linux-kernel - Re: [PATCH] scsi: use sector_div instead of do

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Date:	Tue, 24 Nov 2015 13:48:59 +0100
From:	Johannes Thumshirn <jthumshirn@...e.de>
To:	Arnd Bergmann <arnd@...db.de>, linux-scsi@...r.kernel.org
Cc:	jbottomley@...n.com, martin.petersen@...cle.com, nico@...xnic.net,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] scsi: use sector_div instead of do_div

On Fri, 2015-11-20 at 17:38 +0100, Arnd Bergmann wrote:
> do_div is the wrong way to divide a sector_t, as it is less
> efficient when sector_t is 32-bit wide. With the upcoming
> do_div optimizations, the kernel starts warning about this:
> 
> drivers/scsi/scsi_debug.c: In function 'dif_store':
> include/asm-generic/div64.h:207:28: warning: comparison of distinct
> pointer types lacks a cast
> 
> This changes the code to use sector_div instead, which always
> produces optimal code.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> Found on the ARM randconfig build today, after I merged Nico's
> patches
> for linux-next
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index dfcc45bb03b1..ec622ba9864a 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -678,7 +678,7 @@ static void *fake_store(unsigned long long lba)
>  
>  static struct sd_dif_tuple *dif_store(sector_t sector)
>  {
> -	sector = do_div(sector, sdebug_store_sectors);
> +	sector = sector_div(sector, sdebug_store_sectors);
>  
>  	return dif_storep + sector;
>  }
> @@ -2780,7 +2780,7 @@ static unsigned long lba_to_map_index(sector_t
> lba)
>  		lba += scsi_debug_unmap_granularity -
>  			scsi_debug_unmap_alignment;
>  	}
> -	do_div(lba, scsi_debug_unmap_granularity);
> +	sector_div(lba, scsi_debug_unmap_granularity);
>  
>  	return lba;
>  }
> 
> --
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Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>
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