[PATCH] Perle multimodem card (PCI-RAS) detection

Get the Perle quad-modem PCI card (PCI-RAS4) detected by serial driver.  It
may also get the PCI-RAS8 running, but can't guarantee as I didn't had one for
testing.

Signed-off-by: Thomas Hoehn <thomas.hoehn@avocent.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/serial/8250.c

@@ -920,12 +920,16 @@ static void autoconfig(struct uart_8250_port *up, unsigned int probeflags)
 #ifdef __i386__
 		outb(0xff, 0x080);
 #endif
-		scratch2 = serial_inp(up, UART_IER);
+		/*
+		 * Mask out IER[7:4] bits for test as some UARTs (e.g. TL
+		 * 16C754B) allow only to modify them if an EFR bit is set.
+		 */
+		scratch2 = serial_inp(up, UART_IER) & 0x0f;
 		serial_outp(up, UART_IER, 0x0F);
 #ifdef __i386__
 		outb(0, 0x080);
 #endif
-		scratch3 = serial_inp(up, UART_IER);
+		scratch3 = serial_inp(up, UART_IER) & 0x0f;
 		serial_outp(up, UART_IER, scratch);
 		if (scratch2 != 0 || scratch3 != 0x0F) {
 			/*