mxser: keep only !tty test in ISR

The others are superfluous with tty refcounting in place now. And they
are racy in fact:
* tty_port_initialized() reports false for a small moment after
  interrupts are enabled.
* closing is 1 while the port is still alive.

The queues are flushed later during close anyway. So there is no need
for this special handling. Actually, the ISR should not flush the
queues. It should behave as every other driver, just queue the chars
into tty buffer and go on. But this will be changed later. There is
still a lot code depending on having tty in ISR (and not only tty_port).

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20211118073125.12283-4-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/mxser.c

@@ -262,7 +262,6 @@ struct mxser_port {
 	unsigned int xmit_head;
 	unsigned int xmit_tail;
 	unsigned int xmit_cnt;
-	int closing;
 
 	spinlock_t slock;
 };
@@ -903,7 +902,6 @@ static void mxser_close(struct tty_struct *tty, struct file *filp)
 		return;
 	if (tty_port_close_start(port, tty, filp) == 0)
 		return;
-	info->closing = 1;
 	mutex_lock(&port->mutex);
 	mxser_stop_rx(info);
 	mxser_flush_buffer(tty);
@@ -912,7 +910,6 @@ static void mxser_close(struct tty_struct *tty, struct file *filp)
 	mxser_shutdown_port(port);
 	tty_port_set_initialized(port, 0);
 	mutex_unlock(&port->mutex);
-	info->closing = 0;
 	/* Right now the tty_port set is done outside of the close_end helper
 	   as we don't yet have everyone using refcounts */	
 	tty_port_close_end(port, tty);
@@ -1668,7 +1665,7 @@ static bool mxser_port_isr(struct mxser_port *port)
 
 	iir &= MOXA_MUST_IIR_MASK;
 	tty = tty_port_tty_get(&port->port);
-	if (!tty || port->closing || !tty_port_initialized(&port->port)) {
+	if (!tty) {
 		status = inb(port->ioaddr + UART_LSR);
 		outb(port->FCR | UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT,
 				port->ioaddr + UART_FCR);