linux-kernel - Re: [PATCH] MIPS: Enable interrupts before WAIT instruction.

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Date:	Thu, 2 May 2013 23:04:19 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	David Daney <ddaney.cavm@...il.com>
cc:	linux-mips@...ux-mips.org, ralf@...ux-mips.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, David Daney <david.daney@...ium.com>,
	Jonas Gorski <jogo@...nwrt.org>
Subject: Re: [PATCH] MIPS: Enable interrupts before WAIT instruction.



On Thu, 2 May 2013, David Daney wrote:

> From: David Daney <david.daney@...ium.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.

Yeah, that looks way more sane.

 
> Signed-off-by: David Daney <david.daney@...ium.com>
> Reported-by: EunBong Song <eunb.song@...sung.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Jonas Gorski <jogo@...nwrt.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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