linux-kernel - Re: [PATCH v2 2/3] iio: light: Add support for AL3000a illuminance sensor

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Message-ID: <CAPVz0n2s1mxuheAadhFMHnmm6DtdMYzLHaBQDB_TEF--tWktrw@mail.gmail.com>
Date: Sun, 16 Feb 2025 16:47:52 +0200
From: Svyatoslav Ryhel <clamor95@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: David Heidelberg <david@...t.cz>, Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Thierry Reding <thierry.reding@...il.com>, Jonathan Hunter <jonathanh@...dia.com>, 
	Javier Carrasco <javier.carrasco.cruz@...il.com>, Matti Vaittinen <mazziesaccount@...il.com>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Emil Gedenryd <emil.gedenryd@...s.com>, 
	Arthur Becker <arthur.becker@...tec.com>, Mudit Sharma <muditsharma.info@...il.com>, 
	Per-Daniel Olsson <perdaniel.olsson@...s.com>, Subhajit Ghosh <subhajit.ghosh@...aklogic.com>, 
	Ivan Orlov <ivan.orlov0322@...il.com>, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2 2/3] iio: light: Add support for AL3000a illuminance sensor

нд, 16 лют. 2025 р. о 16:44 Jonathan Cameron <jic23@...nel.org> пише:
>
>
> > > > +
> > > > +static int al3000a_read_raw(struct iio_dev *indio_dev,
> > > > +                         struct iio_chan_spec const *chan, int *val,
> > > > +                         int *val2, long mask)
> > > > +{
> > > > +     struct al3000a_data *data = iio_priv(indio_dev);
> > > > +     int ret, gain;
> > > > +
> > > > +     switch (mask) {
> > > > +     case IIO_CHAN_INFO_RAW:
> > > > +             ret = regmap_read(data->regmap, AL3000A_REG_DATA, &gain);
> > > > +             if (ret < 0)
> > > > +                     return ret;
> > > > +
> > > > +             *val = lux_table[gain & AL3000A_GAIN_MASK];
> > >
> > > Why did you chosen to do post-processing in the RAW channel instead
> > > doing it in INFO_SCALE (same as al3010 does)?
> > >
> >
> > From my observation INFO_SCALE will just perform multiplication of RAW
> > to SCALE. In this case values which are read are not actual raw values
> > of illumination. Next is my assumption (since there is no datasheet),
> > but values obtained from register are similar to values from adc
> > thermal sensors, they need be converted via reference table to get
> > actual data.
>
> Please add a comment somewhere here to say that we don't know the
> relationship of these values to illuminance hence providing
> _RAW and _SCALE would not be helpful.
>

We do know relationship of these values to illuminance thanks to
conversion table provided.

> >
> > > Except this, LGTM.
> > >
> > > Documentation and DT patch:
> > >
> > > Reviewed-by: David Heidelberg <david@...t.cz>
> > > > +
> > > > +             return IIO_VAL_INT;
> > > > +     case IIO_CHAN_INFO_SCALE:
> > > > +             *val = 1;
> > > > +
>
> Don't do this.  The above lack of known relationship has to be
> expressed by not providing the _scale attribute.
>
> > > > +             return IIO_VAL_INT;
> > > > +     default:
> > > > +             return -EINVAL;
> > > > +     }
> > > > +}
> > > > +
> > > > +static const struct iio_info al3000a_info = {
> > > > +     .read_raw       = al3000a_read_raw,
> > > > +};
>
>