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

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Date:   Sun, 29 Aug 2021 15:35:39 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Liam Beguin <liambeguin@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        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, 16 Aug 2021 16:12:58 +0300
Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Mon, Aug 16, 2021 at 4:07 PM Liam Beguin <liambeguin@...il.com> wrote:
> > On Mon Aug 16, 2021 at 8:48 AM EDT, Andy Shevchenko wrote:  
> > > On Mon, Aug 16, 2021 at 3:39 PM Liam Beguin <liambeguin@...il.com>
> > > wrote:  
> > > > 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:  
> 
> ...
> 
> > > > > > +       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.  
> > >
> > > Don't assign and don't check the error code of the API. As simply as
> > > that.  
> >
> > I'm not against getting rid of it, but I was asked to check for these
> > errors in earlier revisions of the patch.  
> 
> Okay, I leave it to you, guys, to decide, just note that the usual
> pattern for optional stuff
> a) either check for (!ret);
> b) or ignore the returned value completely.

Hmm. My thinking (I suspect I asked for it to be checked, but can't remember :)
was that I'd really like to know if a device tree contains a property but that
property is invalid for some reason. The docs give a bunch of reasons beyond
the property not existing (which is unhelpfully described as just 'invalid parameters'). 

I guess that's a bit far fetched.  Let's drop the check as Andy suggests.

Dropped that check and applied to the togreg branch of iio.git, initially pushed out
as testing for 0-day to poke at it.  + we are about to enter merge window so I don't
want linux-next to pick it up just yet!

Jonathan

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