tty: of_serial: add support for the DesignWare 8250

Support the DesignWare 8250 by a new compatible string and registering
the DesignWare helpers.  If the registration of the helpers fails, then
continue as a normal 8250 as we may still get some useful debug out.

Cc: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/devicetree/bindings/tty/serial/of-serial.txt

@@ -3,6 +3,7 @@
 Required properties:
 - compatible : one of:
 	- "ns8250"
+	- "ns8250dw"
 	- "ns16450"
 	- "ns16550a"
 	- "ns16550"

drivers/tty/serial/of_serial.c

@@ -78,6 +78,12 @@ static int __devinit of_platform_serial_setup(struct platform_device *ofdev,
 		}
 	}
 
+	if (of_device_is_compatible(np, "ns8250dw")) {
+		ret = serial8250_use_designware_io(port);
+		if (ret)
+			dev_warn(&ofdev->dev, "unable to register DesignWare 8250 helpers, continuing as a normal 8250\n");
+	}
+
 	port->type = type;
 	port->uartclk = clk;
 	port->flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP
@@ -176,6 +182,7 @@ static int of_platform_serial_remove(struct platform_device *ofdev)
  */
 static struct of_device_id __devinitdata of_platform_serial_table[] = {
 	{ .compatible = "ns8250",   .data = (void *)PORT_8250, },
+	{ .compatible = "ns8250dw", .data = (void *)PORT_8250, },
 	{ .compatible = "ns16450",  .data = (void *)PORT_16450, },
 	{ .compatible = "ns16550a", .data = (void *)PORT_16550A, },
 	{ .compatible = "ns16550",  .data = (void *)PORT_16550, },