serial: core: fix port-lock initialisation

Commit f743061a ("serial: core: Initialise spin lock before use in
uart_configure_port()") tried to work around a breakage introduced by
commit a3cb39d2 ("serial: core: Allow detach and attach serial
device for console") by adding a second initialisation of the port lock
when registering the port.

As reported by the build robots [1], this doesn't really solve the
regression introduced by the console-detach changes and also adds a
second redundant initialisation of the lock for normal ports.

Start cleaning up this mess by removing the redundant initialisation and
making sure that the port lock is again initialised once-only for ports
that aren't already in use as a console.

[1] https://lore.kernel.org/r/20200802054852.GR23458@shao2-debian

Fixes: f743061a ("serial: core: Initialise spin lock before use in uart_configure_port()")
Fixes: a3cb39d2 ("serial: core: Allow detach and attach serial device for console")
Cc: stable <stable@vger.kernel.org>     # 5.7
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200909143101.15389-2-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -2378,13 +2378,6 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
 		/* Power up port for set_mctrl() */
 		uart_change_pm(state, UART_PM_STATE_ON);
 
-		/*
-		 * If this driver supports console, and it hasn't been
-		 * successfully registered yet, initialise spin lock for it.
-		 */
-		if (port->cons && !(port->cons->flags & CON_ENABLED))
-			__uart_port_spin_lock_init(port);
-
 		/*
 		 * Ensure that the modem control lines are de-activated.
 		 * keep the DTR setting that is set in uart_set_options()
@@ -2900,7 +2893,12 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 		goto out;
 	}
 
-	uart_port_spin_lock_init(uport);
+	/*
+	 * If this port is in use as a console then the spinlock is already
+	 * initialised.
+	 */
+	if (!uart_console_enabled(uport))
+		__uart_port_spin_lock_init(uport);
 
 	if (uport->cons && uport->dev)
 		of_console_check(uport->dev->of_node, uport->cons->name, uport->line);