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:	Sun, 8 Feb 2015 21:52:43 +0100
From:	Lukasz Majewski <l.majewski@...ess.pl>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Lukasz Majewski <l.majewski@...sung.com>,
	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,
	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, 6 Feb 2015 10:27:25 -0800
Guenter Roeck <linux@...ck-us.net> wrote:

> 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.

Grrr. You are obviously right here. I will fix this. Thanks for spotting

Best regards,
Lukasz Majewski

> 
> 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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