mxser: don't start TX from tty_operations::put_char

TX is not supposed to be started from tty_operations::put_char. Line
disciplines ought to call tty_operations::put_char several times and
then do a single tty_operations::flush_chars to start TX.

Fix this in mxser by removing TX startup from mxser_put_char.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210618061516.662-58-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/mxser.c

@@ -998,17 +998,7 @@ static int mxser_put_char(struct tty_struct *tty, unsigned char ch)
 	info->xmit_head &= SERIAL_XMIT_SIZE - 1;
 	info->xmit_cnt++;
 	spin_unlock_irqrestore(&info->slock, flags);
-	if (!tty->flow.stopped) {
-		if (!tty->hw_stopped ||
-				(info->type == PORT_16550A) ||
-				info->board->must_hwid) {
-			spin_lock_irqsave(&info->slock, flags);
-			outb(info->IER & ~UART_IER_THRI, info->ioaddr + UART_IER);
-			info->IER |= UART_IER_THRI;
-			outb(info->IER, info->ioaddr + UART_IER);
-			spin_unlock_irqrestore(&info->slock, flags);
-		}
-	}
+
 	return 1;
 }