Re: [PATCH v11 06/12] pwm: imx27: Use 64-bit division macro and function

[Arnd Bergmann]

On Fri, Mar 20, 2020 at 2:42 AM Guru Das Srinagesh <gurus@xxxxxxxxxxxxxx> wrote:

> @@ -240,8 +240,7 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>
>         period_cycles /= prescale;
>         c = (unsigned long long)period_cycles * state->duty_cycle;
> -       do_div(c, state->period);
> -       duty_cycles = c;
> +       duty_cycles = div64_u64(c, state->period);
>

This change looks fine, but I wonder if the code directly above it

        c = clk_get_rate(imx->clk_per);
        c *= state->period;
        do_div(c, 1000000000);
        period_cycles = c;

might run into an overflow when both the clock rate and the period
are large numbers.

      Arnd