linux-kernel - Re: [PATCH V4 1/3] x86: introduce CONFIG_X86_DEV_DMA

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Message-ID: <4F873F7F.5080001@zytor.com>
Date:	Thu, 12 Apr 2012 13:47:59 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alessandro Rubini <rubini@...dd.com>
CC:	mingo@...e.hu, akpm@...ux-foundation.org, jbarnes@...tuousgeek.org,
	fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	giancarlo.asnaghi@...com, alan@...ux.intel.com
Subject: Re: [PATCH V4 1/3] x86: introduce CONFIG_X86_DEV_DMA_OPS

On 04/12/2012 01:32 PM, Alessandro Rubini wrote:
>>
>> Not as a compile-time patch.
> 
> Why not? CONFIG_ISA is a compile-time choice. I thought that if you
> compile for non-ISA systems you may reuse the zone mechanism with a
> different split.
> 
> But if not a compile-time thing, would you accept it at run time?
> I feel it's not a beautiful approach, because it must clearly be
> masked by #ifndef CONFIG_ISA or such. Worse, you must know the zone
> split at the beginning, before you scan the PCI bus and find your
> devices.
> 

Compile-time is unacceptable, because it breaks the "one kernel image"
policy we have on x86.  So it should be done at runtime.

	-hpa

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