tty: of_serial: add no-loopback-test property

The loopback test mode is not implemented in all
NS16550 compatible UARTs. The 8250 driver uses the
UPF_SKIP_TEST flag to indicate this, however it is
not possible to set this flag via device-tree.

Add a new 'no-loopback-test' property, and modify
the of_serial driver to set the UPF_SKIP_TEST flag
if the property is present.
Signed-off-by: NGabor Juhos <juhosg@openwrt.org>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -25,6 +25,8 @@ Optional properties:
   accesses to the UART (e.g. TI davinci).
 - used-by-rtas : set to indicate that the port is in use by the OpenFirmware
   RTAS and should not be registered.
+- no-loopback-test: set to indicate that the port does not implements loopback
+  test mode
 
 Example:
 

drivers/tty/serial/of_serial.c

@@ -105,6 +105,10 @@ static int __devinit of_platform_serial_setup(struct platform_device *ofdev,
 	port->uartclk = clk;
 	port->flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP
 		| UPF_FIXED_PORT | UPF_FIXED_TYPE;
+
+	if (of_find_property(np, "no-loopback-test", NULL))
+		port->flags |= UPF_SKIP_TEST;
+
 	port->dev = &ofdev->dev;
 
 	if (type == PORT_TEGRA)