nios2: add early printk support

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

arch/nios2/Kconfig.debug

@@ -14,4 +14,15 @@ config DEBUG_STACK_USAGE
 
 	  This option will slow down process creation somewhat.
 
+config EARLY_PRINTK
+	bool "Activate early kernel debugging"
+	default y
+	select SERIAL_CORE_CONSOLE
+	depends on SERIAL_ALTERA_JTAGUART_CONSOLE || SERIAL_ALTERA_UART_CONSOLE
+	help
+	  Enable early printk on console
+	  This is useful for kernel debugging when your machine crashes very
+	  early before the console code is initialized.
+	  You should normally say N here, unless you want to debug such a crash.
+
 endmenu

arch/nios2/include/asm/prom.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright Altera Corporation (C) <2015>. All rights reserved
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __ASM_NIOS2_PROM_H__
+#define __ASM_NIOS2_PROM_H__
+
+extern unsigned long __init of_early_console(void);
+
+#endif

arch/nios2/kernel/Makefile

@@ -20,5 +20,6 @@ obj-y	+= syscall_table.o
 obj-y	+= time.o
 obj-y	+= traps.o
 
+obj-$(CONFIG_EARLY_PRINTK)		+= early_printk.o
 obj-$(CONFIG_MODULES)			+= module.o
 obj-$(CONFIG_NIOS2_ALIGNMENT_TRAP)	+= misaligned.o

arch/nios2/kernel/early_printk.c

@@ -0,0 +1,118 @@
+/*
+ * Early printk for Nios2.
+ *
+ * Copyright (C) 2015, Altera Corporation
+ * Copyright (C) 2010, Tobias Klauser <tklauser@distanz.ch>
+ * Copyright (C) 2009, Wind River Systems Inc
+ *   Implemented by fredrik.markstrom@gmail.com and ivarholmqvist@gmail.com
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/console.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/io.h>
+
+#include <asm/prom.h>
+
+static unsigned long base_addr;
+
+#if defined(CONFIG_SERIAL_ALTERA_JTAGUART_CONSOLE)
+
+#define ALTERA_JTAGUART_DATA_REG		0
+#define ALTERA_JTAGUART_CONTROL_REG		4
+#define ALTERA_JTAGUART_CONTROL_WSPACE_MSK	0xFFFF0000
+#define ALTERA_JTAGUART_CONTROL_AC_MSK		0x00000400
+
+#define JUART_GET_CR() \
+	__builtin_ldwio((void *)(base_addr + ALTERA_JTAGUART_CONTROL_REG))
+#define JUART_SET_CR(v) \
+	__builtin_stwio((void *)(base_addr + ALTERA_JTAGUART_CONTROL_REG), v)
+#define JUART_SET_TX(v) \
+	__builtin_stwio((void *)(base_addr + ALTERA_JTAGUART_DATA_REG), v)
+
+static void early_console_write(struct console *con, const char *s, unsigned n)
+{
+	unsigned long status;
+
+	while (n-- && *s) {
+		while (((status = JUART_GET_CR())
+				& ALTERA_JTAGUART_CONTROL_WSPACE_MSK) == 0) {
+#if defined(CONFIG_SERIAL_ALTERA_JTAGUART_CONSOLE_BYPASS)
+			if ((status & ALTERA_JTAGUART_CONTROL_AC_MSK) == 0)
+				return;	/* no connection activity */
+#endif
+		}
+		JUART_SET_TX(*s);
+		s++;
+	}
+}
+
+#elif defined(CONFIG_SERIAL_ALTERA_UART_CONSOLE)
+
+#define ALTERA_UART_TXDATA_REG		4
+#define ALTERA_UART_STATUS_REG		8
+#define ALTERA_UART_STATUS_TRDY		0x0040
+
+#define UART_GET_SR() \
+	__builtin_ldwio((void *)(base_addr + ALTERA_UART_STATUS_REG))
+#define UART_SET_TX(v) \
+	__builtin_stwio((void *)(base_addr + ALTERA_UART_TXDATA_REG), v)
+
+static void early_console_putc(char c)
+{
+	while (!(UART_GET_SR() & ALTERA_UART_STATUS_TRDY))
+		;
+
+	UART_SET_TX(c);
+}
+
+static void early_console_write(struct console *con, const char *s, unsigned n)
+{
+	while (n-- && *s) {
+		early_console_putc(*s);
+		if (*s == '\n')
+			early_console_putc('\r');
+		s++;
+	}
+}
+
+#else
+# error Neither SERIAL_ALTERA_JTAGUART_CONSOLE nor SERIAL_ALTERA_UART_CONSOLE \
+selected
+#endif
+
+static struct console early_console_prom = {
+	.name	= "early",
+	.write	= early_console_write,
+	.flags	= CON_PRINTBUFFER | CON_BOOT,
+	.index	= -1
+};
+
+void __init setup_early_printk(void)
+{
+#if defined(CONFIG_SERIAL_ALTERA_JTAGUART_CONSOLE) ||	\
+	defined(CONFIG_SERIAL_ALTERA_UART_CONSOLE)
+	base_addr = of_early_console();
+#else
+	base_addr = 0;
+#endif
+
+	if (!base_addr)
+		return;
+
+#if defined(CONFIG_SERIAL_ALTERA_JTAGUART_CONSOLE_BYPASS)
+	/* Clear activity bit so BYPASS doesn't stall if we've used JTAG for
+	 * downloading the kernel. This might cause early data to be lost even
+	 * if the JTAG terminal is running.
+	 */
+	JUART_SET_CR(JUART_GET_CR() | ALTERA_JTAGUART_CONTROL_AC_MSK);
+#endif
+
+	early_console = &early_console_prom;
+	register_console(early_console);
+	pr_info("early_console initialized at 0x%08lx\n", base_addr);
+}

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 */

arch/nios2/kernel/setup.c

@@ -139,6 +139,10 @@ void __init setup_arch(char **cmdline_p)
 
 	console_verbose();
 
+#ifdef CONFIG_EARLY_PRINTK
+	setup_early_printk();
+#endif
+
 	memory_start = PAGE_ALIGN((unsigned long)__pa(_end));
 	memory_end = (unsigned long) CONFIG_NIOS2_MEM_BASE + memory_size;