[AVR32] NMI debugging

Change the NMI handler to use the die notifier chain to signal anyone
who cares. Add a simple "nmi debugger" which hooks into this chain and
that may dump registers, task state, etc. when it happens.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

arch/avr32/kernel/Makefile

@@ -12,3 +12,4 @@ obj-y				+= init_task.o switch_to.o cpu.o
 obj-$(CONFIG_MODULES)		+= module.o avr32_ksyms.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
+obj-$(CONFIG_NMI_DEBUGGING)	+= nmi_debug.o

arch/avr32/kernel/irq.c

@@ -25,6 +25,17 @@ void ack_bad_irq(unsigned int irq)
 	printk("unexpected IRQ %u\n", irq);
 }
 
+/* May be overridden by platform code */
+int __weak nmi_enable(void)
+{
+	return -ENOSYS;
+}
+
+void __weak nmi_disable(void)
+{
+
+}
+
 #ifdef CONFIG_PROC_FS
 int show_interrupts(struct seq_file *p, void *v)
 {

arch/avr32/kernel/nmi_debug.c

@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2007 Atmel Corporation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/delay.h>
+#include <linux/kdebug.h>
+#include <linux/notifier.h>
+#include <linux/sched.h>
+
+#include <asm/irq.h>
+
+enum nmi_action {
+	NMI_SHOW_STATE	= 1 << 0,
+	NMI_SHOW_REGS	= 1 << 1,
+	NMI_DIE		= 1 << 2,
+	NMI_DEBOUNCE	= 1 << 3,
+};
+
+static unsigned long nmi_actions;
+
+static int nmi_debug_notify(struct notifier_block *self,
+		unsigned long val, void *data)
+{
+	struct die_args *args = data;
+
+	if (likely(val != DIE_NMI))
+		return NOTIFY_DONE;
+
+	if (nmi_actions & NMI_SHOW_STATE)
+		show_state();
+	if (nmi_actions & NMI_SHOW_REGS)
+		show_regs(args->regs);
+	if (nmi_actions & NMI_DEBOUNCE)
+		mdelay(10);
+	if (nmi_actions & NMI_DIE)
+		return NOTIFY_BAD;
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block nmi_debug_nb = {
+	.notifier_call = nmi_debug_notify,
+};
+
+static int __init nmi_debug_setup(char *str)
+{
+	char *p, *sep;
+
+	register_die_notifier(&nmi_debug_nb);
+	if (nmi_enable()) {
+		printk(KERN_WARNING "Unable to enable NMI.\n");
+		return 0;
+	}
+
+	if (*str != '=')
+		return 0;
+
+	for (p = str + 1; *p; p = sep + 1) {
+		sep = strchr(p, ',');
+		if (sep)
+			*sep = 0;
+		if (strcmp(p, "state") == 0)
+			nmi_actions |= NMI_SHOW_STATE;
+		else if (strcmp(p, "regs") == 0)
+			nmi_actions |= NMI_SHOW_REGS;
+		else if (strcmp(p, "debounce") == 0)
+			nmi_actions |= NMI_DEBOUNCE;
+		else if (strcmp(p, "die") == 0)
+			nmi_actions |= NMI_DIE;
+		else
+			printk(KERN_WARNING "NMI: Unrecognized action `%s'\n",
+				p);
+		if (!sep)
+			break;
+	}
+
+	return 0;
+}
+__setup("nmi_debug", nmi_debug_setup);

arch/avr32/kernel/traps.c

@@ -9,6 +9,7 @@
 #include <linux/bug.h>
 #include <linux/init.h>
 #include <linux/kallsyms.h>
+#include <linux/kdebug.h>
 #include <linux/module.h>
 #include <linux/notifier.h>
 #include <linux/sched.h>
@@ -107,9 +108,23 @@ void _exception(long signr, struct pt_regs *regs, int code,
 
 asmlinkage void do_nmi(unsigned long ecr, struct pt_regs *regs)
 {
-	printk(KERN_ALERT "Got Non-Maskable Interrupt, dumping regs\n");
-	show_regs_log_lvl(regs, KERN_ALERT);
-	show_stack_log_lvl(current, regs->sp, regs, KERN_ALERT);
+	int ret;
+
+	nmi_enter();
+
+	ret = notify_die(DIE_NMI, "NMI", regs, 0, ecr, SIGINT);
+	switch (ret) {
+	case NOTIFY_OK:
+	case NOTIFY_STOP:
+		return;
+	case NOTIFY_BAD:
+		die("Fatal Non-Maskable Interrupt", regs, SIGINT);
+	default:
+		break;
+	}
+
+	printk(KERN_ALERT "Got NMI, but nobody cared. Disabling...\n");
+	nmi_disable();
 }
 
 asmlinkage void do_critical_exception(unsigned long ecr, struct pt_regs *regs)