hwmon: (gpio-fan) Fix set_rpm() return value

The set_rpm function is used as a 'store' callback of a device attribute,
and as such it should return with the number of bytes consumed. However
since commit 0d01110 ("hwmon: (gpio-fan) Add regulator support"),
the function returns with zero on success.

Due to this, the function gets called again and again whenever the user
tries to change the FAN speed by writing the desired RPM value into the
'fan1_target' sysfs attribute.

The broken behaviour can be reproduced easily. For example, the following
command never returns unless it gets terminated:

  $ echo 500 > /sys/class/hwmon/hwmon1/fan1_target
  ^C
  $

Change the code to return with the same value as the 'count' parameter
on success to indicate that all bytes from the input buffer are consumed.
The function behaved the same way prior to the offending change.

Cc: [email protected]
Fixes: 0d01110 ("hwmon: (gpio-fan) Add regulator support")
Signed-off-by: Gabor Juhos <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Guenter Roeck <[email protected]>

Author: juhosg

drivers/hwmon/gpio-fan.c

@@ -291,7 +291,7 @@ static ssize_t set_rpm(struct device *dev, struct device_attribute *attr,
 {
 	struct gpio_fan_data *fan_data = dev_get_drvdata(dev);
 	unsigned long rpm;
-	int ret = count;
+	int ret;
 
 	if (kstrtoul(buf, 10, &rpm))
 		return -EINVAL;
@@ -308,7 +308,7 @@ static ssize_t set_rpm(struct device *dev, struct device_attribute *attr,
 exit_unlock:
 	mutex_unlock(&fan_data->lock);
 
-	return ret;
+	return ret ? ret : count;
 }
 
 static DEVICE_ATTR_RW(pwm1);