--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -433,6 +433,13 @@ serial_out(struct uart_8250_port *up, in
 	default:
 		outb(value, up->port.iobase + offset);
 	}
+
+#if defined(CONFIG_IDT_EB434) || defined(CONFIG_MIKROTIK_RB500)
+	__SLOW_DOWN_IO;
+	__SLOW_DOWN_IO;
+	__SLOW_DOWN_IO;
+	__SLOW_DOWN_IO;
+#endif
 }
 
 static void
