linux-kernel - Re: [PATCH] x86/apic: Justification for disabling IO APIC before Local APIC

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Message-ID: <20131205085451.GA13377@gmail.com>
Date:	Thu, 5 Dec 2013 09:54:51 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Fenghua Yu <fenghua.yu@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH] x86/apic: Justification for disabling IO APIC before
 Local APIC


* Fenghua Yu <fenghua.yu@...el.com> wrote:

> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> Since erratum AVR31 in "Intel Atom Processor C2000 Product Family
> Specification Update" is published, I add a justification comment for
> disabling IO APIC before Local APIC (commit 522e6646).
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> ---
>  arch/x86/kernel/reboot.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index da3c599..c752cb4 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -558,6 +558,17 @@ void native_machine_shutdown(void)
>  {
>  	/* Stop the cpus and apics */
>  #ifdef CONFIG_X86_IO_APIC
> +	/*
> +	 * Disabling IO APIC before local APIC is a workaround for
> +	 * erratum AVR31 in "Intel Atom Processor C2000 Product Family
> +	 * Specification Update". In this situation, interrupts that target
> +	 * a Logical Processor whose Local APIC is either in the process of
> +	 * being hardware disabled or software disabled are neither delivered
> +	 * nor discarded. When this erratum occurs, the processor may hang.
> +	 *
> +	 * Even without the erratum, it still makes sense to quiet IO APIC
> +	 * before disabling Local APIC.
> +	 */
>  	disable_IO_APIC();
>  #endif

Looks good to me, except that patch titles should start with verbs, 
i.e. something like:

  x86/apic/doc: Add justification for disabling IO APIC before Local APIC

Which makes for a much more fluid reading of shortlogs etc.

Unless you sentences without verbs.
          ^-------------------------------------------like

;-)

Thanks,

	Ingo
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