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

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Message-ID: <20220210080603.GJ1951@kadam>
Date:   Thu, 10 Feb 2022 11:06:03 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     David Laight <David.Laight@...LAB.COM>,
        'Jiapeng Chong' <jiapeng.chong@...ux.alibaba.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "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()

On Wed, Feb 09, 2022 at 08:15:13PM +0100, Christophe JAILLET wrote:
> 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.

We could mark those as __must_check functions.

regards,
dan carpenter