linux-kernel - Re: [PATCH 4/9v2] usb: host: ehci.h: fix single statement macros

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Date:	Thu, 10 Dec 2015 14:40:39 -0300
From:	"Geyslan G. Bem" <geyslan@...il.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	Peter Senna Tschudin <peter.senna@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/9v2] usb: host: ehci.h: fix single statement macros

2015-12-10 14:26 GMT-03:00 Sergei Shtylyov <sergei.shtylyov@...entembedded.com>:
> On 12/10/2015 05:56 PM, Geyslan G. Bem wrote:
>
>>>>>>> Don't use the 'do {} while (0)' wrapper in a single statement macro.
>>>>>>>
>>>>>>> Caught by checkpatch: "WARNING: Single statement macros should not
>>>>>>> use a do {} while (0) loop"
>>>>>>>
>>>>>>> Signed-off-by: Geyslan G. Bem <geyslan@...il.com>
>>>>>>> ---
>>>>>>>     drivers/usb/host/ehci.h | 4 ++--
>>>>>>>     1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
>>>>>>> index cfeebd8..945000a 100644
>>>>>>> --- a/drivers/usb/host/ehci.h
>>>>>>> +++ b/drivers/usb/host/ehci.h
>>>>>>> @@ -244,9 +244,9 @@ struct ehci_hcd {                   /* one per
>>>>>>> controller */
>>>>>>>           /* irq statistics */
>>>>>>>     #ifdef EHCI_STATS
>>>>>>>           struct ehci_stats       stats;
>>>>>>> -#      define COUNT(x) do { (x)++; } while (0)
>>>>>>> +#      define COUNT(x) ((x)++)
>>>>>>>     #else
>>>>>>> -#      define COUNT(x) do {} while (0)
>>>>>>> +#      define COUNT(x) ((void) 0)
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>      Why not just empty #define?
>>>>>
>>>>>
>>>>>
>>>>> Indeed. I'll change it.
>>>>> Tks Sergei.
>>>>
>>>>
>>>>
>>>> Since COUNT is not used to return the empty #define is ok. Another way
>>>> is to use #define COUNT(x) (0) to get a 0 when necessary to read
>>>> returns.
>
>
>>>     Just 0, no parens please.
>
>
>> Ok, no parens, since there's no evaluation.
>
>
>    It's because the literals don't need parens at all.
>
>> Then my change is:
>>
>> -#      define COUNT(x) do { (x)++; } while (0)
>> +#      define COUNT(x) (++(x))
>>   #else
>> -#      define COUNT(x) do {} while (0)
>> +#      define COUNT(x) 0
>>
>> Pre-increment allowing to return the updated x.
>
>
>    Why if there was a post-increment before?
There's nothing wrong with post-increment. The pre one would be
necessary if using return.

>
>    Anyway, this talk is quite pointless since the macro didn't return any
> value anyway.
You're sure, there's no use anywhere of the return of that macro indeed.

Sending v2 soon.

>
> MBR, Sergei
>



-- 
Regards,

Geyslan G. Bem
hackingbits.com
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