linux-kernel - [PATCH] uart_get_baud_rate: stop mangling termios

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Message-ID: <20080220204406.1d5f74bc@core>
Date:	Wed, 20 Feb 2008 20:44:06 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: [PATCH] uart_get_baud_rate: stop mangling termios

Russell King noticed this one: We have to avoid replacing B0 when we pick
a baud rate for a "hung up" port. Ugly but the proper fix is in the tty
layer and means changing the tty<->serial interfaces so we will defer
that for now.

Signed-off-by: Alan Cox <alan@...hat.com>

diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.25-rc2-mm1/drivers/serial/serial_core.c linux-2.6.25-rc2-mm1/drivers/serial/serial_core.c
--- linux.vanilla-2.6.25-rc2-mm1/drivers/serial/serial_core.c	2008-02-19 11:03:01.000000000 +0000
+++ linux-2.6.25-rc2-mm1/drivers/serial/serial_core.c	2008-02-20 16:22:49.000000000 +0000
@@ -329,13 +329,15 @@
  *	If it's still invalid, we try 9600 baud.
  *
  *	Update the @termios structure to reflect the baud rate
- *	we're actually going to be using.
+ *	we're actually going to be using. Don't do this for the case
+ *	where B0 is requested ("hang up").
  */
 unsigned int
 uart_get_baud_rate(struct uart_port *port, struct ktermios *termios,
 		   struct ktermios *old, unsigned int min, unsigned int max)
 {
 	unsigned int try, baud, altbaud = 38400;
+	int hung_up;
 	upf_t flags = port->flags & UPF_SPD_MASK;
 
 	if (flags == UPF_SPD_HI)
@@ -360,8 +362,10 @@
 		/*
 		 * Special case: B0 rate.
 		 */
-		if (baud == 0)
+		if (baud == 0) {
+			hung_up = 1;
 			baud = 9600;
+		}
 
 		if (baud >= min && baud <= max)
 			return baud;
@@ -373,7 +377,9 @@
 		termios->c_cflag &= ~CBAUD;
 		if (old) {
 			baud = tty_termios_baud_rate(old);
-			tty_termios_encode_baud_rate(termios, baud, baud);
+			if (!hung_up)
+				tty_termios_encode_baud_rate(termios,
+								baud, baud);
 			old = NULL;
 			continue;
 		}
@@ -382,7 +388,8 @@
 		 * As a last resort, if the quotient is zero,
 		 * default to 9600 bps
 		 */
-		tty_termios_encode_baud_rate(termios, 9600, 9600);
+		if (!hung_up)
+			tty_termios_encode_baud_rate(termios, 9600, 9600);
 	}
 
 	return 0;
--
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