linux-kernel - Re: [PATCH 3/4] pwm: mxs: add support for inverse polarity

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Message-ID: <20190923082735.tzxyhvjlnztsxhsc@pengutronix.de>
Date:   Mon, 23 Sep 2019 10:27:35 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        devicetree@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/4] pwm: mxs: add support for inverse polarity

On Mon, Sep 23, 2019 at 10:13:47AM +0200, Rasmus Villemoes wrote:
> If I'm reading of_pwm_xlate_with_flags() right, existing device trees
> that set #pwm-cells = 2 will continue to work.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  drivers/pwm/pwm-mxs.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-mxs.c b/drivers/pwm/pwm-mxs.c
> index 284107784dad..c46697acaf11 100644
> --- a/drivers/pwm/pwm-mxs.c
> +++ b/drivers/pwm/pwm-mxs.c
> @@ -25,8 +25,11 @@
>  #define  PERIOD_PERIOD(p)	((p) & 0xffff)
>  #define  PERIOD_PERIOD_MAX	0x10000
>  #define  PERIOD_ACTIVE_HIGH	(3 << 16)
> +#define  PERIOD_ACTIVE_LOW	(2 << 16)
> +#define  PERIOD_INACTIVE_HIGH	(3 << 18)
>  #define  PERIOD_INACTIVE_LOW	(2 << 18)
>  #define  PERIOD_POLARITY_NORMAL	(PERIOD_ACTIVE_HIGH | PERIOD_INACTIVE_LOW)
> +#define  PERIOD_POLARITY_INVERSE	(PERIOD_ACTIVE_LOW | PERIOD_INACTIVE_HIGH)
>  #define  PERIOD_CDIV(div)	(((div) & 0x7) << 20)
>  #define  PERIOD_CDIV_MAX	8
>  
> @@ -50,9 +53,7 @@ static int mxs_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	unsigned int period_cycles, duty_cycles;
>  	unsigned long rate;
>  	unsigned long long c;
> -
> -	if (state->polarity != PWM_POLARITY_NORMAL)
> -		return -ENOTSUPP;
> +	unsigned int pol_bits;
>  
>  	rate = clk_get_rate(mxs->clk);
>  	while (1) {
> @@ -81,9 +82,12 @@ static int mxs_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  			return ret;
>  	}
>  
> +	pol_bits = state->polarity == PWM_POLARITY_NORMAL ?
> +		PERIOD_POLARITY_NORMAL : PERIOD_POLARITY_INVERSE;
> +
>  	writel(duty_cycles << 16,
>  	       mxs->base + PWM_ACTIVE0 + pwm->hwpwm * 0x20);
> -	writel(PERIOD_PERIOD(period_cycles) | PERIOD_POLARITY_NORMAL | PERIOD_CDIV(div),
> +	writel(PERIOD_PERIOD(period_cycles) | pol_bits | PERIOD_CDIV(div),

When will this affect the output? Only on the next start of a period, or
immediatly? Can it happen that this results in a mixed output (i.e. a
period that has already the new duty cycle from the line above but not
the new polarity (or period)?

Best regards
Uwe

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