Re: [PATCH] staging: pi433: using div64_u64() instead of do_div()

[Christophe JAILLET]

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@xxxxxxxxxxxxxx/