8250: fix break handling for Intel 82571

Intel 82571 has a "Serial Over LAN" feature that doesn't properly
implements the receiving of break characters.  When a break is received,
it doesn't set UART_LSR_DR and unless another character is received, the
break won't be received by the application.

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 27f34a9f9cb7..a97f1ae11f78 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1293,7 +1293,18 @@ receive_chars(struct uart_8250_port *up, unsigned int *status)
         char flag;
 
         do {
-                ch = serial_inp(up, UART_RX);
+                if (likely(lsr & UART_LSR_DR))
+                        ch = serial_inp(up, UART_RX);
+                else
+                        /*
+                         * Intel 82571 has a Serial Over Lan device that will
+                         * set UART_LSR_BI without setting UART_LSR_DR when
+                         * it receives a break. To avoid reading from the
+                         * receive buffer without UART_LSR_DR bit set, we
+                         * just force the read character to be 0
+                         */
+                        ch = 0;
+
                 flag = TTY_NORMAL;
                 up->port.icount.rx++;
 
@@ -1342,7 +1353,7 @@ receive_chars(struct uart_8250_port *up, unsigned int *status)
 
 ignore_char:
                 lsr = serial_inp(up, UART_LSR);
-        } while ((lsr & UART_LSR_DR) && (max_count-- > 0));
+        } while ((lsr & (UART_LSR_DR | UART_LSR_BI)) && (max_count-- > 0));
         spin_unlock(&up->port.lock);
         tty_flip_buffer_push(tty);
         spin_lock(&up->port.lock);
@@ -1425,7 +1436,7 @@ serial8250_handle_port(struct uart_8250_port *up)
 
         DEBUG_INTR("status = %x...", status);
 
-        if (status & UART_LSR_DR)
+        if (status & (UART_LSR_DR | UART_LSR_BI))
                 receive_chars(up, &status);
         check_modem_status(up);
         if (status & UART_LSR_THRE)