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

Lukasz Majewski
2015-02-08T20:52:43Z

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On Fri, 6 Feb 2015 10:27:25 -0800
Guenter Roeck <linux@roeck-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@samsung.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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