[cns3xxx]: workaround serial hang with SMP enabled

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@22557 3c298f89-4303-0410-b956-a3cf2f4a3e73

diff --git a/target/linux/cns3xxx/patches-2.6.31/210-cns3xxx_smp_serial_fix.patch b/target/linux/cns3xxx/patches-2.6.31/210-cns3xxx_smp_serial_fix.patch
new file mode 100644 (file)
index 0000000..a9b45ae
--- /dev/null
+++ b/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);