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

Guenter Roeck
2015-02-06T18:28:48Z

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.

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
>