[PATCH v4 5/5] gpio: mvebu: improve handling of pwm zero on/off values

[Uwe Kleine-König]

Hello Baruch,

On Sun, Jan 17, 2021 at 03:17:06PM +0200, Baruch Siach wrote:
> Hardware appears to treat zero value as 2^32. Take advantage of this
> fact to support on/off values of up to UINT_MAX+1 == 2^32. Adjust both
> .apply and .get_sate to handle zero as a special case.

s/get_sate/get_state/

> Rounded up division result in .get_state can't be zero, since the
> dividend is now larger than 0. Remove check for this case.
> 
> Reported-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
> Analyzed-by: Russell King <linux at armlinux.org.uk>
> Signed-off-by: Baruch Siach <baruch at tkos.co.il>
> ---
>  drivers/gpio/gpio-mvebu.c | 38 ++++++++++++++++++++++----------------
>  1 file changed, 22 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
> index 6b017854ce61..37f5bd65062f 100644
> --- a/drivers/gpio/gpio-mvebu.c
> +++ b/drivers/gpio/gpio-mvebu.c
> @@ -667,22 +667,20 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
>  	spin_lock_irqsave(&mvpwm->lock, flags);
>  
>  	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_on_duration(mvpwm), &u);
> -	val = (unsigned long long) u * NSEC_PER_SEC;
> -	val = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);
> -	if (val)
> -		state->duty_cycle = val;
> +	/* Hardware treats zero as 2^32. See mvebu_pwm_apply(). */
> +	if (u > 0)
> +		val = (unsigned long long) u * NSEC_PER_SEC;
>  	else
> -		state->duty_cycle = 1;
> +		val = ((unsigned long long) UINT_MAX+1) * NSEC_PER_SEC;
> +	state->duty_cycle = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);

Instead of

	if (u > 0)
		val = (unsigned long long) u * NSEC_PER_SEC;
	else
		val = ((unsigned long long) UINT_MAX+1) * NSEC_PER_SEC;

	state->duty_cycle = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);

you could also write

	if (u > 0)
		val = u;
	else
		val = UINT_MAX + 1;

	state->duty_cycle = DIV_ROUND_UP_ULL(val * NSEC_PER_SEC, mvpwm->clk_rate);

which is a bit lighter (IMHO).

>  
> -	val = (unsigned long long) u; /* on duration */
>  	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
> -	val += (unsigned long long) u; /* period = on + off duration */
> -	val *= NSEC_PER_SEC;
> -	val = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);
> -	if (val)
> -		state->period = val;
> +	/* period = on + off duration */
> +	if (u > 0)
> +		val += (unsigned long long) u * NSEC_PER_SEC;
>  	else
> -		state->period = 1;
> +		val += ((unsigned long long) UINT_MAX+1) * NSEC_PER_SEC;
> +	state->period = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);

>  
>  	regmap_read(mvchip->regs, GPIO_BLINK_EN_OFF + mvchip->offset, &u);
>  	if (u)
> @@ -704,9 +702,15 @@ static int mvebu_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  
>  	val = (unsigned long long) mvpwm->clk_rate * state->duty_cycle;
>  	do_div(val, NSEC_PER_SEC);
> -	if (val > UINT_MAX)
> +	if (val > (unsigned long long) UINT_MAX+1)

Please add whitespace around the +

Best regards
Uwe

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