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 v4 05/10] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
Date: Fri, 09 Jul 2021 15:30:23 -0400 [thread overview]
Message-ID: <CCOUX814CQ6U.XY2CIQKFE00V@shaak> (raw)
In-Reply-To: <4be51a74-9913-291a-9dac-422ac23da3ea@axentia.se>
On Fri Jul 9, 2021 at 12:29 PM EDT, Peter Rosin wrote:
>
>
> On 2021-07-06 18:09, Liam Beguin wrote:
> > From: Liam Beguin <lvb@xiphos.com>
> >
> > Add IIO_VAL_INT_PLUS_{NANO,MICRO} scaling support.
> > Scale the integer part and the decimal parts individually and keep the
> > original scaling type.
> >
> > Signed-off-by: Liam Beguin <lvb@xiphos.com>
> > ---
> > drivers/iio/afe/iio-rescale.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> > index ba3bdcc69b16..1d0e24145d87 100644
> > --- a/drivers/iio/afe/iio-rescale.c
> > +++ b/drivers/iio/afe/iio-rescale.c
> > @@ -89,7 +89,15 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
> > do_div(tmp, 1000000000LL);
> > *val = tmp;
> > return ret;
> > + case IIO_VAL_INT_PLUS_NANO:
> > + case IIO_VAL_INT_PLUS_MICRO:
> > + tmp = (s64)*val * rescale->numerator;
> > + *val = div_s64(tmp, rescale->denominator);
> > + tmp = (s64)*val2 * rescale->numerator;
> > + *val2 = div_s64(tmp, rescale->denominator);
>
Hi Peter,
> Hi!
>
> You are losing precision, and you are not mormalising after the
> calculation.
Can you elaborate a little on what you mean here?
Do you mean that I should make sure that *val2, the PLUS_{NANO,MICRO}
part, doesn't contain an integer part? And if so transfer that part back
to *val?
> I think it's better to not even attempt this given that the results can
> be
> really poor.
Unfortunatelly, I'm kinda stuck with this as some of my ADC use these
types.
Thanks,
Liam
>
> Cheers,
> Peter
>
> > + return ret;
> > default:
> > + dev_err(&indio_dev->dev, "unsupported type %d\n", ret);
> > return -EOPNOTSUPP;
> > }
> > default:
> >
next prev parent reply other threads:[~2021-07-09 19:30 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-06 16:09 [PATCH v4 00/10] iio: afe: add temperature rescaling support Liam Beguin
2021-07-06 16:09 ` [PATCH v4 01/10] iio: inkern: apply consumer scale on IIO_VAL_INT cases Liam Beguin
2021-07-06 16:09 ` [PATCH v4 02/10] iio: inkern: apply consumer scale when no channel scale is available Liam Beguin
2021-07-06 16:09 ` [PATCH v4 03/10] iio: inkern: make a best effort on offset calculation Liam Beguin
2021-07-06 16:09 ` [PATCH v4 04/10] iio: afe: rescale: reduce risk of integer overflow Liam Beguin
2021-07-09 16:24 ` Peter Rosin
2021-07-09 19:22 ` Liam Beguin
2021-07-06 16:09 ` [PATCH v4 05/10] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support Liam Beguin
2021-07-09 16:29 ` Peter Rosin
2021-07-09 19:30 ` Liam Beguin [this message]
2021-07-10 8:14 ` Peter Rosin
2021-07-10 17:45 ` Liam Beguin
2021-07-06 16:09 ` [PATCH v4 06/10] iio: afe: rescale: add offset support Liam Beguin
2021-07-06 16:09 ` [PATCH v4 07/10] iio: afe: rescale: add RTD temperature sensor support Liam Beguin
2021-07-06 16:09 ` [PATCH v4 08/10] iio: afe: rescale: add temperature transducers Liam Beguin
2021-07-06 16:09 ` [PATCH v4 09/10] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Liam Beguin
2021-07-12 16:08 ` Rob Herring
2021-07-06 16:09 ` [PATCH v4 10/10] dt-bindings: iio: afe: add bindings for temperature transducers Liam Beguin
2021-07-12 16:11 ` Rob Herring
2021-07-13 4:20 ` Liam Beguin
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