xhci: dbctty: disable ECHO flag by default

commit 2b857d6 upstream.

When /dev/ttyDBC0 device is created then by default ECHO flag
is set for the terminal device. However if data arrives from
a peer before application using /dev/ttyDBC0 applies its set
of terminal flags then the arriving data will be echoed which
might not be desired behavior.

Fixes: 4521f16 ("xhci: dbctty: split dbc tty driver registration and unregistration functions.")
Cc: stable <stable@kernel.org>
Signed-off-by: Łukasz Bartosik <ukaszb@chromium.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/stable/20250610111802.18742-1-ukaszb%40chromium.org
Link: https://lore.kernel.org/r/20250627144127.3889714-4-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Łukasz Bartosik

drivers/usb/host/xhci-dbgtty.c

@@ -585,6 +585,7 @@ int dbc_tty_init(void)
 	dbc_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
 	dbc_tty_driver->subtype = SERIAL_TYPE_NORMAL;
 	dbc_tty_driver->init_termios = tty_std_termios;
+	dbc_tty_driver->init_termios.c_lflag &= ~ECHO;
 	dbc_tty_driver->init_termios.c_cflag =
 			B9600 | CS8 | CREAD | HUPCL | CLOCAL;
 	dbc_tty_driver->init_termios.c_ispeed = 9600;