linux-kernel - Re: [PATCH v2 9/9] iio: adc: ad4062: Add GPIO Controller support

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Message-ID: <egl65ctlz2umzcdzf7ke5c2hnd33ghudklmf4pdgnp64vnzjg3@rpqrludyv4p2>
Date: Fri, 5 Dec 2025 12:53:23 +0100
From: Jorge Marques <gastmaier@...il.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Andy Shevchenko <andriy.shevchenko@...el.com>, 
	Jorge Marques <jorge.marques@...log.com>, Lars-Peter Clausen <lars@...afoo.de>, 
	Michael Hennerich <Michael.Hennerich@...log.com>, Jonathan Cameron <jic23@...nel.org>, 
	David Lechner <dlechner@...libre.com>, Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Jonathan Corbet <corbet@....net>, Linus Walleij <linus.walleij@...aro.org>, 
	Bartosz Golaszewski <brgl@...ev.pl>, linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v2 9/9] iio: adc: ad4062: Add GPIO Controller support

On Fri, Dec 05, 2025 at 12:21:31AM +0200, Andy Shevchenko wrote:
> On Thu, Dec 4, 2025 at 11:38 PM Jorge Marques <gastmaier@...il.com> wrote:
> > On Thu, Nov 27, 2025 at 11:20:54AM +0200, Andy Shevchenko wrote:
> > > On Wed, Nov 26, 2025 at 04:55:41PM +0100, Jorge Marques wrote:
> > > > On Mon, Nov 24, 2025 at 12:40:37PM +0200, Andy Shevchenko wrote:
> > > > > On Mon, Nov 24, 2025 at 10:18:08AM +0100, Jorge Marques wrote:
> 
> ...
> 
> > > > > > +       return reg_val == AD4062_GP_STATIC_HIGH ? 1 : 0;
> > > > >
> > > > >   return !!(reg_val == AD4062_GP_STATIC_HIGH);
> > > > >
> > > > > also will work.
> > > > >
> > > >     return reg_val == AD4062_GP_STATIC_HIGH;
> > >
> > > Hmm... This will include implicit bool->int. The !! guarantees values 0 or 1,
> > > but I don't remember about implicit bool->int case.
> 
> > I don't think the implicit bool->int is an issue, grepping `return .* == .*;`
> > matches a few methods that return int.
> 
> Yes, the Q here is the value of true _always_ be promoted to 1?
> 
Hi Andy,

The relational operator result has type int (c99 6.5.9 Equality
operators); and when any scalar value is converted to _Bool, the result
is 0 if the value compares equal to 0; otherwise, the result is 1 (c99
6.3.1.2).
https://www.dii.uchile.cl/~daespino/files/Iso_C_1999_definition.pdf

No conversion warnings even when forcing _Bool type.
There are many usages like this, for example:

drivers/iio/accel/adxl313_core.c @ int adxl313_is_act_inact_ac()
drivers/iio/light/opt4060.c @ int opt4060_read_event_config()
drivers/iio/light/tsl2772.c @ int tsl2772_device_id_verify()
lib/zstd/compress/zstd_fast.c @ int ZSTD_match4Found_branch()

I cannot find many legitimate usage of relational operator with the
double negation.
  git ls-files | xargs grep -s 'return !!' | grep '=='

> > Experimenting with the _Bool type (gcc 15, clang 19, any std version),
> >
> >         int main()
> >         {
> >             int a = 1;
> >             int b = 2;
> >
> >             return (_Bool)(a == b);
> >         }
> >
> > with
> > gcc -Wall -W -pedantic -std=c23 -c test.c
> > clang -Wall -Wextra -Wbool-conversion -std=c11 -O2 test.c
> >
> > also doesn't raise warnings.
> 
> Of course, because before even looking into warnings the entire code
> degrades to return 0. I.o.w., the test case is not correct. But don't
> hurry up to fix it, you won't get warnings anyway, it's all about C
> standard and not about (in)correctness of the code. See above.
> 
> -- 
> With Best Regards,
> Andy Shevchenko
Best Regards,
Jorge