linux-kernel - Re: pwm: atmel: Fix disabling of PWM channels

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Date:	Fri, 10 Jun 2016 10:29:34 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Guillermo Rodriguez <guille.rodriguez@...il.com>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>
Subject: Re: pwm: atmel: Fix disabling of PWM channels

Hi,

On 13/05/2016 at 13:09:37 +0200, Guillermo Rodriguez wrote :
> When disabling a PWM channel, the PWM clock was being stopped
> immediately after writing to PWM_DIS. As a result, the disabling
> of the PWM channel did not complete properly, and the PWM output
> might be left at the wrong level.
> 
> Fix this by waiting for the channel to be effectively disabled
> (by checking the PWM_SR register) before disabling the clock.
> 
> Signed-off-by: Guillermo Rodriguez <guille.rodriguez@...il.com>
> ---
>  drivers/pwm/pwm-atmel.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index 0e4bd4e..a714434 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -271,6 +271,16 @@ static void atmel_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>  	mutex_unlock(&atmel_pwm->isr_lock);
>  	atmel_pwm_writel(atmel_pwm, PWM_DIS, 1 << pwm->hwpwm);
>  
> +	/*
> +	 * Wait for the PWM channel disable operation to be effective before
> +	 * stopping the clock.
> +	 */
> +	timeout = jiffies + 2 * HZ;
> +	while ((atmel_pwm_readl(atmel_pwm, PWM_SR)& (1 << pwm->hwpwm)) &&
> +	       time_before(jiffies, timeout)) {
> +		usleep_range(10, 100);
> +	}
> +

While this seems good, can you tell on which SoC you observed that? I'd
like to understand whether this is only on v1 or v2 or both.

Thanks!

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com