thunderbolt: Run tb_xdp_handle_request() in system workqueue

We run all XDomain requests during discovery in tb->wq and since it only
runs one work at the time it means that sending back reply to the other
domain may be delayed too much depending whether there is an active
XDomain discovery request running.

To make sure we can send reply to the other domain as soon as possible
run tb_xdp_handle_request() in system workqueue instead. Since the
device can be hot-removed in the middle we need to make sure the domain
structure is still around when the function is run so increase reference
count before we schedule the reply work.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/tb.h

@@ -492,6 +492,13 @@ int tb_domain_approve_xdomain_paths(struct tb *tb, struct tb_xdomain *xd);
 int tb_domain_disconnect_xdomain_paths(struct tb *tb, struct tb_xdomain *xd);
 int tb_domain_disconnect_all_paths(struct tb *tb);
 
+static inline struct tb *tb_domain_get(struct tb *tb)
+{
+	if (tb)
+		get_device(&tb->dev);
+	return tb;
+}
+
 static inline void tb_domain_put(struct tb *tb)
 {
 	put_device(&tb->dev);

drivers/thunderbolt/xdomain.c

@@ -524,6 +524,8 @@ static void tb_xdp_handle_request(struct work_struct *work)
 out:
 	kfree(xw->pkg);
 	kfree(xw);
+
+	tb_domain_put(tb);
 }
 
 static bool
@@ -542,9 +544,9 @@ tb_xdp_schedule_request(struct tb *tb, const struct tb_xdp_header *hdr,
 		kfree(xw);
 		return false;
 	}
-	xw->tb = tb;
+	xw->tb = tb_domain_get(tb);
 
-	queue_work(tb->wq, &xw->work);
+	schedule_work(&xw->work);
 	return true;
 }