serial: 8250_early: optimize early 8250 uart

In early 8250, IER is already zero so no point in writing this - twice
per line

This helped improve the SystemC model based ARC OSCI platform

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Rob Herring <robh@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
index 4858b8a..ce2a8ab 100644 (file)
--- a/drivers/tty/serial/8250/8250_early.c
+++ b/drivers/tty/serial/8250/8250_early.c
@@ -95,13 +95,16 @@ static void __init early_serial8250_write(struct console *console,
 
        /* Save the IER and disable interrupts */
        ier = serial8250_early_in(port, UART_IER);
-       serial8250_early_out(port, UART_IER, 0);
+       if (ier)
+               serial8250_early_out(port, UART_IER, 0);
 
        uart_console_write(port, s, count, serial_putc);
 
        /* Wait for transmitter to become empty and restore the IER */
        wait_for_xmitr(port);
-       serial8250_early_out(port, UART_IER, ier);
+
+       if (ier)
+               serial8250_early_out(port, UART_IER, ier);
 }
 
 static unsigned int __init probe_baud(struct uart_port *port)