linux-kernel - Re: [PATCH] pwm: rcar: Use div64_ul instead of do

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Message-ID: <20211117112559.jix3hmx7uwqmuryg@pengutronix.de>
Date:   Wed, 17 Nov 2021 12:25:59 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     cgel.zte@...il.com
Cc:     thierry.reding@...il.com, lee.jones@...aro.org,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Changcheng Deng <deng.changcheng@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] pwm: rcar: Use div64_ul instead of do_div

On Wed, Nov 17, 2021 at 02:08:54AM +0000, cgel.zte@...il.com wrote:
> From: Changcheng Deng <deng.changcheng@....com.cn>
> 
> do_div() does a 64-by-32 division. If the divisor is unsigned long, using
> div64_ul can avoid truncation to 32-bit.
> 
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Changcheng Deng <deng.changcheng@....com.cn>
> ---
>  drivers/pwm/pwm-rcar.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-rcar.c b/drivers/pwm/pwm-rcar.c
> index b437192380e2..fb475c188e1e 100644
> --- a/drivers/pwm/pwm-rcar.c
> +++ b/drivers/pwm/pwm-rcar.c
> @@ -111,7 +111,7 @@ static int rcar_pwm_set_counter(struct rcar_pwm_chip *rp, int div, int duty_ns,
>  	u32 cyc, ph;
>  
>  	one_cycle = (unsigned long long)NSEC_PER_SEC * 100ULL * (1 << div);
> -	do_div(one_cycle, clk_rate);
> +	div64_ul(one_cycle, clk_rate);

Same problem as with the atmel-hlcdc patch: The calling convention of
do_div and div64_ul are different and with the proposed patch the result
of the division is unused.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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