serial: doc: .(un)throttle() are serialized by the tty layer

Document that .(un)throttle() are serialized with each other, and with
termios modification by the tty layer.

Reported-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/Documentation/serial/driver b/Documentation/serial/driver
index 03b703cf9318..7fb80682e394 100644
--- a/Documentation/serial/driver
+++ b/Documentation/serial/driver
@@ -137,7 +137,8 @@ hardware.
         should be sent to the serial port.
         This will be called only if hardware assisted flow control is enabled.
 
-        Locking: none.
+        Locking: serialized with .unthrottle() and termios modification by the
+                 tty layer.
 
   unthrottle(port)
         Notify the serial driver that characters can now be sent to the serial
@@ -145,7 +146,8 @@ hardware.
         disciplines.
         This will be called only if hardware assisted flow control is enabled.
 
-        Locking: none.
+        Locking: serialized with .throttle() and termios modification by the
+                 tty layer.
 
   send_xchar(port,ch)
         Transmit a high priority character, even if the port is stopped.