linux-kernel - Re: [PATCH v2] iio: adc: ad4170-4: Use ERR_PTR() with %pe to improve error logging

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Message-ID: <CAHp75VfEC3qUurUO4LKA1d6_Ot15AHY2zG9tk3wWrtYAgHrHgQ@mail.gmail.com>
Date: Thu, 7 Aug 2025 23:02:58 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: David Lechner <dlechner@...libre.com>
Cc: Salah Triki <salah.triki@...il.com>, Lars-Peter Clausen <lars@...afoo.de>, 
	Michael Hennerich <Michael.Hennerich@...log.com>, Marcelo Schmitt <marcelo.schmitt@...log.com>, 
	Jonathan Cameron <jic23@...nel.org>, Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iio: adc: ad4170-4: Use ERR_PTR() with %pe to improve
 error logging

On Thu, Aug 7, 2025 at 11:01 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Thu, Aug 7, 2025 at 6:03 PM David Lechner <dlechner@...libre.com> wrote:
> > On 8/7/25 3:05 AM, Salah Triki wrote:

...

> > >       ret = __ad4170_read_sample(indio_dev, chan, val);
> > >       if (ret) {
> > > -             dev_err(dev, "failed to read sample: %d\n", ret);
> > > +             dev_err(dev, "failed to read sample: %pe\n", ERR_PTR(ret));
> > >
> > >               ret2 = ad4170_set_channel_enable(st, chan->address, false);
> > >               if (ret2)
> > > -                     dev_err(dev, "failed to disable channel: %d\n", ret2);
> > > +                     dev_err(dev, "failed to disable channel: %pe\n", ERR_PTR(ret2));
> > >
> > >               return ret;
> > >       }
> >
> > Interesting, I didn't know we had this format specifier. But I think
> > this is something we would want to do kernel-wide or not at all to stay
> > consistent.
>
> I'm sorry but I didn't follow. This is a kernel-wide format specifier.
>
> > And if we are doing this in more places, it would make sense to have a new
> > format specifier for integer error values instead of casting them to
> > pointers.
>
> Will _very unlikely_ to happen. This has to be a C standard for that,
> otherwise you are suggesting to always have a kernel warning for each
> of these cases. The only way we can customize specifiers w/o
> introducing a compiler warnings is to continue (and still carefully)
> using %p extensions.

And to be clear: I am not in favour of this change exactly due to a
bit weird (for the reader) castings just for the sake of use of %pe.


-- 
With Best Regards,
Andy Shevchenko