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

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Date:	Sat, 14 Apr 2012 13:38:59 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Alessandro Rubini <rubini@...dd.com>, 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


* H. Peter Anvin <hpa@...or.com> wrote:

> 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.

Agreed. CONFIG_ISA is an old mistake - we try not to repeat old 
mistakes.

Thanks,

	Ingo
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