serial-core: restore termios settings when resume console ports

The commit 4547be7 rewrites suspend and resume functions. According
to this rewrite, when a serial port is a printk console device and
can suspend(without set no_console_suspend flag), it will definitely
call set_termios function during its resume, but parameter termios
isn't initialized, this will pass an unpredictable config to the
serial port. If this serial port is not a userspace opened tty device
, a suspend and resume action will make this serial port unusable.
I.E. ttyS0 is a printk console device, ttyS1 or keyboard+display is
userspace tty device, a suspend/resume action will make ttyS0
unusable.

If a serial port is both a printk console device and an opened tty
device, this issue can be overcome because it will call set_termios
again with the correct parameter in the uart_change_speed function.

Refer to the deleted content of commit 4547be7, revert parts relate
to restore settings into parameter termios. It is safe because if
a serial port is a printk console only device, the only meaningful
field in termios is c_cflag and its old config is saved in
uport->cons->cflag, if this port is also an opened tty device,
it will clear uport->cons->cflag in the uart_open and the old config
is saved in tty->termios.

Signed-off-by: Jason Wang <jason77.wang@gmail.com>
Acked-by: Stanislav Brabec <sbrabec@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 12 insertions, 0 deletions

diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index ff21200f94f4..bc6cddd10294 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -2066,6 +2066,18 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport)
          * Re-enable the console device after suspending.
          */
         if (console_suspend_enabled && uart_console(uport)) {
+                /*
+                 * First try to use the console cflag setting.
+                 */
+                memset(&termios, 0, sizeof(struct ktermios));
+                termios.c_cflag = uport->cons->cflag;
+
+                /*
+                 * If that's unset, use the tty termios setting.
+                 */
+                if (port->tty && port->tty->termios && termios.c_cflag == 0)
+                        termios = *(port->tty->termios);
+
                 uart_change_pm(state, 0);
                 uport->ops->set_termios(uport, &termios, NULL);
                 console_start(uport->cons);