mailbox: skip complete wait event if timer expired

BugLink: http://bugs.launchpad.net/bugs/1710646

commit cc6eeaa3 upstream.

If a wait_for_completion_timeout() call returns due to a timeout,
complete() can get called after returning from the wait which is
incorrect and can cause subsequent transmissions on a channel to fail.
Since the wait_for_completion_timeout() sees the completion variable
is non-zero caused by the erroneous/spurious complete() call, and
it immediately returns without waiting for the time as expected by the
client.

This patch fixes the issue by skipping complete() call for the timer
expiry.

Fixes: 2b6d83e2 ("mailbox: Introduce framework for mailbox")
Reported-by: Alexey Klimov <alexey.klimov@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/mailbox/mailbox.c

@@ -108,7 +108,7 @@ static void tx_tick(struct mbox_chan *chan, int r)
 	if (mssg && chan->cl->tx_done)
 		chan->cl->tx_done(chan->cl, mssg, r);
 
-	if (chan->cl->tx_block)
+	if (r != -ETIME && chan->cl->tx_block)
 		complete(&chan->tx_complete);
 }
 
@@ -272,8 +272,8 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg)
 
 		ret = wait_for_completion_timeout(&chan->tx_complete, wait);
 		if (ret == 0) {
-			t = -EIO;
-			tx_tick(chan, -EIO);
+			t = -ETIME;
+			tx_tick(chan, t);
 		}
 	}