soundwire: bus: fix device number leak on errors

If the programming of the dev_number fails due to an IO error, a new
device_number will be assigned, resulting in a leak.

Make sure we only assign a device_number once per Slave device.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200113225637.17313-1-pierre-louis.bossart@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/bus.c

@@ -456,9 +456,11 @@ static int sdw_get_device_num(struct sdw_slave *slave)
 static int sdw_assign_device_num(struct sdw_slave *slave)
 {
 	int ret, dev_num;
+	bool new_device = false;
 
 	/* check first if device number is assigned, if so reuse that */
 	if (!slave->dev_num) {
+		if (!slave->dev_num_sticky) {
 			mutex_lock(&slave->bus->bus_lock);
 			dev_num = sdw_get_device_num(slave);
 			mutex_unlock(&slave->bus->bus_lock);
@@ -467,15 +469,22 @@ static int sdw_assign_device_num(struct sdw_slave *slave)
 					dev_num);
 				return dev_num;
 			}
+			slave->dev_num = dev_num;
+			slave->dev_num_sticky = dev_num;
+			new_device = true;
 		} else {
+			slave->dev_num = slave->dev_num_sticky;
+		}
+	}
+
+	if (!new_device)
 		dev_info(slave->bus->dev,
-			 "Slave already registered dev_num:%d\n",
+			 "Slave already registered, reusing dev_num:%d\n",
 			 slave->dev_num);
 
 	/* Clear the slave->dev_num to transfer message on device 0 */
 	dev_num = slave->dev_num;
 	slave->dev_num = 0;
-	}
 
 	ret = sdw_write(slave, SDW_SCP_DEVNUMBER, dev_num);
 	if (ret < 0) {
@@ -485,7 +494,7 @@ static int sdw_assign_device_num(struct sdw_slave *slave)
 	}
 
 	/* After xfer of msg, restore dev_num */
-	slave->dev_num = dev_num;
+	slave->dev_num = slave->dev_num_sticky;
 
 	return 0;
 }

include/linux/soundwire/sdw.h

@@ -546,7 +546,8 @@ struct sdw_slave_ops {
  * @debugfs: Slave debugfs
  * @node: node for bus list
  * @port_ready: Port ready completion flag for each Slave port
- * @dev_num: Device Number assigned by Bus
+ * @dev_num: Current Device Number, values can be 0 or dev_num_sticky
+ * @dev_num_sticky: one-time static Device Number assigned by Bus
  * @probed: boolean tracking driver state
  * @probe_complete: completion utility to control potential races
  * on startup between driver probe/initialization and SoundWire
@@ -575,6 +576,7 @@ struct sdw_slave {
 	struct list_head node;
 	struct completion *port_ready;
 	u16 dev_num;
+	u16 dev_num_sticky;
 	bool probed;
 	struct completion probe_complete;
 	struct completion enumeration_complete;