sh: nmi_debug support.

This implements support for NMI debugging that was shamelessly copied
from the avr32 port. A bit of special magic is needed in the interrupt
exception path given that the NMI exception handler is stubbed in to the
regular exception handling table despite being reported in INTEVT. So we
mangle the lookup and kick off an EXPEVT-style exception dispatch from
the INTEVT path for exceptions that do_IRQ() has no chance of handling.
As a result, we also drop the evt2irq() conversion from the do_IRQ() path
and just do it in assembly.

Signed-off-by: Paul Mundt <[e-mail]>

Documentation/kernel-parameters.txt

···
 			of returning the full 64-bit number.
 			The default is to return 64-bit inode numbers.
 
-	nmi_debug=	[KNL,AVR32] Specify one or more actions to take
+	nmi_debug=	[KNL,AVR32,SH] Specify one or more actions to take
 			when a NMI is triggered.
 			Format: [state][,regs][,debounce][,die]
 

arch/sh/include/asm/kdebug.h

···
 /* Grossly misnamed. */
 enum die_val {
 	DIE_TRAP,
+	DIE_NMI,
 	DIE_OOPS,
 };
 

arch/sh/include/asm/system.h

···
 BUILD_TRAP_HANDLER(singlestep);
 BUILD_TRAP_HANDLER(fpu_error);
 BUILD_TRAP_HANDLER(fpu_state_restore);
-BUILD_TRAP_HANDLER(unwinder);
+BUILD_TRAP_HANDLER(nmi);
 
 #ifdef CONFIG_BUG
 extern void handle_BUG(struct pt_regs *);

arch/sh/kernel/Makefile

···
 endif
 
 obj-y	:= debugtraps.o dumpstack.o idle.o io.o io_generic.o irq.o	\
-	   machvec.o process_$(BITS).o ptrace_$(BITS).o setup.o 	\
-	   signal_$(BITS).o sys_sh.o sys_sh$(BITS).o syscalls_$(BITS).o	\
-	   time.o topology.o traps.o traps_$(BITS).o unwinder.o
+	   machvec.o nmi_debug.o process_$(BITS).o ptrace_$(BITS).o	\
+	   setup.o signal_$(BITS).o sys_sh.o sys_sh$(BITS).o		\
+	   syscalls_$(BITS).o time.o topology.o traps.o			\
+	   traps_$(BITS).o unwinder.o
 
 obj-y				+= cpu/
 obj-$(CONFIG_VSYSCALL)		+= vsyscall/

arch/sh/kernel/cpu/sh3/entry.S

···
 	mov.l	2f, r4
 	mov.l	3f, r9
 	mov.l	@r4, r4		! pass INTEVT vector as arg0
+
+	shlr2	r4
+	shlr	r4
+	mov	r4, r0		! save vector->jmp table offset for later
+
+	shlr2	r4		! vector to IRQ# conversion
+	add	#-0x10, r4
+
+	cmp/pz	r4		! is it a valid IRQ?
+	bt	10f
+
+	/*
+	 * We got here as a result of taking the INTEVT path for something
+	 * that isn't a valid hard IRQ, therefore we bypass the do_IRQ()
+	 * path and special case the event dispatch instead.  This is the
+	 * expected path for the NMI (and any other brilliantly implemented
+	 * exception), which effectively wants regular exception dispatch
+	 * but is unfortunately reported through INTEVT rather than
+	 * EXPEVT.  Grr.
+	 */
+	mov.l	6f, r9
+	mov.l	@(r0, r9), r9
 	jmp	@r9
+	 mov	r15, r8		! trap handlers take saved regs in r8
+
+10:
+	jmp	@r9		! Off to do_IRQ() we go.
 	 mov	r15, r5		! pass saved registers as arg1
 
 ENTRY(exception_none)

arch/sh/kernel/cpu/sh3/ex.S

···
 	.long	system_call	! Unconditional Trap	 /* 160 */
 	.long	exception_error	! reserved_instruction (filled by trap_init) /* 180 */
 	.long	exception_error	! illegal_slot_instruction (filled by trap_init) /*1A0*/
-ENTRY(nmi_slot)
-	.long	kgdb_handle_exception	/* 1C0 */	! Allow trap to debugger
-ENTRY(user_break_point_trap)
+	.long	nmi_trap_handler	/* 1C0 */	! Allow trap to debugger
 	.long	break_point_trap	/* 1E0 */
 
 	/*

arch/sh/kernel/irq.c

···
 #endif
 
 	irq_enter();
-	irq = irq_demux(evt2irq(irq));
+	irq = irq_demux(irq);
 
 #ifdef CONFIG_IRQSTACKS
 	curctx = (union irq_ctx *)current_thread_info();

arch/sh/kernel/nmi_debug.c

···
+/*
+ * 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 <linux/hardirq.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 (*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/sh/kernel/traps.c

···
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/uaccess.h>
+#include <linux/hardirq.h>
 #include <asm/unwinder.h>
 #include <asm/system.h>
 
···
 #endif
 
 	force_sig(SIGTRAP, current);
+}
+
+BUILD_TRAP_HANDLER(nmi)
+{
+	TRAP_HANDLER_DECL;
+
+	nmi_enter();
+
+	switch (notify_die(DIE_NMI, "NMI", regs, 0, vec & 0xff, SIGINT)) {
+	case NOTIFY_OK:
+	case NOTIFY_STOP:
+		break;
+	case NOTIFY_BAD:
+		die("Fatal Non-Maskable Interrupt", regs, SIGINT);
+	default:
+		printk(KERN_ALERT "Got NMI, but nobody cared. Ignoring...\n");
+		break;
+	}
+
+	nmi_exit();
 }