linux-kernel - Re: [PATCH v3 6/8] hwmon: pwm-fan: Extract __set_pwm() function to only modify PWM duty cycle

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Date:	Fri, 6 Feb 2015 10:27:25 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Lukasz Majewski <l.majewski@...sung.com>
Cc:	Eduardo Valentin <edubezval@...il.com>,
	Kamil Debski <k.debski@...sung.com>,
	Jean Delvare <jdelvare@...e.de>, Kukjin Kim <kgene@...nel.org>,
	lm-sensors@...sensors.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>, devicetree@...r.kernel.org,
	Lukasz Majewski <l.majewski@...ess.pl>,
	Kukjin Kim <kgene.kim@...sung.com>,
	linux-kernel@...r.kernel.org,
	Sjoerd Simons <sjoerd.simons@...labora.co.uk>,
	Abhilash Kesavan <kesavan.abhilash@...il.com>,
	Abhilash Kesavan <a.kesavan@...sung.com>
Subject: Re: [PATCH v3 6/8] hwmon: pwm-fan: Extract __set_pwm() function to
 only modify PWM duty cycle

On Fri, Feb 06, 2015 at 05:59:06PM +0100, Lukasz Majewski wrote:
> It was necessary to decouple code handling writing to sysfs from the one
> responsible for setting PWM of the fan.
> Due to that, new __set_pwm() method was extracted, which is responsible for
> only setting new PWM duty cycle.
> 
> Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
> ---
> Changes for v2:
> - None
> Changes for v3:
> - The commit headline has been reedited.
> ---
>  drivers/hwmon/pwm-fan.c | 35 ++++++++++++++++++++++-------------
>  1 file changed, 22 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 1991d903..870e100 100644
> --- a/drivers/hwmon/pwm-fan.c
> +++ b/drivers/hwmon/pwm-fan.c
> @@ -33,21 +33,15 @@ struct pwm_fan_ctx {
>  	unsigned char pwm_value;
>  };
>  
> -static ssize_t set_pwm(struct device *dev, struct device_attribute *attr,
> -		       const char *buf, size_t count)
> +static int  __set_pwm(struct pwm_fan_ctx *ctx, unsigned long pwm)
>  {
> -	struct pwm_fan_ctx *ctx = dev_get_drvdata(dev);
> -	unsigned long pwm, duty;
> -	ssize_t ret;
> -
> -	if (kstrtoul(buf, 10, &pwm) || pwm > MAX_PWM)
> -		return -EINVAL;
> -
> -	mutex_lock(&ctx->lock);
> +	unsigned long duty;
> +	int ret;
>  
>  	if (ctx->pwm_value == pwm)
> -		goto exit_set_pwm_no_change;
> +		return 0;
>  
Why did you move this check outside the lock ? With this change there 
is no guarantee that pwm_value wasn't changed while waiting for the lock.

Guenter

> +	mutex_lock(&ctx->lock);
>  	if (pwm == 0) {
>  		pwm_disable(ctx->pwm);
>  		goto exit_set_pwm;
> @@ -66,13 +60,28 @@ static ssize_t set_pwm(struct device *dev, struct device_attribute *attr,
>  
>  exit_set_pwm:
>  	ctx->pwm_value = pwm;
> -exit_set_pwm_no_change:
> -	ret = count;
>  exit_set_pwm_err:
>  	mutex_unlock(&ctx->lock);
>  	return ret;
>  }
>  
> +static ssize_t set_pwm(struct device *dev, struct device_attribute *attr,
> +		       const char *buf, size_t count)
> +{
> +	struct pwm_fan_ctx *ctx = dev_get_drvdata(dev);
> +	unsigned long pwm;
> +	int ret;
> +
> +	if (kstrtoul(buf, 10, &pwm) || pwm > MAX_PWM)
> +		return -EINVAL;
> +
> +	ret = __set_pwm(ctx, pwm);
> +	if (ret)
> +		return ret;
> +
> +	return count;
> +}
> +
>  static ssize_t show_pwm(struct device *dev,
>  			struct device_attribute *attr, char *buf)
>  {
> -- 
> 2.0.0.rc2
> 
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