linux-kernel - Re: [PATCH v2] i2c: i801: fix unused-function warning

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Message-ID: <20180515101602.79ff49cf@endymion>
Date:   Tue, 15 May 2018 10:16:02 +0200
From:   Jean Delvare <jdelvare@...e.de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Anders Roxell <anders.roxell@...aro.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] i2c: i801: fix unused-function warning

Hi Andy,

On Mon, 14 May 2018 20:18:37 +0300, Andy Shevchenko wrote:
> On Mon, May 14, 2018 at 12:33 PM, Anders Roxell
> <anders.roxell@...aro.org> wrote:
> > With CONFIG_PM, we get a harmless build warning:
> > drivers/i2c/busses/i2c-i801.c:1723:12: warning: ‘i801_resume’ defined but not used [-Wunused-function]
> >  static int i801_resume(struct device *dev)
> >             ^~~~~~~~~~~
> > drivers/i2c/busses/i2c-i801.c:1714:12: warning: ‘i801_suspend’ defined but not used [-Wunused-function]
> >  static int i801_suspend(struct device *dev)
> >             ^~~~~~~~~~~~  
> 
> > -#ifdef CONFIG_PM
> > +#ifdef CONFIG_PM_SLEEP
> >  static int i801_suspend(struct device *dev)  
> 
> The better pattern is to get rid of ugly ifdef and supply
> __maybe_unused annotation to each function in question.

That was Anders' first proposal, but it was declined by the driver
maintainer (me.) See:

https://marc.info/?l=linux-kernel&m=152588526520326&w=2

__maybe_unused is just a way to prevent the compiler from doing its
job. If it's really what you want, you might as well build with
-Wno-unused, instead of crippling the code with yet another annotation.

I can't see how building unused code only to discard it later can be
better than a proper #ifdef which will only build the code when we
actually need it.

Maybe there are cases where __maybe_unused is actually needed, but in
my opinion that should be the last resort option. That's not the case
here.

-- 
Jean Delvare
SUSE L3 Support