hwmon: (adm1031) Fix register overwrite in set_fan_div()

Don't rely on the register cache when setting a new fan clock divider.
For one thing, the cache might not have been initialized at all if the
driver has just been loaded. For another, the cached values may be old
and you never know what can happen in the driver's back.

Also invalidate the cache instead of trying to adjust the measured fan
speed: the whole point of changing the clock divider is to get a better
reading.
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Signed-off-by: NMark M. Hoffman <mhoffman@lightlink.com>

drivers/hwmon/adm1031.c

@@ -542,18 +542,26 @@ set_fan_div(struct device *dev, const char *buf, size_t count, int nr)
 		return -EINVAL;
 	
 	mutex_lock(&data->update_lock);
+	/* Get fresh readings */
+	data->fan_div[nr] = adm1031_read_value(client,
+					       ADM1031_REG_FAN_DIV(nr));
+	data->fan_min[nr] = adm1031_read_value(client,
+					       ADM1031_REG_FAN_MIN(nr));
+
+	/* Write the new clock divider and fan min */
 	old_div = FAN_DIV_FROM_REG(data->fan_div[nr]);
 	data->fan_div[nr] = (tmp & 0xC0) | (0x3f & data->fan_div[nr]);
 	new_min = data->fan_min[nr] * old_div / 
 		FAN_DIV_FROM_REG(data->fan_div[nr]);
 	data->fan_min[nr] = new_min > 0xff ? 0xff : new_min;
-	data->fan[nr] = data->fan[nr] * old_div / 
-		FAN_DIV_FROM_REG(data->fan_div[nr]);
 
 	adm1031_write_value(client, ADM1031_REG_FAN_DIV(nr), 
 			    data->fan_div[nr]);
 	adm1031_write_value(client, ADM1031_REG_FAN_MIN(nr), 
 			    data->fan_min[nr]);
+
+	/* Invalidate the cache: fan speed is no longer valid */
+	data->valid = 0;
 	mutex_unlock(&data->update_lock);
 	return count;
 }