LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
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: Thu, 29 Jul 2021 12:19:11 -0400	[thread overview]
Message-ID: <CD5RDQA6H2AZ.3R2031X2O3BWK@shaak> (raw)
In-Reply-To: <4e477a42-1cae-06f8-2778-fc734359d6f3@axentia.se>

On Wed Jul 28, 2021 at 3:58 AM EDT, Peter Rosin wrote:
> On 2021-07-28 02:26, Liam Beguin wrote:
> > 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?
>
> Why drop the tests? Are they doing any harm? Or are they testing exactly
> the problem situation that fail without this patch?

They are testing this problem and fail without the patch.

>
> In that case, I guess fix the tests to pass and preferably add tests
> for the *val2 is "large" situation (that this patch breaks) so that the
> next person trying to improve precision is made aware of the overflow
> problem. Does that make sense?

To handle large values of *val2, I could use the same logic as in
IIO_VAL_FRACTIONAL with check_mul_overflow() and gcd().

would that be okay?

Thanks,
Liam

>
> Cheers,
> Peter
>
> > 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:[~2021-07-29 16:19 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
2021-07-28  7:58       ` Peter Rosin
2021-07-29 16:19         ` Liam Beguin [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CD5RDQA6H2AZ.3R2031X2O3BWK@shaak \
    --to=liambeguin@gmail.com \
    --cc=devicetree@vger.kernel.org \
    --cc=jic23@kernel.org \
    --cc=lars@metafoo.de \
    --cc=linux-iio@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=peda@axentia.se \
    --cc=pmeerw@pmeerw.net \
    --cc=robh+dt@kernel.org \
    --subject='Re: [PATCH v6 09/13] iio: afe: rescale: fix precision on fractional log scale' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).