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

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

[Alexander Lobakin]

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@vger.kernel.org # 3.5+
Reported-by: Guenter Roeck <linux@roeck-us.net>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-and-tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
---
 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

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

[Yury Norov]

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@vger.kernel.org # 3.5+
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Reported-by: kernel test robot <lkp@intel.com>
> Reviewed-and-tested-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.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