[PATCH v2] fix serial console resume-from-suspend

[PATCH v2] fix serial console resume-from-suspend

[Peter Hurley]

Greg,

This v2 respin removes the dependency on the patch to which Alan objected
(regarding not hanging up remote serial console modems).

This patch fixes bugzilla #69751, where the serial console is garbled
after resume from suspend.

Although this was originally reported as a regression, this bug is
actually caused when a user-space process (such as setserial or stty)
opens and then closes the associated tty. The resultant tty port shutdown
caused the console termios settings to be lost, and thus uninitialized when
the console was subsequently suspended and then resumed (and there was not
an associated open tty).

This patch preserves the cflag settings from the associated tty as the
console cflags (which reflect the current line settings anyway). The
console cflags are already used to restore the console line settings if
there is not an associated open tty.

The side-effect of this patch is that the serial console line settings
are persistent. Originally, only the first-time initialization of the
associated port inherited the console line settings; now, each time the
associated port is initialized to the most recent line settings.

Peter Hurley (1):
  serial: core: Preserve termios c_cflag for console resume

 drivers/tty/serial/serial_core.c | 3 +++
 1 file changed, 3 insertions(+)

-- 
2.0.0

[PATCH v2] serial: core: Preserve termios c_cflag for console resume

[Peter Hurley]

When a tty is opened for the serial console, the termios c_cflag
settings are inherited from the console line settings.
However, if the tty is subsequently closed, the termios settings
are lost. This results in a garbled console if the console is later
suspended and resumed.

Preserve the termios c_cflag for the serial console when the tty
is shutdown; this reflects the most recent line settings.

Fixes: Bugzilla #69751, 'serial console does not wake from S3'
Reported-by: Valerio Vanni <valerio.vanni@inwind.it>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
 drivers/tty/serial/serial_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index b68550d..aab7190 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -239,6 +239,9 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
 		/*
 		 * Turn off DTR and RTS early.
 		 */
+		if (uart_console(uport) && tty)
+			uport->cons->cflag = tty->termios.c_cflag;
+
 		if (!tty || (tty->termios.c_cflag & HUPCL))
 			uart_clear_mctrl(uport, TIOCM_DTR | TIOCM_RTS);
 
-- 
2.0.0

Re: [PATCH v2] serial: core: Preserve termios c_cflag for console resume

[One Thousand Gnomes]

On Wed,  9 Jul 2014 09:21:14 -0400
Peter Hurley <peter@hurleysoftware.com> wrote:

> When a tty is opened for the serial console, the termios c_cflag
> settings are inherited from the console line settings.
> However, if the tty is subsequently closed, the termios settings
> are lost. This results in a garbled console if the console is later
> suspended and resumed.
> 
> Preserve the termios c_cflag for the serial console when the tty
> is shutdown; this reflects the most recent line settings.
> 
> Fixes: Bugzilla #69751, 'serial console does not wake from S3'
> Reported-by: Valerio Vanni <valerio.vanni@inwind.it>
> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>

Acked-by: Alan Cox <alan@linux.intel.com>