serial: 8250: Do XR17V35X specific wakeup in serial8250_do_startup

The XR17V35X UART needs the ECB bit set in its XR_EFR
register to enable access to IER [7:5], ISR [5:4], FCR[5:4],
MCR[7:5], and MSR [7:0].

Also reset the IER register to mask interrupts after access
to all bits of this register has been enabled.

This makes my 8-port XR17V35X working with the in-kernel
serial driver.

Cc: Joe Schultz <jschultz@xes-inc.com>
Signed-off-by: NJoerg Roedel <jroedel@suse.de>
Reviewed-by: NPeter Hurley <peter@hurleysoftware.com>
Reviewed-by: NMichael Welling <mwelling@ieee.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_port.c

@@ -1834,6 +1834,21 @@ int serial8250_do_startup(struct uart_port *port)
 	 */
 	enable_rsa(up);
 #endif
+
+	if (port->type == PORT_XR17V35X) {
+		/*
+		 * First enable access to IER [7:5], ISR [5:4], FCR [5:4],
+		 * MCR [7:5] and MSR [7:0]
+		 */
+		serial_port_out(port, UART_XR_EFR, UART_EFR_ECB);
+
+		/*
+		 * Make sure all interrups are masked until initialization is
+		 * complete and the FIFOs are cleared
+		 */
+		serial_port_out(port, UART_IER, 0);
+	}
+
 	/*
 	 * Clear the FIFO buffers and disable them.
 	 * (they will be reenabled in set_termios())