linux-kernel - Re: [PATCH] x86/olpc: fix 'logical not is only applied to the left hand side'

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Message-ID: <YtGLkx1E8ZifiUQo@yury-laptop>
Date:   Fri, 15 Jul 2022 08:45:23 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] x86/olpc: fix 'logical not is only applied to the left
 hand side'

On Fri, Jul 15, 2022 at 05:15:36PM +0200, Alexander Lobakin wrote:
> The bitops compile-time optimization series revealed one more
> problem in olpc-xo1-sci.c:send_ebook_state(), resulted in GCC
> warnings:
> 
> arch/x86/platform/olpc/olpc-xo1-sci.c: In function 'send_ebook_state':
> arch/x86/platform/olpc/olpc-xo1-sci.c:83:63: warning: logical not is only applied to the left hand side of comparison [-Wlogical-not-parentheses]
>    83 |         if (!!test_bit(SW_TABLET_MODE, ebook_switch_idev->sw) == state)
>       |                                                               ^~
> arch/x86/platform/olpc/olpc-xo1-sci.c:83:13: note: add parentheses around left hand side expression to silence this warning
> 
> Despite this code working as intended, this redundant double
> negation of boolean value, together with comparing to `char`
> with no explicit conversion to bool, makes compilers think
> the author made some unintentional logical mistakes here.
> Make it the other way around and negate the char instead
> to silence the warnings.
> 
> Fixes: d2aa37411b8e ("x86/olpc/xo1/sci: Produce wakeup events for buttons and switches")
> Cc: stable@...r.kernel.org # 3.5+
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Reported-by: kernel test robot <lkp@...el.com>
> Reviewed-and-tested-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>

Applied, thanks!

> ---
>  arch/x86/platform/olpc/olpc-xo1-sci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/platform/olpc/olpc-xo1-sci.c b/arch/x86/platform/olpc/olpc-xo1-sci.c
> index f03a6883dcc6..89f25af4b3c3 100644
> --- a/arch/x86/platform/olpc/olpc-xo1-sci.c
> +++ b/arch/x86/platform/olpc/olpc-xo1-sci.c
> @@ -80,7 +80,7 @@ static void send_ebook_state(void)
>  		return;
>  	}
>  
> -	if (!!test_bit(SW_TABLET_MODE, ebook_switch_idev->sw) == state)
> +	if (test_bit(SW_TABLET_MODE, ebook_switch_idev->sw) == !!state)
>  		return; /* Nothing new to report. */
>  
>  	input_report_switch(ebook_switch_idev, SW_TABLET_MODE, state);
> -- 
> 2.36.1