linux-kernel - Re: [PATCH 2/2] PWM: atmel: correct CDTY calculation

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Message-ID: <53231811.1020309@atmel.com>
Date:	Fri, 14 Mar 2014 15:54:09 +0100
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Thierry Reding <thierry.reding@...il.com>
CC:	<linux-kernel@...r.kernel.org>, Bo Shen <voice.shen@...el.com>,
	<linux-pwm@...r.kernel.org>
Subject: Re: [PATCH 2/2] PWM: atmel: correct CDTY calculation

On 14/03/2014 15:19, Alexandre Belloni :
>>>From the datasheet, the actual duty cycle is:
> (period - (1/clk) * CDTY)/period
> 
> This actually correct the polarity of the PWM and solves the issue that pwm-leds
> exhibits: when setting a duty cycle of 0 and then disabling a channel, the level
> was wrong (1 when the polarity was normal and 0 when the polarity was inversed).
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>

Acked-by: Nicolas Ferre <nicolas.ferre@...el.com>

> ---
>  drivers/pwm/pwm-atmel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index 2d69e9c431dd..0adc952cc4ef 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -133,7 +133,7 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  	prd = div;
>  	div *= duty_ns;
>  	do_div(div, period_ns);
> -	dty = div;
> +	dty = prd - div;
>  
>  	ret = clk_enable(atmel_pwm->clk);
>  	if (ret) {
> 


-- 
Nicolas Ferre
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