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Message-ID: <20251015144019.GA2207492@legfed1>
Date: Wed, 15 Oct 2025 16:40:19 +0200
From: Dimitri Fedrau <dima.fedrau@...il.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: dimitri.fedrau@...bherr.com,
Javier Carrasco <javier.carrasco.cruz@...il.com>,
Li peiyu <579lpy@...il.com>, Jonathan Cameron <jic23@...nel.org>,
David Lechner <dlechner@...libre.com>,
Nuno Sá <nuno.sa@...log.com>,
Andy Shevchenko <andy@...nel.org>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
Chris Lesiak <chris.lesiak@...orbio.com>
Subject: Re: [PATCH v3 2/2] iio: humditiy: hdc3020: fix units for thresholds
and hysteresis
Am Wed, Oct 15, 2025 at 12:45:31PM +0300 schrieb Andy Shevchenko:
> On Mon, Oct 13, 2025 at 11:12 AM Dimitri Fedrau via B4 Relay
> <devnull+dimitri.fedrau.liebherr.com@...nel.org> wrote:
> >
> > According to the ABI the units after application of scale and offset are
> > milli degree celsius for temperature thresholds and milli percent for
> > relative humidity thresholds. Currently the resulting units are degree
> > celsius for temperature thresholds and hysteresis and percent for relative
> > humidity thresholds and hysteresis. Change scale factor to fix this issue.
>
> ...
>
>
> > - return -2949075 + (175 * temp);
> > + return -589815 + (35 * temp);
>
> I was under the impression that we agreed on the explicit division by 5.
>
> return -2949075 / 5 + (175 / 5 * temp);
>
I wanted to scale the formula as it has been done before, but didn't make
it really clear. After thinking about it again, I think you are right,
will add the explicit division by 5.
> ...
>
> > - return hum * 100;
> > + return hum * 20;
>
> And in a similar way here.
>
Ok.
>
> > s_clr = max(s_clr, HDC3020_MIN_TEMP_MICRO);
> > s_clr = min(s_clr, HDC3020_MAX_TEMP_MICRO);
> > @@ -565,7 +574,8 @@ static int hdc3020_write_thresh(struct iio_dev *indio_dev,
> > /* Calculate old hysteresis */
> > s_thresh = (s64)hdc3020_thresh_get_hum(thresh) * 1000000;
> > s_clr = (s64)hdc3020_thresh_get_hum(clr) * 1000000;
> > - s_hyst = div_s64(abs(s_thresh - s_clr), 65535);
> > + s_hyst = div_s64(abs(s_thresh - s_clr),
> > + HDC3020_THRESH_FRACTION);
> > /* Set new threshold */
> > thresh = reg_val;
> > /* Try to set old hysteresis */
> > @@ -574,15 +584,16 @@ static int hdc3020_write_thresh(struct iio_dev *indio_dev,
> > case IIO_EV_INFO_HYSTERESIS:
> > /*
> > * Function hdc3020_thresh_get_hum returns relative
> > - * humidity in percent scaled by 65535. Scale by 1000000
> > - * to be able to subtract scaled hysteresis value.
> > + * humidity in percent scaled by HDC3020_THRESH_FRACTION.
> > + * Scale by 1000000 to be able to subtract scaled
> > + * hysteresis value.
> > */
> > s_thresh = (s64)hdc3020_thresh_get_hum(thresh) * 1000000;
> > /*
> > - * Units of s_val are in micro percent, scale by 65535
> > - * to get same units as s_thresh.
> > + * Units of s_val are in micro percent, scale by
> > + * HDC3020_THRESH_FRACTION to get same units as s_thresh.
> > */
> > - s_hyst = (s64)s_val * 65535;
> > + s_hyst = (s64)s_val * HDC3020_THRESH_FRACTION;
> > s_clr = hdc3020_thresh_clr(s_thresh, s_hyst, dir);
> > s_clr = max(s_clr, 0);
> > s_clr = min(s_clr, HDC3020_MAX_HUM_MICRO);
> > @@ -630,7 +641,7 @@ static int hdc3020_read_thresh(struct iio_dev *indio_dev,
> > thresh = hdc3020_thresh_get_temp(ret);
> > switch (info) {
> > case IIO_EV_INFO_VALUE:
> > - *val = thresh;
> > + *val = thresh * MILLI;
> > break;
> > case IIO_EV_INFO_HYSTERESIS:
> > ret = hdc3020_read_be16(data, reg_clr);
> > @@ -638,18 +649,18 @@ static int hdc3020_read_thresh(struct iio_dev *indio_dev,
> > return ret;
> >
> > clr = hdc3020_thresh_get_temp(ret);
> > - *val = abs(thresh - clr);
> > + *val = abs(thresh - clr) * MILLI;
> > break;
> > default:
> > return -EOPNOTSUPP;
> > }
> > - *val2 = 65535;
> > + *val2 = HDC3020_THRESH_FRACTION;
> > return IIO_VAL_FRACTIONAL;
> > case IIO_HUMIDITYRELATIVE:
> > thresh = hdc3020_thresh_get_hum(ret);
> > switch (info) {
> > case IIO_EV_INFO_VALUE:
> > - *val = thresh;
> > + *val = thresh * MILLI;
> > break;
> > case IIO_EV_INFO_HYSTERESIS:
> > ret = hdc3020_read_be16(data, reg_clr);
> > @@ -657,12 +668,12 @@ static int hdc3020_read_thresh(struct iio_dev *indio_dev,
> > return ret;
> >
> > clr = hdc3020_thresh_get_hum(ret);
> > - *val = abs(thresh - clr);
> > + *val = abs(thresh - clr) * MILLI;
> > break;
> > default:
> > return -EOPNOTSUPP;
> > }
> > - *val2 = 65535;
> > + *val2 = HDC3020_THRESH_FRACTION;
> > return IIO_VAL_FRACTIONAL;
> > default:
> > return -EOPNOTSUPP;
> >
> > --
> > 2.39.5
> >
> >
>
>
Best regards,
Dimitri Fedrau
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