Merge branch 'core/xen' into x86/xen

1 files changed, 12 insertions, 4 deletions

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 342e12fb1c25..9ccc563d8730 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1908,15 +1908,23 @@ static int serial8250_startup(struct uart_port *port)
                  * kick the UART on a regular basis.
                  */
                 if (!(iir1 & UART_IIR_NO_INT) && (iir & UART_IIR_NO_INT)) {
+                        up->bugs |= UART_BUG_THRE;
                         pr_debug("ttyS%d - using backup timer\n", port->line);
-                        up->timer.function = serial8250_backup_timeout;
-                        up->timer.data = (unsigned long)up;
-                        mod_timer(&up->timer, jiffies +
-                                poll_timeout(up->port.timeout) + HZ / 5);
                 }
         }
 
         /*
+         * The above check will only give an accurate result the first time
+         * the port is opened so this value needs to be preserved.
+         */
+        if (up->bugs & UART_BUG_THRE) {
+                up->timer.function = serial8250_backup_timeout;
+                up->timer.data = (unsigned long)up;
+                mod_timer(&up->timer, jiffies +
+                          poll_timeout(up->port.timeout) + HZ / 5);
+        }
+
+        /*
          * If the "interrupt" for this port doesn't correspond with any
          * hardware interrupt, we use a timer-based system.  The original
          * driver used to do this with IRQ0.