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 v4 05/10] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
Date: Fri, 9 Jul 2021 18:29:15 +0200 [thread overview]
Message-ID: <4be51a74-9913-291a-9dac-422ac23da3ea@axentia.se> (raw)
In-Reply-To: <20210706160942.3181474-6-liambeguin@gmail.com>
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!
You are losing precision, and you are not mormalising after the calculation.
I think it's better to not even attempt this given that the results can be
really poor.
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 16:29 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 [this message]
2021-07-09 19:30 ` Liam Beguin
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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