netdev - Re: [PATCH -next] ethernet: renesas: Use div64_ul instead of do

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Message-ID: <6851a10a-e7cf-b533-ab9d-0df539bbba00@omp.ru>
Date:   Thu, 18 Nov 2021 12:07:45 +0300
From:   Sergey Shtylyov <s.shtylyov@....ru>
To:     Yang Li <yang.lee@...ux.alibaba.com>, <davem@...emloft.net>
CC:     <kuba@...nel.org>, <netdev@...r.kernel.org>,
        <linux-renesas-soc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] ethernet: renesas: Use div64_ul instead of do_div

Hello!

    Why you didn't Cc me (as a reviewer)?

On 18.11.2021 5:50, Yang Li wrote:

> do_div() does a 64-by-32 division. Here the divisor is an
> unsigned long which on some platforms is 64 bit wide. So use
> div64_ul instead of do_div to avoid a possible truncation.
> 
> Eliminate the following coccicheck warning:
> ./drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:2742:1-7: WARNING:
> do_div() does a 64-by-32 division, please consider using div64_ul
> instead.
> 
> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Signed-off-by: Yang Li <yang.lee@...ux.alibaba.com>
> ---
>   drivers/net/ethernet/renesas/ravb_main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index b4c597f..2b89710 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -2489,7 +2489,7 @@ static int ravb_set_gti(struct net_device *ndev)
>   		return -EINVAL;
>   
>   	inc = 1000000000ULL << 20;
> -	do_div(inc, rate);
> +	inc = div64_ul(inc, rate);

    Why not just:

	inc = div64_ul(1000000000ULL << 20, rate);

>   	if (inc < GTI_TIV_MIN || inc > GTI_TIV_MAX) {
>   		dev_err(dev, "gti.tiv increment 0x%llx is outside the range 0x%x - 0x%x\n",

MBR, Sergey