workaround serial hang with SMP enabled

SVN-Revision: 22557

target/linux/cns3xxx/patches-2.6.31/210-cns3xxx_smp_serial_fix.patch

@@ -0,0 +1,39 @@
+--- a/drivers/serial/8250.c
++++ b/drivers/serial/8250.c
+@@ -1743,6 +1743,7 @@ static void serial8250_backup_timeout(un
+ 	unsigned int iir, ier = 0, lsr;
+ 	unsigned long flags;
+ 
++	spin_lock_irqsave(&up->port.lock, flags);
+ 	/*
+ 	 * Must disable interrupts or else we risk racing with the interrupt
+ 	 * based handler.
+@@ -1760,10 +1761,8 @@ static void serial8250_backup_timeout(un
+ 	 * the "Diva" UART used on the management processor on many HP
+ 	 * ia64 and parisc boxes.
+ 	 */
+-	spin_lock_irqsave(&up->port.lock, flags);
+ 	lsr = serial_in(up, UART_LSR);
+ 	up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
+-	spin_unlock_irqrestore(&up->port.lock, flags);
+ 	if ((iir & UART_IIR_NO_INT) && (up->ier & UART_IER_THRI) &&
+ 	    (!uart_circ_empty(&up->port.info->xmit) || up->port.x_char) &&
+ 	    (lsr & UART_LSR_THRE)) {
+@@ -1771,12 +1770,14 @@ static void serial8250_backup_timeout(un
+ 		iir |= UART_IIR_THRI;
+ 	}
+ 
+-	if (!(iir & UART_IIR_NO_INT))
+-		serial8250_handle_port(up);
+-
+ 	if (is_real_interrupt(up->port.irq))
+ 		serial_out(up, UART_IER, ier);
+ 
++	spin_unlock_irqrestore(&up->port.lock, flags);
++
++	if (!(iir & UART_IIR_NO_INT))
++		serial8250_handle_port(up);
++
+ 	/* Standard timer interval plus 0.2s to keep the port running */
+ 	mod_timer(&up->timer,
+ 		jiffies + poll_timeout(up->port.timeout) + HZ / 5);