[MIPS] ret_from_irq adjustment

Make sure that RA on top of interrupt stack is an address of ret_from_irq,
so that dump_stack etc. can trace info interrupted context.

Also this patch fixes except_vec_vi_handler and __smtc_ipi_vector which
seems broken.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S
index e93e43e..417c08a 100644
--- a/arch/mips/kernel/entry.S
+++ b/arch/mips/kernel/entry.S
@@ -20,10 +20,7 @@
 #include <asm/mipsmtregs.h>
 #endif
 
-#ifdef CONFIG_PREEMPT
-	.macro	preempt_stop
-	.endm
-#else
+#ifndef CONFIG_PREEMPT
 	.macro	preempt_stop
 	local_irq_disable
 	.endm
@@ -32,9 +29,16 @@
 
 	.text
 	.align	5
+FEXPORT(ret_from_irq)
+	LONG_S	s0, TI_REGS($28)
+#ifdef CONFIG_PREEMPT
+FEXPORT(ret_from_exception)
+#else
+	b	_ret_from_irq
 FEXPORT(ret_from_exception)
 	preempt_stop
-FEXPORT(ret_from_irq)
+#endif
+FEXPORT(_ret_from_irq)
 	LONG_L	t0, PT_STATUS(sp)		# returning to kernel mode?
 	andi	t0, t0, KU_USER
 	beqz	t0, resume_kernel