linux-kernel - Re: [PATCH] staging: pi433: using div64_u64() instead of do

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Date:   Wed, 9 Feb 2022 20:15:13 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     David Laight <David.Laight@...LAB.COM>,
        'Jiapeng Chong' <jiapeng.chong@...ux.alibaba.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     "linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Abaci Robot <abaci@...ux.alibaba.com>
Subject: Re: [PATCH] staging: pi433: using div64_u64() instead of do_div()

Le 21/01/2022 à 14:34, David Laight a écrit :
> From: Jiapeng Chong
>> Sent: 21 January 2022 11:50
>> Subject: [PATCH] staging: pi433: using div64_u64() instead of do_div()
>>
>> Clean the following coccicheck warning:
>>
>> ./drivers/staging/pi433/rf69.c:286:1-7: WARNING: do_div() does a
>> 64-by-32 division, please consider using div64_u64 instead.
> 
> That is one of patchcheck's worse warnings.
> 
> You need to check the domain of the divisor, not its type.
> 
> do_div() exists to avoid expensive 64bit divides when the
> divisor is small.
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 
> 

Moreover, the patch is broken by itself.

See [1] were it was already reported that do_div() and div64_u64() don't 
have the same calling convention.

Looks that div64_u64() and div64_ul() works the same way.


CJ

[1]: 
https://lore.kernel.org/linux-kernel/20211117112559.jix3hmx7uwqmuryg@pengutronix.de/