linux-kernel - Re: [PATCH v9 04/11] pwm: clps711x: Use 64-bit division macro

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Date:   Tue, 17 Mar 2020 23:22:06 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Guru Das Srinagesh <gurus@...eaurora.org>
Cc:     Linux PWM List <linux-pwm@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König <uwe@...ine-koenig.org>,
        Subbaraman Narayanamurthy <subbaram@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexander Shiyan <shc_work@...l.ru>
Subject: Re: [PATCH v9 04/11] pwm: clps711x: Use 64-bit division macro

On Tue, Mar 17, 2020 at 9:05 PM Guru Das Srinagesh <gurus@...eaurora.org> wrote:
>
> Since the PWM framework is switching struct pwm_args.period's datatype
> to u64, prepare for this transition by using DIV64_U64_ROUND_CLOSEST to
> handle a 64-bit divisor.
>
> Cc: Alexander Shiyan <shc_work@...l.ru>
> Cc: Arnd Bergmann <arnd@...db.de>
>
> Signed-off-by: Guru Das Srinagesh <gurus@...eaurora.org>
> ---
>  drivers/pwm/pwm-clps711x.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c
> index 924d39a..ba9500a 100644
> --- a/drivers/pwm/pwm-clps711x.c
> +++ b/drivers/pwm/pwm-clps711x.c
> @@ -43,7 +43,7 @@ static void clps711x_pwm_update_val(struct clps711x_chip *priv, u32 n, u32 v)
>  static unsigned int clps711x_get_duty(struct pwm_device *pwm, unsigned int v)
>  {
>         /* Duty cycle 0..15 max */
> -       return DIV_ROUND_CLOSEST(v * 0xf, pwm->args.period);
> +       return DIV64_U64_ROUND_CLOSEST(v * 0xf, pwm->args.period);
>  }

Is it actually going to exceed U32_MAX? If not, a type cast may be
more appropriate here than the expensive 64-bit division.

       Arnd