linux-kernel - Re: Adding kmap_atomic_prot_pfn (was: [git pull] drm patches for 2.6.27-rc1)

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Message-Id: <1224818474.7654.429.camel@pasglop>
Date:	Fri, 24 Oct 2008 14:21:14 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Keith Packard <keithp@...thp.com>, mingo@...e.hu,
	nickpiggin@...oo.com.au, airlied@...ux.ie,
	linux-kernel@...r.kernel.org, jbarnes@...tuousgeek.org,
	dri-devel@...ts.sf.net, yinghai@...nel.org
Subject: Re: Adding kmap_atomic_prot_pfn  (was: [git pull] drm patches for
	2.6.27-rc1)

On Thu, 2008-10-23 at 14:24 -0700, Linus Torvalds wrote:
> The whole point of that function has absolutely nothing to do with 
> highmem, and it *must* be useful on non-highmem configurations to be 
> appropriate.
> 
> So I'd much rather create a new <linux/kmap.h> or something. Or just 
> expose this from to <asm/fixmap.h> or something. Let's not confuse
> this 
> with highmem, even if the implementation _historically_ was due to
> that.

Well, on powerpc, we just went (or rather, Kumar just went) through the
oops of implementing fixmap and then kmap on top of it... just because
we wanted kmap_atomic functionality on non-highmem platforms :-) (and
the fixmap approach has some other interesting features).

So yes, I agree. Typically very useful for any 32-bit processor with a
memory mapped PCI Express config space since it's something like 256M of
virtual space to map it all iirc.

Cheers,
Ben.

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