linux-kernel - Re: [PATCH v6] ARM: vfp: Always save VFP state in vfp_pm

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Date:	Mon, 16 Jul 2012 14:34:17 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Colin Cross <ccross@...roid.com>
cc:	linux-arm-kernel@...ts.infradead.org,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Russell King <linux@....linux.org.uk>,
	Barry Song <bs14@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Ido Yariv <ido@...ery.com>, Daniel Drake <dsd@...top.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] ARM: vfp: Always save VFP state in vfp_pm_suspend on
 UP

On Mon, 16 Jul 2012, Colin Cross wrote:

> vfp_pm_suspend should save the VFP state in suspend after
> any lazy context switch.  If it only saves when the VFP is enabled,
> the state can get lost when, on a UP system:
>   Thread 1 uses the VFP
>   Context switch occurs to thread 2, VFP is disabled but the
>      VFP context is not saved
>   Thread 2 initiates suspend
>   vfp_pm_suspend is called with the VFP disabled, and the unsaved
>      VFP context of Thread 1 in the registers
> 
> Modify vfp_pm_suspend to save the VFP context whenever
> vfp_current_hw_state is not NULL.
> 
> Includes a fix from Ido Yariv <ido@...ery.com>, who pointed out that on
> SMP systems, the state pointer can be pointing to a freed task struct if
> a task exited on another cpu, fixed by using #ifdef CONFIG_SMP in the
> new if clause.
> 
> Cc: Russell King <linux@....linux.org.uk>
> Cc: Barry Song <bs14@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Ido Yariv <ido@...ery.com>
> Cc: Daniel Drake <dsd@...top.org>
> Cc: Will Deacon <will.deacon@....com>
> Signed-off-by: Colin Cross <ccross@...roid.com>
> ---
>  arch/arm/vfp/vfpmodule.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
> index 58696192..ce55f05 100644
> --- a/arch/arm/vfp/vfpmodule.c
> +++ b/arch/arm/vfp/vfpmodule.c
> @@ -457,6 +457,12 @@ static int vfp_pm_suspend(void)
>  
>  		/* disable, just in case */
>  		fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
> +	} else if (vfp_current_hw_state[ti->cpu]) {
> +#ifndef CONFIG_SMP
> +		fmxr(FPEXC, fpexc | FPEXC_EN);
> +		vfp_save_state(vfp_current_hw_state[ti->cpu], fpexc);
> +		fmxr(FPEXC, fpexc);
> +#endif
>  	}

Couldn't vfp_sync_hwstate() be used here instead?


Nicolas
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