LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Peter Rosin <peda@axentia.se>
To: Liam Beguin <liambeguin@gmail.com>,
	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: Wed, 28 Jul 2021 09:58:10 +0200	[thread overview]
Message-ID: <4e477a42-1cae-06f8-2778-fc734359d6f3@axentia.se> (raw)
In-Reply-To: <CD4CHX6R9QRI.2Q76MYJGTXNWK@shaak>

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?

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?

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:[~2021-07-28  7:58 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 [this message]
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

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=4e477a42-1cae-06f8-2778-fc734359d6f3@axentia.se \
    --to=peda@axentia.se \
    --cc=devicetree@vger.kernel.org \
    --cc=jic23@kernel.org \
    --cc=lars@metafoo.de \
    --cc=liambeguin@gmail.com \
    --cc=linux-iio@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --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).