MIPS: Add NMI notifier

Allow the board support code to register a raw notifier callback for
NMI, similar to what is done for CU2 exceptions.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2958/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/traps.h

@@ -25,4 +25,16 @@ extern void (*board_nmi_handler_setup)(void);
 extern void (*board_ejtag_handler_setup)(void);
 extern void (*board_bind_eic_interrupt)(int irq, int regset);
 
+extern int register_nmi_notifier(struct notifier_block *nb);
+
+#define nmi_notifier(fn, pri)						\
+({									\
+	static struct notifier_block fn##_nb = {			\
+		.notifier_call = fn,					\
+		.priority = pri						\
+	};								\
+									\
+	register_nmi_notifier(&fn##_nb);				\
+})
+
 #endif /* _ASM_TRAPS_H */

arch/mips/kernel/traps.c

@@ -1339,9 +1339,18 @@ void ejtag_exception_handler(struct pt_regs *regs)
 
 /*
  * NMI exception handler.
+ * No lock; only written during early bootup by CPU 0.
  */
+static RAW_NOTIFIER_HEAD(nmi_chain);
+
+int register_nmi_notifier(struct notifier_block *nb)
+{
+	return raw_notifier_chain_register(&nmi_chain, nb);
+}
+
 NORET_TYPE void ATTRIB_NORET nmi_exception_handler(struct pt_regs *regs)
 {
+	raw_notifier_call_chain(&nmi_chain, 0, regs);
 	bust_spinlocks(1);
 	printk("NMI taken!!!!\n");
 	die("NMI", regs);