tb_switch_alloc
tb->root_switch = tb_switch_alloc(tb, &tb->dev, 0);
sw = tb_switch_alloc(tb, &parent_sw->dev, route);
sw = tb_switch_alloc(port->sw->tb, &port->sw->dev,
tb->root_switch = tb_switch_alloc(tb, &tb->dev, 0);
struct tb_switch *tb_switch_alloc(struct tb *tb, struct device *parent,