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[198.48.202.89]) by smtp.gmail.com with ESMTPSA id c2sm330034qtw.72.2021.07.09.12.30.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 09 Jul 2021 12:30:23 -0700 (PDT) Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 09 Jul 2021 15:30:23 -0400 Message-Id: To: "Peter Rosin" , , , Cc: , , , Subject: Re: [PATCH v4 05/10] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support From: "Liam Beguin" References: <20210706160942.3181474-1-liambeguin@gmail.com> <20210706160942.3181474-6-liambeguin@gmail.com> <4be51a74-9913-291a-9dac-422ac23da3ea@axentia.se> In-Reply-To: <4be51a74-9913-291a-9dac-422ac23da3ea@axentia.se> Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org 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 > >=20 > > Add IIO_VAL_INT_PLUS_{NANO,MICRO} scaling support. > > Scale the integer part and the decimal parts individually and keep the > > original scaling type. > >=20 > > Signed-off-by: Liam Beguin > > --- > > drivers/iio/afe/iio-rescale.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > >=20 > > diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescal= e.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_de= v, > > do_div(tmp, 1000000000LL); > > *val =3D tmp; > > return ret; > > + case IIO_VAL_INT_PLUS_NANO: > > + case IIO_VAL_INT_PLUS_MICRO: > > + tmp =3D (s64)*val * rescale->numerator; > > + *val =3D div_s64(tmp, rescale->denominator); > > + tmp =3D (s64)*val2 * rescale->numerator; > > + *val2 =3D 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: > >=20