[PATCH v2 1/3] serial: 8250_early: optimize early 8250 uart

[Vineet Gupta <Vineet.Gupta1@synopsys.com>]

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

This helped improve the SystemC model based ARC OSCI platform

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
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>
---
 drivers/tty/serial/8250/8250_early.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
index 4858b8a99d3b..ce2a8abd1f54 100644
--- 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)
-- 
1.9.1