linux-kernel - Re: [PATCH -tip] x86,apic: Use PAGE

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Message-ID: <4AF8A0A0.2080800@zytor.com>
Date:	Mon, 09 Nov 2009 15:07:12 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
CC:	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	x86team <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] x86,apic: Use PAGE_SIZE instead of numbers

On 11/08/2009 07:53 AM, Cyrill Gorcunov wrote:
> The whole page is reserved for IO-APIC fixmap
> due to non-cacheable requirement. So lets note
> this explicitly instead of playing with numbers.
> 
> CC: Yinghai Lu <yinghai@...nel.org>
> CC: "Maciej W. Rozycki" <macro@...ux-mips.org>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> ---
> 
> Perhaps I miss something and (4 * 1024) have some special
> meaning?
> 
>  arch/x86/kernel/apic/io_apic.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6.git/arch/x86/kernel/apic/io_apic.c
> =====================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/apic/io_apic.c
> +++ linux-2.6.git/arch/x86/kernel/apic/io_apic.c
> @@ -4144,7 +4144,7 @@ fake_ioapic_page:
>  		idx++;
>  
>  		ioapic_res->start = ioapic_phys;
> -		ioapic_res->end = ioapic_phys + (4 * 1024) - 1;
> +		ioapic_res->end = ioapic_phys + PAGE_SIZE - 1;
>  		ioapic_res++;
>  	}
>  }

In theory we could have more than one ioapic packed into a single page,
and it is also entirely plausible we'll support other page sizes in x86
at some point.  However, it's probably easier to flag something as
PAGE_SIZE and have to fix it up later than have magic constants, so I
think it's probably the right thing to do.

	-hpa
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