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>

drivers/tty/serial/Kconfig

@@ -1297,6 +1297,7 @@ config SERIAL_BCM63XX_CONSOLE
 	bool "Console on BCM63xx serial port"
 	depends on SERIAL_BCM63XX=y
 	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
 	help
 	  If you have enabled the serial port on the BCM63xx CPU
 	  you can make it the console by answering Y to this option.

drivers/tty/serial/bcm63xx_uart.c

@@ -782,6 +782,26 @@ static int __init bcm63xx_console_init(void)
 
 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