[PATCH] MIPS: Enable interrupts before WAIT instruction.

[David Daney <ddaney.cavm@gmail.com>]

From: David Daney <david.daney@cavium.com>

As noted by Thomas Gleixner:

   commit cdbedc61c8 (mips: Use generic idle loop) broke MIPS as I did
   not realize that MIPS wants to invoke the wait instructions with
   interrupts enabled.

Instead of enabling interrupts in arch_cpu_idle() as Thomas' initial
patch does, we follow Linus' suggestion of doing it in the assembly
code to prevent the compiler from rearranging things.

Signed-off-by: David Daney <david.daney@cavium.com>
Reported-by: EunBong Song <eunb.song@samsung.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jonas Gorski <jogo@openwrt.org>
---

This is only very lightly tested, we need more testing before
declaring it the definitive fix.

 arch/mips/kernel/genex.S | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index ecb347c..57cda9a 100644
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -132,12 +132,13 @@ LEAF(r4k_wait)
 	.set	noreorder
 	/* start of rollback region */
 	LONG_L	t0, TI_FLAGS($28)
-	nop
 	andi	t0, _TIF_NEED_RESCHED
 	bnez	t0, 1f
 	 nop
-	nop
-	nop
+	/* Enable interrupts so WAIT will complete */
+	mfc0	t0, CP0_STATUS
+	ori	t0, ST0_IE
+	mtc0	t0, CP0_STATUS
 	.set	mips3
 	wait
 	/* end of rollback region (the region size must be power of two) */
-- 
1.7.11.7