serial: altera_jtaguart: add earlycon support

Nios2 currently uses its own early printk implementation, rather than
using unified earlycon support to show boot messages on altera_jtaguart
(and altera_uart for that matter).

Add earlycon support to altera_jtaguart so that other archs may use it. Also,
this will allow the early printk implementation in arch/nios2 to eventually be
removed in a future patch.

Cc: Ley Foon Tan <lftan@altera.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -1343,6 +1343,7 @@ config SERIAL_ALTERA_JTAGUART_CONSOLE
 	bool "Altera JTAG UART console support"
 	depends on SERIAL_ALTERA_JTAGUART=y
 	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
 	help
 	  Enable a Altera JTAG UART port to be the system console.
 

drivers/tty/serial/altera_jtaguart.c

@@ -383,6 +383,26 @@ console_initcall(altera_jtaguart_console_init);
 
 #define	ALTERA_JTAGUART_CONSOLE	(&altera_jtaguart_console)
 
+static void altera_jtaguart_earlycon_write(struct console *co, const char *s,
+					   unsigned int count)
+{
+	struct earlycon_device *dev = co->data;
+
+	uart_console_write(&dev->port, s, count, altera_jtaguart_console_putc);
+}
+
+static int __init altera_jtaguart_earlycon_setup(struct earlycon_device *dev,
+						 const char *options)
+{
+	if (!dev->port.membase)
+		return -ENODEV;
+
+	dev->con->write = altera_jtaguart_earlycon_write;
+	return 0;
+}
+
+OF_EARLYCON_DECLARE(juart, "altr,juart-1.0", altera_jtaguart_earlycon_setup);
+
 #else
 
 #define	ALTERA_JTAGUART_CONSOLE	NULL