linux-kernel - Re: [PATCH v7 08/13] pwm: sifive: Use 64-bit division macros for period and duty cycle

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Date:   Thu, 26 Mar 2020 09:37:43 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     gurus@...eaurora.org
CC:     linux-pwm@...r.kernel.org, thierry.reding@...il.com,
        uwe@...ine-koenig.org, subbaram@...eaurora.org,
        linux-kernel@...r.kernel.org, gurus@...eaurora.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org, yash.shah@...ive.com,
        Atish Patra <Atish.Patra@....com>
Subject:     Re: [PATCH v7 08/13] pwm: sifive: Use 64-bit division macros for period and duty cycle

On Mon, 09 Mar 2020 12:35:11 PDT (-0700), gurus@...eaurora.org wrote:
> Because period and duty cycle are defined in the PWM framework structs
> as ints with units of nanoseconds, the maximum time duration that can be
> set is limited to ~2.147 seconds. Redefining them as u64 values will
> enable larger time durations to be set.
>
> As a first step, prepare drivers to handle the switch to u64 period and
> duty_cycle by replacing division operations involving pwm period and duty cycle
> with their 64-bit equivalents as appropriate. The actual switch to u64 period
> and duty_cycle follows as a separate patch.
>
> Where the dividend is 64-bit but the divisor is 32-bit, use *_ULL
> macros:
> - DIV_ROUND_UP_ULL
> - DIV_ROUND_CLOSEST_ULL
> - div_u64
>
> Where the divisor is 64-bit (dividend may be 32-bit or 64-bit), use
> DIV64_* macros:
> - DIV64_U64_ROUND_CLOSEST
> - div64_u64
>
> Cc: Palmer Dabbelt <palmer@...belt.com>
> Cc: Paul Walmsley <paul.walmsley@...ive.com>
> Cc: linux-riscv@...ts.infradead.org
> Cc: Yash Shah <yash.shah@...ive.com>
> Cc: Atish Patra <atish.patra@....com>
>
> Signed-off-by: Guru Das Srinagesh <gurus@...eaurora.org>
> ---
>  drivers/pwm/pwm-sifive.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> index cc63f9b..62de0bb 100644
> --- a/drivers/pwm/pwm-sifive.c
> +++ b/drivers/pwm/pwm-sifive.c
> @@ -181,7 +181,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	 * consecutively
>  	 */
>  	num = (u64)duty_cycle * (1U << PWM_SIFIVE_CMPWIDTH);
> -	frac = DIV_ROUND_CLOSEST_ULL(num, state->period);
> +	frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
>  	/* The hardware cannot generate a 100% duty cycle */
>  	frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);

Acked-by: Palmer Dabbelt <palmerdabbelt@...gle.com>