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Subject[RFC, 2.6.26.2-rc1] 8250: fix break handling for Intel 82571
From 7500b1f602aad75901774a67a687ee985d85893f Mon Sep 17 00:00:00 2001
From: Aristeu Rozanski <arozansk@redhat.com>
Date: Wed, 23 Jul 2008 21:29:45 -0700
Subject: [PATCH] 8250: fix break handling for Intel 82571

[ Upstream commit 7500b1f602aad75901774a67a687ee985d85893f ]

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>
CC: Oliver Pinter <oliver.pntr@gmail.com>

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 27f34a9..a97f1ae 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)



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