linux-kernel - Re: [PATCH -next v2] ethernet: renesas: Use div64_ul instead of do

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Message-ID: <CAMuHMdXL4nfiq8B-PtAiQmCQkZMBP8t-CUBO4bbMZumiA=QpaQ@mail.gmail.com>
Date:   Thu, 18 Nov 2021 09:39:42 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Yang Li <yang.lee@...ux.alibaba.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next v2] ethernet: renesas: Use div64_ul instead of do_div

Hi Yang,

On Thu, Nov 18, 2021 at 4:13 AM Yang Li <yang.lee@...ux.alibaba.com> 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/renesas/ravb_main.c:2492:1-7: 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>

Thanks for your patch!

> --- 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);
>
>         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",

Please also replace

    #include <asm/div64.h>

by

#include <linux/math64.h>

With that added:

Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds