hvc_console: Change an mb() to smp_mb() and add some comments

I remember some history on this barrier.  There was a race between
open via /dev/console and the tty being fully setup.  Its also why
there is a temporary variable and the global is assigned at the end
of the function.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index 5a8a4c28c867fb67dd811afc0e728b2b2edf9cbc..f2685b747fb9f065e1ed08b71a6f9af6aec1ecbf 100644 (file)
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -876,8 +876,11 @@ static int hvc_init(void)
                goto stop_thread;
        }
 
-       /* FIXME: This mb() seems completely random.  Remove it. */
-       mb();
+       /*
+        * Make sure tty is fully registered before allowing it to be
+        * found by hvc_console_device.
+        */
+       smp_mb();
        hvc_driver = drv;
        return 0;