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Message-Id: <20080303231332.a960132c.akpm@linux-foundation.org>
Date: Mon, 3 Mar 2008 23:13:32 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Alan Cox <alan@...rguk.ukuu.org.uk>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uart_get_baud_rate: stop mangling termios
On Wed, 20 Feb 2008 20:44:06 +0000 Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> 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;
drivers/serial/serial_core.c: In function 'uart_get_baud_rate':
drivers/serial/serial_core.c:340: warning: 'hung_up' may be used uninitialized in this function
It isn't completely obvious that this is a falsie.
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