nios2: add early printk support

Signed-off-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/kernel/prom.c

@@ -1,7 +1,7 @@
 /*
  * Device tree support
  *
- * Copyright (C) 2013 Altera Corporation
+ * Copyright (C) 2013, 2015 Altera Corporation
  * Copyright (C) 2010 Thomas Chou <thomas@wytron.com.tw>
  *
  * Based on MIPS support for CONFIG_OF device tree support
@@ -30,6 +30,7 @@
 #include <linux/of_fdt.h>
 #include <linux/io.h>
 
+#include <asm/prom.h>
 #include <asm/sections.h>
 
 void __init early_init_dt_add_memory_arch(u64 base, u64 size)
@@ -63,3 +64,52 @@ void __init early_init_devtree(void *params)
 
 	early_init_dt_scan(params);
 }
+
+#ifdef CONFIG_EARLY_PRINTK
+static int __init early_init_dt_scan_serial(unsigned long node,
+			const char *uname, int depth, void *data)
+{
+	u64 *addr64 = (u64 *) data;
+	const char *p;
+
+	/* only consider serial nodes */
+	if (strncmp(uname, "serial", 6) != 0)
+		return 0;
+
+	p = of_get_flat_dt_prop(node, "compatible", NULL);
+	if (!p)
+		return 0;
+
+	/*
+	 * We found an altera_jtaguart but it wasn't configured for console, so
+	 * skip it.
+	 */
+#ifndef CONFIG_SERIAL_ALTERA_JTAGUART_CONSOLE
+	if (strncmp(p, "altr,juart", 10) == 0)
+		return 0;
+#endif
+
+	/*
+	 * Same for altera_uart.
+	 */
+#ifndef CONFIG_SERIAL_ALTERA_UART_CONSOLE
+	if (strncmp(p, "altr,uart", 9) == 0)
+		return 0;
+#endif
+
+	*addr64 = fdt_translate_address((const void *)initial_boot_params,
+		node);
+
+	return *addr64 == OF_BAD_ADDR ? 0 : 1;
+}
+
+unsigned long __init of_early_console(void)
+{
+	u64 base = 0;
+
+	if (of_scan_flat_dt(early_init_dt_scan_serial, &base))
+		return (u32)ioremap(base, 32);
+	else
+		return 0;
+}
+#endif /* CONFIG_EARLY_PRINTK */