vger.kernel.org>, <linux-iio@vger.kernel.org>,
	<devicetree@vger.kernel.org>, <robh+dt@kernel.org>
Subject: Re: [PATCH v6 09/13] iio: afe: rescale: fix precision on fractional log scale
Date: Tue, 27 Jul 2021 20:26:43 -0400	[thread overview]
Message-ID: <CD4CHX6R9QRI.2Q76MYJGTXNWK@shaak> (raw)
In-Reply-To: <d2dea8ea-5a31-0428-4eac-4e4315d07a42@axentia.se>

On Fri Jul 23, 2021 at 5:20 PM EDT, Peter Rosin wrote:
> On 2021-07-21 05:06, Liam Beguin wrote:
> > From: Liam Beguin <lvb@xiphos.com>
> > 
> > The IIO_VAL_FRACTIONAL_LOG2 scale type doesn't return the expected
> > scale. Update the case so that the rescaler returns a fractional type
> > and a more precise scale.
> > 
> > Signed-off-by: Liam Beguin <lvb@xiphos.com>
> > ---
> >  drivers/iio/afe/iio-rescale.c | 9 +++------
> >  1 file changed, 3 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> > index 35fa3b4e53e0..47cd4a6d9aca 100644
> > --- a/drivers/iio/afe/iio-rescale.c
> > +++ b/drivers/iio/afe/iio-rescale.c
> > @@ -44,12 +44,9 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
> >  		*val2 = rescale->denominator;
> >  		return IIO_VAL_FRACTIONAL;
> >  	case IIO_VAL_FRACTIONAL_LOG2:
> > -		tmp = *val * 1000000000LL;
> > -		do_div(tmp, rescale->denominator);
> > -		tmp *= rescale->numerator;
> > -		do_div(tmp, 1000000000LL);
> > -		*val = tmp;
> > -		return scale_type;
> > +		*val = rescale->numerator * *val;
> > +		*val2 = rescale->denominator * (1 << *val2);
> > +		return IIO_VAL_FRACTIONAL;
>
> Hi!

Hi Peter,

>
> I do not think this is an uncontested improvement. You have broken the
> case
> where *val2 is "large" before the scale factor is applied.

I was a little reluctant to add this change as I keep increasing the
scope of this series, but since I added tests for all cases, I didn't
want to leave this one out.

Would you rather I drop this patch and the test cases associated to it?

Thanks,
Liam

>
> Cheers,
> Peter
>
> >  	case IIO_VAL_INT_PLUS_NANO:
> >  		tmp = ((s64)*val * 1000000000LL + *val2) * rescale->numerator;
> >  		tmp = div_s64(tmp, rescale->denominator);
> > 


  reply	other threads:[~2021-07-28  0:26 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-21  3:06 [PATCH v6 00/13] iio: afe: add temperature rescaling support Liam Beguin
2021-07-21  3:06 ` [PATCH v6 01/13] iio: inkern: apply consumer scale on IIO_VAL_INT cases Liam Beguin
2021-07-21  3:06 ` [PATCH v6 02/13] iio: inkern: apply consumer scale when no channel scale is available Liam Beguin
2021-07-21  3:06 ` [PATCH v6 03/13] iio: inkern: make a best effort on offset calculation Liam Beguin
2021-07-21  3:06 ` [PATCH v6 04/13] iio: afe: rescale: expose scale processing function Liam Beguin
2021-07-21  3:06 ` [PATCH v6 05/13] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support Liam Beguin
2021-07-23 21:16   ` Peter Rosin
2021-07-28  0:21     ` Liam Beguin
2021-07-28  7:19       ` Peter Rosin
2021-07-29 15:56         ` Liam Beguin
2021-07-30  6:49           ` Peter Rosin
2021-07-30  7:01             ` Peter Rosin
2021-07-30 20:01               ` Liam Beguin
2021-07-30 19:57             ` Liam Beguin
2021-07-31 17:47         ` Jonathan Cameron
2021-07-21  3:06 ` [PATCH v6 06/13] iio: afe: rescale: add offset support Liam Beguin
2021-07-21  3:06 ` [PATCH v6 07/13] iio: test: add basic tests for the iio-rescale driver Liam Beguin
2021-07-24  8:40   ` kernel test robot
2021-07-21  3:06 ` [PATCH v6 08/13] iio: afe: rescale: reduce risk of integer overflow Liam Beguin
2021-07-23 21:17   ` Peter Rosin
2021-07-28  0:07     ` Liam Beguin
2021-07-28  7:47       ` Peter Rosin
2021-07-29 16:02         ` Liam Beguin
2021-07-21  3:06 ` [PATCH v6 09/13] iio: afe: rescale: fix precision on fractional log scale Liam Beguin
2021-07-23 21:20   ` Peter Rosin
2021-07-28  0:26     ` Liam Beguin [this message]
2021-07-28  7:58       ` Peter Rosin
2021-07-29 16:19         ` Liam Beguin
2021-07-21  3:06 ` [PATCH v6 10/13] iio: afe: rescale: add RTD temperature sensor support Liam Beguin
2021-07-21  3:06 ` [PATCH v6 11/13] iio: afe: rescale: add temperature transducers Liam Beguin
2021-07-21  3:06 ` [PATCH v6 12/13] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Liam Beguin
2021-07-21  3:06 ` [PATCH v6 13/13] dt-bindings: iio: afe: add bindings for temperature transducers Liam Beguin
2021-07-23 22:59   ` Rob Herring

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