linux-kernel - Re: [PATCH v6 3/5] iio: adc: ad7949: add vref selection support

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Message-Id: <CDKXZBW1JDOD.1ZXIT12Y3WK5B@shaak>
Date:   Mon, 16 Aug 2021 08:39:30 -0400
From:   "Liam Beguin" <liambeguin@...il.com>
To:     "Andy Shevchenko" <andy.shevchenko@...il.com>
Cc:     "Lars-Peter Clausen" <lars@...afoo.de>,
        "Michael Hennerich" <Michael.Hennerich@...log.com>,
        "Jonathan Cameron" <jic23@...nel.org>,
        "Charles-Antoine Couret" <charles-antoine.couret@...ensium.com>,
        Nuno Sá <Nuno.Sa@...log.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "linux-iio" <linux-iio@...r.kernel.org>,
        "devicetree" <devicetree@...r.kernel.org>,
        "Rob Herring" <robh+dt@...nel.org>
Subject: Re: [PATCH v6 3/5] iio: adc: ad7949: add vref selection support

On Mon Aug 16, 2021 at 4:04 AM EDT, Andy Shevchenko wrote:
> On Mon, Aug 16, 2021 at 12:35 AM Liam Beguin <liambeguin@...il.com>
> wrote:
> >
> > From: Liam Beguin <lvb@...hos.com>
> >
> > Add support for selecting the voltage reference from the devicetree.
> >
> > This change is required to get valid readings with all three
> > vref hardware configurations supported by the ADC.
> >
> > For instance if the ADC isn't provided with an external reference,
> > the sample request must specify an internal voltage reference to get a
> > valid reading.
>
> ...
>
> > +       /* Setup internal voltage reference */
> > +       tmp = 4096000;
> > +       ret = device_property_read_u32(dev, "adi,internal-ref-microvolt", &tmp);
>
> > +       if (ret < 0 && ret != -EINVAL) {

Hi Andy,

>
> What does this check (second part) is supposed to mean?
> The first part will make it mandatory, is it the goal?
>

device_property_read_u32() will return -EINVAL if the property isn't
found in the devicetree.

This checks for errors when the property is defined while keeping it
optional.

Liam

> > +               dev_err(dev, "invalid value for adi,internal-ref-microvolt\n");
> > +               return ret;
> > +       }
>
> --
> With Best Regards,
> Andy Shevchenko