linux-kernel - Re: [PATCH v4 2/2] iio: adc: ad7944: add driver for AD7944/AD7985/AD7986

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Date: Mon, 4 Mar 2024 08:28:52 -0600
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: linux-iio@...r.kernel.org, 
	Michael Hennerich <Michael.Hennerich@...log.com>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Nuno Sá <nuno.sa@...log.com>, 
	Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] iio: adc: ad7944: add driver for AD7944/AD7985/AD7986

On Sun, Mar 3, 2024 at 7:44 AM Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Thu, 29 Feb 2024 10:25:51 -0600
> David Lechner <dlechner@...libre.com> wrote:
>
> > This adds a driver for the Analog Devices Inc. AD7944, AD7985, and
> > AD7986 ADCs. These are a family of pin-compatible ADCs that can sample
> > at rates up to 2.5 MSPS.
> >
> > The initial driver adds support for sampling at lower rates using the
> > usual IIO triggered buffer and can handle all 3 possible reference
> > voltage configurations.
> >
> > Signed-off-by: David Lechner <dlechner@...libre.com>
> >
> Hi David,
>
> Fresh read through showed up a few more things.  They are all trivial except
> for what I think is an inverted error condition which would break
> cases where ref was not supplied in DT.

Thanks. All suggestions seems reasonable to me.

> >
> > +
> > +     /*
> > +      * Sort out what is being used for the reference voltage. Options are:
> > +      * - internal reference: neither REF or REFIN is connected
> > +      * - internal reference with external buffer: REF not connected, REFIN
> > +      *   is connected
> > +      * - external reference: REF is connected, REFIN is not connected
> > +      */
> > +
> > +     ref = devm_regulator_get_optional(&spi->dev, "ref");
> > +     if (IS_ERR(ref)) {
> > +             if (PTR_ERR(ref) != -ENODEV)
>
> Confused. Isn't this inverse of what we want?

Yes, thanks for catching.

> return an error if we got anything other than -ENODEV.
>                 if (PTR_ERR(ref) |= -ENODEV)
>                         return dev_err_probe(&spi->dev, PTR_ERR(ref),
>                                              "failed to get REF supply\n");
>                 ref = NULL;
>         }
>
> > +                     ref = NULL;
> > +             else
> > +                     return dev_err_probe(&spi->dev, PTR_ERR(ref),
> > +                                          "failed to get REF supply\n");
> > +     }
> > +
>
> > +
> > +     adc->cnv = devm_gpiod_get(&spi->dev, "cnv", GPIOD_OUT_LOW);
> > +     if (IS_ERR(adc->cnv))
> > +             return dev_err_probe(&spi->dev, PTR_ERR(adc->cnv),
> > +                                  "failed to get CNV GPIO\n");
>
> Is this optional?  If we don't yet support the case the dt binding talks
> about worth a comment here to say we don't yet support XYZ so this
> is not optional.

For now, it is required since we have only implemented 4-wire mode.