linux-kernel - Re: [PATCH] staging: pi433: remove unnecessary parentheses

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Date:   Tue, 09 Jan 2018 11:42:16 -0800
From:   Joe Perches <joe@...ches.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Valentin Vidic <Valentin.Vidic@...Net.hr>,
        David Miller <davem@...emloft.net>, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org,
        Marcin Ciupak <marcin.s.ciupak@...il.com>,
        Marcus Wolf <linux@...f-entwicklungen.de>,
        Simon Sandström <simon@...anor.nu>
Subject: Re: [PATCH] staging: pi433: remove unnecessary parentheses

On Tue, 2018-01-09 at 20:28 +0100, Greg Kroah-Hartman wrote:
> On Tue, Jan 09, 2018 at 11:21:37AM -0800, Joe Perches wrote:
> > On Tue, 2018-01-09 at 15:31 +0100, Greg Kroah-Hartman wrote:
> > > On Mon, Jan 08, 2018 at 06:38:55PM +0100, Valentin Vidic wrote:
> > > > Fixes checkpatch warnings:
> > > >   CHECK: Unnecessary parentheses around 'mantisse != mantisse16'
> > > >   CHECK: Unnecessary parentheses around 'mantisse != mantisse20'
> > > >   CHECK: Unnecessary parentheses around 'mantisse != mantisse24'
> > 
> > []
> > > > diff --git a/drivers/staging/pi433/rf69.c b/drivers/staging/pi433/rf69.c
> > 
> > []
> > > > @@ -391,9 +391,9 @@ static int rf69_set_bandwidth_intern(struct spi_device *spi, u8 reg,
> > > >  		return -EINVAL;
> > > >  	}
> > > >  
> > > > -	if ((mantisse != mantisse16) &&
> > > > -	    (mantisse != mantisse20) &&
> > > > -	    (mantisse != mantisse24)) {
> > > > +	if (mantisse != mantisse16 &&
> > > > +	    mantisse != mantisse20 &&
> > > > +	    mantisse != mantisse24) {
> > > 
> > > I'm getting really tired of seeing this checkpatch warning, when it's a
> > > major pain.
> > 
> > Your idea of major pain and mine differ a bit.
> 
> I don't like taking patches that cause future problems.

What future problems might this particular case present
that isn't generic in all patches.

> > > Joe, can you please turn these off.  Patches like this will force people
> > > to have to remember that != is higher precidence than &&.
> > 
> > As it's not just 1 precedence level but 4 and 5, it
> > really shouldn't be that hard to remember.
> 
> I can't remember any of them, and I should not have to.

That depends on how well you know your C.

>   That's the
> point, you should not assume anyone knows the levels, code is written
> for developers to understand first, and the compiler second.

And someone that knows C knows those levels and the parentheses
can just be visual noise requiring extra thought.

Sometimes it's useful, sometimes it's not.

	if (a == b && c == d)

is pretty trivial.

and I believe

	if ((a == b))

emits clang warnings

>   By
> removing these, it doesn't do anything for the compiler, but makes the
> developer think longer about them.

Generally I have to think more with more parentheses.

> > > The original code here was just fine.
> > 
> > And I don't really disagree with you.
> > 
> > David Miller has a preference for the parenthesis free
> > style. I believe he mentioned it sometime in August 2017
> > but I can't find it right now.
> > 
> > Anyway, perhaps
> > ---
> >  scripts/checkpatch.pl | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > index d2464058ab5d..3a7499de2c2d 100755
> > --- a/scripts/checkpatch.pl
> > +++ b/scripts/checkpatch.pl
> > @@ -4526,7 +4526,9 @@ sub process {
> >  		}
> >  
> >  # check for unnecessary parentheses around comparisons in if uses
> > -		if ($^V && $^V ge 5.10.0 && defined($stat) &&
> > +# when !drivers/staging or the command-line uses --strict
> > +		if (($realfile !~ m@^(?:drivers/staging/)@ || $check_orig) &&
> > +		    $^V && $^V ge 5.10.0 && defined($stat) &&
> 
> How about only if in the networking area?  I don't want to take patches
> for this for other parts of the kernel either, it's really useless.

AFAIK: Almost no one thinks when sending staging patches.

For other parts of the tree, it requires --strict on the
command line.  AFAIK: almost no one uses that and if they
do, then they can determine for themselves if they want
to remove excessive parentheses.