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[PATCH] MIPS: Enable interrupts before WAIT instruction.

To: linux-mips@linux-mips.org, ralf@linux-mips.org
Subject: [PATCH] MIPS: Enable interrupts before WAIT instruction.
From: David Daney <ddaney.cavm@gmail.com>
Date: Thu, 2 May 2013 13:48:12 -0700
Cc: Linus Torvalds <torvalds@linux-foundation.org>, linux-kernel@vger.kernel.org, David Daney <david.daney@cavium.com>, Thomas Gleixner <tglx@linutronix.de>, Jonas Gorski <jogo@openwrt.org>
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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


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