diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index f469869..69e072b 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -348,6 +348,11 @@
  *	do carrier detect and the dtr_rts method if it supports software
  *	management of these lines. Note that the dtr/rts raise is done each
  *	iteration as a hangup may have previously dropped them while we wait.
+ *
+ *	Caller holds tty lock.
+ *
+ *      NB: May drop and reacquire tty lock when blocking, so tty and tty_port
+ *      may have changed state (eg., may have been hung up).
  */
 
 int tty_port_block_til_ready(struct tty_port *port,