linux-kernel - Re: [PATCH 6/7] pwm: jz4740: Make PWM start with the active part

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Date:   Fri, 9 Aug 2019 19:10:58 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Thierry Reding <thierry.reding@...il.com>, od@...c.me,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] pwm: jz4740: Make PWM start with the active part

On Fri, Aug 09, 2019 at 02:30:30PM +0200, Paul Cercueil wrote:
> The PWM will always start with the inactive part. To counter that,
> when PWM is enabled we switch the configured polarity, and use
> 'period - duty + 1' as the real duty.

Where does the + 1 come from? This looks wrong. (So if duty=0 is
requested you use duty = period + 1?)

> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/pwm/pwm-jz4740.c | 22 +++++++++++++---------
>  1 file changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
> index 85e2110aae4f..8df898429d47 100644
> --- a/drivers/pwm/pwm-jz4740.c
> +++ b/drivers/pwm/pwm-jz4740.c
> @@ -121,6 +121,7 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  		   *parent_clk = clk_get_parent(clk);
>  	unsigned long rate, parent_rate, period, duty;
>  	unsigned long long tmp;
> +	bool polarity_inversed;
>  	int ret;
>  
>  	parent_rate = clk_get_rate(parent_clk);
> @@ -183,24 +184,27 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	/* Reset counter to 0 */
>  	regmap_write(jz4740->map, TCU_REG_TCNTc(pwm->hwpwm), 0);
>  
> -	/* Set duty */
> -	regmap_write(jz4740->map, TCU_REG_TDHRc(pwm->hwpwm), duty);
> -
>  	/* Set period */
>  	regmap_write(jz4740->map, TCU_REG_TDFRc(pwm->hwpwm), period);
>  
> +	/*
> +	 * The PWM will always start with the inactive part. To counter that,
> +	 * when PWM is enabled we switch the configured polarity, and use
> +	 * 'period - duty + 1' as the real duty.
> +	 */
> +
> +	/* Set duty */
> +	regmap_write(jz4740->map, TCU_REG_TDHRc(pwm->hwpwm), period - duty + 1);
> +

Before you set duty first, then period, now you do it the other way
round. Is there a good reason?

>  	/* Set polarity */
> -	switch (state->polarity) {
> -	case PWM_POLARITY_NORMAL:
> +	polarity_inversed = state->polarity == PWM_POLARITY_INVERSED;
> +	if (!polarity_inversed ^ state->enabled)

Why does state->enabled suddenly matter here?

>  		regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),
>  				   TCU_TCSR_PWM_INITL_HIGH, 0);
> -		break;
> -	case PWM_POLARITY_INVERSED:
> +	else
>  		regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),
>  				   TCU_TCSR_PWM_INITL_HIGH,
>  				   TCU_TCSR_PWM_INITL_HIGH);
> -		break;
> -	}
>  
>  	if (state->enabled)
>  		jz4740_pwm_enable(chip, pwm);

Best regards
Uwe

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