linux-kernel - Re: [PATCH 1/2] PWM: atmel: Fix polarity handling

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Message-ID: <532317B8.7030302@atmel.com>
Date:	Fri, 14 Mar 2014 15:52:40 +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 1/2] PWM: atmel: Fix polarity handling

On 14/03/2014 15:19, Alexandre Belloni :
> When atmel_pwm_config() calculates and then sets the prescaler, it is
> overwriting the channel's CMR register so we are losing the CPOL configuration.
> 
> As atmel_pwm_config() is always called before enabling a channel, inverting the
> polarity doesn't work.
> 
> Fix that by reading CMR first and only overwriting the prescaler bits.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>

Indeed:

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

> ---
>  drivers/pwm/pwm-atmel.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index bf4144a14661..2d69e9c431dd 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -32,6 +32,7 @@
>  /* Bit field in CMR */
>  #define PWM_CMR_CPOL		(1 << 9)
>  #define PWM_CMR_UPD_CDTY	(1 << 10)
> +#define PWM_CMR_CPRE_MSK	0xF
>  
>  /* The following registers for PWM v1 */
>  #define PWMV1_CDTY		0x04
> @@ -104,6 +105,7 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  	unsigned long clk_rate, prd, dty;
>  	unsigned long long div;
>  	unsigned int pres = 0;
> +	u32 val;
>  	int ret;
>  
>  	if (test_bit(PWMF_ENABLED, &pwm->flags) && (period_ns != pwm->period)) {
> @@ -139,7 +141,10 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  		return ret;
>  	}
>  
> -	atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, pres);
> +	/* It is necessary to preserve CPOL, inside CMR */
> +	val = atmel_pwm_ch_readl(atmel_pwm, pwm->hwpwm, PWM_CMR);
> +	val = (val & ~PWM_CMR_CPRE_MSK) | (pres & PWM_CMR_CPRE_MSK);
> +	atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, val);
>  	atmel_pwm->config(chip, pwm, dty, prd);
>  
>  	clk_disable(atmel_pwm->clk);
> 


-- 
Nicolas Ferre
--
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