linux-kernel - Re: [PATCH] watchdog: davinci: Use div64_ul instead of do

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Date:   Wed, 24 Nov 2021 18:33:16 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     cgel.zte@...il.com
Cc:     wim@...ux-watchdog.org, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Changcheng Deng <deng.changcheng@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] watchdog: davinci: Use div64_ul instead of do_div

On Thu, Nov 25, 2021 at 01:49:24AM +0000, cgel.zte@...il.com wrote:
> From: Changcheng Deng <deng.changcheng@....com.cn>
> 
> 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.
> 
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Changcheng Deng <deng.changcheng@....com.cn>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
>  drivers/watchdog/davinci_wdt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/davinci_wdt.c b/drivers/watchdog/davinci_wdt.c
> index e6eaba6bae5b..584a56893b81 100644
> --- a/drivers/watchdog/davinci_wdt.c
> +++ b/drivers/watchdog/davinci_wdt.c
> @@ -134,7 +134,7 @@ static unsigned int davinci_wdt_get_timeleft(struct watchdog_device *wdd)
>  	timer_counter = ioread32(davinci_wdt->base + TIM12);
>  	timer_counter |= ((u64)ioread32(davinci_wdt->base + TIM34) << 32);
>  
> -	do_div(timer_counter, freq);
> +	timer_counter = div64_ul(timer_counter, freq);
>  
>  	return wdd->timeout - timer_counter;
>  }
> -- 
> 2.25.1
>