hwmon: (w83l768ng) Fix fan speed control range

commit 33a7ab91 upstream.

The W83L786NG stores the fan speed on 4 bits while the sysfs interface
uses a 0-255 range. Thus the driver should scale the user input down
to map it to the device range, and scale up the value read from the
device before presenting it to the user. The reserved register nibble
should be left unchanged.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/hwmon/w83l786ng.c

@@ -447,8 +447,11 @@ store_pwm(struct device *dev, struct device_attribute *attr,
 	struct w83l786ng_data *data = i2c_get_clientdata(client);
 	u32 val = SENSORS_LIMIT(simple_strtoul(buf, NULL, 10), 0, 255);
 
+	val = DIV_ROUND_CLOSEST(val, 0x11);
+
 	mutex_lock(&data->update_lock);
-	data->pwm[nr] = val;
+	data->pwm[nr] = val * 0x11;
+	val |= w83l786ng_read_value(client, W83L786NG_REG_PWM[nr]) & 0xf0;
 	w83l786ng_write_value(client, W83L786NG_REG_PWM[nr], val);
 	mutex_unlock(&data->update_lock);
 	return count;
@@ -741,8 +744,9 @@ static struct w83l786ng_data *w83l786ng_update_device(struct device *dev)
 			    ? 0 : 1;
 			data->pwm_enable[i] =
 			    ((pwmcfg >> W83L786NG_PWM_ENABLE_SHIFT[i]) & 3) + 1;
-			data->pwm[i] = w83l786ng_read_value(client,
-			    W83L786NG_REG_PWM[i]);
+			data->pwm[i] =
+			    (w83l786ng_read_value(client, W83L786NG_REG_PWM[i])
+			     & 0x0f) * 0x11;
 		}