linux-kernel - Re: [PATCH 2/2] drivers: pwm: pwm-atmel: add support to allow run time changing of pwm parameters

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Date:   Thu, 23 Feb 2017 10:21:48 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Claudiu Beznea <claudiu.beznea@...rochip.com>
Cc:     thierry.reding@...il.com, robh+dt@...nel.org, pawel.moll@....com,
        mark.rutland@....com, ijc+devicetree@...lion.org.uk,
        galak@...eaurora.org, boris.brezillon@...e-electrons.com,
        linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] drivers: pwm: pwm-atmel: add support to allow run
 time changing of pwm parameters

On 23/02/2017 at 10:38:40 +0200, Claudiu Beznea wrote:
> sama5d2 supports changing of pwm parameters like period and
> duty factor without first to disable pwm. Since pwm code
> is supported by more than one SoC add allow_runtime_cfg
> parameter to atmel_pwm_chip data structure. This will be
> filled statically for every SoC, saved in pwm specific
> structure at probing time and checked while configuring
> the device. Based on this, pwm clock will not be
> enabled/disabled while configuring if it still enabled.
> 
> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
> ---
>  drivers/pwm/pwm-atmel.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index 4406639..9e1dece 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -68,6 +68,8 @@ struct atmel_pwm_chip {
>  
>  	void (*config)(struct pwm_chip *chip, struct pwm_device *pwm,
>  		       unsigned long dty, unsigned long prd);
> +
> +	bool allow_runtime_cfg;
>  };
>  
>  static inline struct atmel_pwm_chip *to_atmel_pwm_chip(struct pwm_chip *chip)
> @@ -114,7 +116,8 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  	u32 val;
>  	int ret;
>  
> -	if (pwm_is_enabled(pwm) && (period_ns != pwm_get_period(pwm))) {
> +	if (!atmel_pwm->allow_runtime_cfg &&
> +	    pwm_is_enabled(pwm) && (period_ns != pwm_get_period(pwm))) {
>  		dev_err(chip->dev, "cannot change PWM period while enabled\n");
>  		return -EBUSY;
>  	}
> @@ -139,10 +142,12 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  	do_div(div, period_ns);
>  	dty = prd - div;
>  
> -	ret = clk_enable(atmel_pwm->clk);
> -	if (ret) {
> -		dev_err(chip->dev, "failed to enable PWM clock\n");
> -		return ret;
> +	if (!pwm_is_enabled(pwm)) {
> +		ret = clk_enable(atmel_pwm->clk);
> +		if (ret) {
> +			dev_err(chip->dev, "failed to enable PWM clock\n");
> +			return ret;
> +		}
>  	}
>  

It is probably worth switching to atomic PWM instead of changing this
function. This would simplify the whole driver.

>  	/* It is necessary to preserve CPOL, inside CMR */
> @@ -155,7 +160,9 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  	atmel_pwm->updated_pwms &= ~(1 << pwm->hwpwm);
>  	mutex_unlock(&atmel_pwm->isr_lock);
>  
> -	clk_disable(atmel_pwm->clk);
> +	if (!pwm_is_enabled(pwm))
> +		clk_disable(atmel_pwm->clk);
> +
>  	return ret;
>  }
>  
> @@ -294,18 +301,22 @@ static const struct pwm_ops atmel_pwm_ops = {
>  struct atmel_pwm_data {
>  	void (*config)(struct pwm_chip *chip, struct pwm_device *pwm,
>  		       unsigned long dty, unsigned long prd);
> +	bool allow_runtime_cfg;
>  };
>  
>  static const struct atmel_pwm_data atmel_pwm_data_v1 = {
>  	.config = atmel_pwm_config_v1,
> +	.allow_runtime_cfg = false,

This is useless as it is false even if not explicitly set.

>  };
>  
>  static const struct atmel_pwm_data atmel_pwm_data_v2 = {
>  	.config = atmel_pwm_config_v2,
> +	.allow_runtime_cfg = false,

ditto.

>  };
>  
>  static const struct atmel_pwm_data atmel_pwm_data_v3 = {
>  	.config = atmel_pwm_config_v3,
> +	.allow_runtime_cfg = true,
>  };
>  
>  static const struct platform_device_id atmel_pwm_devtypes[] = {
> @@ -399,6 +410,7 @@ static int atmel_pwm_probe(struct platform_device *pdev)
>  	atmel_pwm->chip.npwm = 4;
>  	atmel_pwm->chip.can_sleep = true;
>  	atmel_pwm->config = data->config;
> +	atmel_pwm->allow_runtime_cfg = data->allow_runtime_cfg;

It is probably worth having a pointer to the atmel_pwm_data instead of
having to copy all the members.

>  	atmel_pwm->updated_pwms = 0;
>  	mutex_init(&atmel_pwm->isr_lock);
>  
> -- 
> 2.7.4
> 

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