Char: moxa, fix and optimise empty timer

patch c4342205 in mainline.

moxa, fix and optimise empty timer

don't wait and delete empty timer in empty timer function. Also fire next
empty timer at rounded jiffies to save power.

This fixes a lockup, because we wait for ourselves to finish forever.
(i.e.  sync called from the timer itself).
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/char/moxa.c

@@ -1040,14 +1040,14 @@ static void check_xmit_empty(unsigned long data)
 	struct moxa_port *ch;
 
 	ch = (struct moxa_port *) data;
-	del_timer_sync(&moxa_ports[ch->port].emptyTimer);
 	if (ch->tty && (ch->statusflags & EMPTYWAIT)) {
 		if (MoxaPortTxQueue(ch->port) == 0) {
 			ch->statusflags &= ~EMPTYWAIT;
 			tty_wakeup(ch->tty);
 			return;
 		}
-		mod_timer(&moxa_ports[ch->port].emptyTimer, jiffies + HZ);
+		mod_timer(&moxa_ports[ch->port].emptyTimer,
+				round_jiffies(jiffies + HZ));
 	} else
 		ch->statusflags &= ~EMPTYWAIT;
 }