greybus: connection: make connection enable/disable thread safe

Add connection mutex to protect connection enabling and disabling.

This is needed to eventually allow drivers to manage the state of their
connections during operation (i.e. post probe and pre disconnect).
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/connection.c

@@ -170,6 +170,7 @@ gb_connection_create(struct gb_host_device *hd, int hd_cport_id,
 	connection->state = GB_CONNECTION_STATE_DISABLED;
 
 	atomic_set(&connection->op_cycle, 0);
+	mutex_init(&connection->mutex);
 	spin_lock_init(&connection->lock);
 	INIT_LIST_HEAD(&connection->operations);
 
@@ -390,9 +391,14 @@ int gb_connection_enable(struct gb_connection *connection,
 {
 	int ret;
 
+	mutex_lock(&connection->mutex);
+
+	if (connection->state == GB_CONNECTION_STATE_ENABLED)
+		goto out_unlock;
+
 	ret = gb_connection_hd_cport_enable(connection);
 	if (ret)
-		return ret;
+		goto err_unlock;
 
 	ret = gb_connection_svc_connection_create(connection);
 	if (ret)
@@ -407,6 +413,9 @@ int gb_connection_enable(struct gb_connection *connection,
 	if (ret)
 		goto err_svc_destroy;
 
+out_unlock:
+	mutex_unlock(&connection->mutex);
+
 	return 0;
 
 err_svc_destroy:
@@ -418,6 +427,8 @@ int gb_connection_enable(struct gb_connection *connection,
 	gb_connection_svc_connection_destroy(connection);
 err_hd_cport_disable:
 	gb_connection_hd_cport_disable(connection);
+err_unlock:
+	mutex_unlock(&connection->mutex);
 
 	return ret;
 }
@@ -425,8 +436,10 @@ EXPORT_SYMBOL_GPL(gb_connection_enable);
 
 void gb_connection_disable(struct gb_connection *connection)
 {
+	mutex_lock(&connection->mutex);
+
 	if (connection->state == GB_CONNECTION_STATE_DISABLED)
-		return;
+		goto out_unlock;
 
 	gb_connection_control_disconnected(connection);
 
@@ -437,6 +450,9 @@ void gb_connection_disable(struct gb_connection *connection)
 
 	gb_connection_svc_connection_destroy(connection);
 	gb_connection_hd_cport_disable(connection);
+
+out_unlock:
+	mutex_unlock(&connection->mutex);
 }
 EXPORT_SYMBOL_GPL(gb_connection_disable);
 

drivers/staging/greybus/connection.h

@@ -43,6 +43,7 @@ struct gb_connection {
 	u8				module_major;
 	u8				module_minor;
 
+	struct mutex			mutex;
 	spinlock_t			lock;
 	enum gb_connection_state	state;
 	struct list_head		operations;