tty: serial: bcm63xx: Enable DT earlycon support

This enables early console output if there is a chosen/stdout-path
property referencing a UART node with the "brcm,bcm6345-uart" compatible
string.  The bootloader sets up the pinmux and baud/parity/etc.
Tested on bcm3384 (MIPS, DT).

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/bcm63xx_uart.c b/drivers/tty/serial/bcm63xx_uart.c
index b615af2..109dea7 100644
--- a/drivers/tty/serial/bcm63xx_uart.c
+++ b/drivers/tty/serial/bcm63xx_uart.c
@@ -782,6 +782,26 @@
 
 console_initcall(bcm63xx_console_init);
 
+static void bcm_early_write(struct console *con, const char *s, unsigned n)
+{
+	struct earlycon_device *dev = con->data;
+
+	uart_console_write(&dev->port, s, n, bcm_console_putchar);
+	wait_for_xmitr(&dev->port);
+}
+
+static int __init bcm_early_console_setup(struct earlycon_device *device,
+					  const char *opt)
+{
+	if (!device->port.membase)
+		return -ENODEV;
+
+	device->con->write = bcm_early_write;
+	return 0;
+}
+
+OF_EARLYCON_DECLARE(bcm63xx_uart, "brcm,bcm6345-uart", bcm_early_console_setup);
+
 #define BCM63XX_CONSOLE	(&bcm63xx_console)
 #else
 #define BCM63XX_CONSOLE	NULL