linux-kernel - Re: [PATCH -mm 0/3] i386 boot: replace boot_ioremap with enhanced bt

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Date:	Tue, 15 Jan 2008 14:39:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Huang, Ying" <ying.huang@...el.com>,
	venkatesh.pallipadi@...el.com, akpm@...ux-foundation.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 0/3] i386 boot: replace boot_ioremap with enhanced
	bt_ioremap

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

> I did a quick scan over the patchset (not quite awake yet, so I may 
> very well have missed something), but it looks like EFI (again!) is 
> the only user of ioremapping before paging_init().  This makes me 
> wonder if that code can't be restructured so that isn't necessary.

i think that in general making access to unmapped memory a bit easier is 
generally a good robustness idea as ACPI could be impacted by it as 
well.

Fundamentally, paging_init() has obvious dependency on "figuring out the 
memory setup" of the box, and "figuring out the memory setup" means 
interpreting various data structures passed in by the BIOS - some of 
which might be in not yet mapped areas or iommu areas (if we have to do 
some early quirk). So having a robust implementation of ioremap_early() 
sounds like a definitive plus.

	Ingo
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