Subject: [PATCH] PWM: atmel-pwm: use request/free instead of enable/disable

From: [email-masked] (Bo Shen)
Date: Sun, 29 Sep 2013 18:12:05 +0800

Hi Alexandre,

On 9/28/2013 04:10, Alexandre Belloni wrote:
> I found that disabling a pwm while it is at a low level will actually put it
> back at a high level. The main symptom is that leds-pwm is calling pwm_disable()
> after setting the duty cycle to 0. Hence, instead of getting a switched off LED,
> you get an LED lit up at full brightness.
>
> Solve that by using the request and free callbacks to enable and disable the
> pwm channels and the clock.
>
> Signed-off-by: Alexandre Belloni <[email-masked]>
> ---
>
> This patch applies after:
>    [PATCH v4] PWM: atmel-pwm: add PWM controller driver
>
>   drivers/pwm/pwm-atmel.c | 14 +++++---------
>   1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index 6af7a50..4526e71 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -209,7 +209,7 @@ static int atmel_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
>   	return 0;
>   }
>
> -static int atmel_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> +static int atmel_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
>   {
>   	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
>   	int ret;
> @@ -225,23 +225,19 @@ static int atmel_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
>   	return 0;
>   }
>
> -static void atmel_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> +static void atmel_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
>   {
>   	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
> -	u32 val;
>
>   	atmel_pwm_writel(atmel_pwm, PWM_DIS, 1 << pwm->hwpwm);
> -
> -	val = atmel_pwm_readl(atmel_pwm, PWM_SR);
> -	if ((val & PWM_SR_ALL_CH_ON) == 0)
> -		clk_disable(atmel_pwm->clk);
> +	clk_disable(atmel_pwm->clk);
>   }
>
>   static const struct pwm_ops atmel_pwm_ops = {
>   	.config = atmel_pwm_config,
>   	.set_polarity = atmel_pwm_set_polarity,
> -	.enable = atmel_pwm_enable,
> -	.disable = atmel_pwm_disable,
> +	.request = atmel_pwm_request,
> +	.free = atmel_pwm_free,

This will cause pwmadd_chip failure.

Code from <drivers/pwm/core.c>, in function: pwmadd_chip()
---8>---
if (!chip || !chip->dev || !chip->ops || !chip->ops->config ||
     !chip->ops->enable || !chip->ops->disable)
     return -EINVAL;
---<8---

>   	.owner = THIS_MODULE,
>   };

Best Regards,
Bo Shen