From: David Wragg <dpw@doc.ic.ac.uk>
To: Timur Tabi <ttabi@interactivesi.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: ioremap_nocache problem?
Date: 24 Jan 2001 01:01:29 +0000 [thread overview]
Message-ID: <y7rg0i9epau.fsf@sytry.doc.ic.ac.uk> (raw)
In-Reply-To: <20010123183847Z131216-18594+636@vger.kernel.org>
Timur Tabi <ttabi@interactivesi.com> writes:
> ** Reply to message from Roman Zippel <zippel@fh-brandenburg.de> on
> Tue, 23 Jan 2001 19:12:36 +0100 (MET)
> > ioremap creates a new mapping that shouldn't interfere with MTRR,
> >whereas you can map a MTRR mapped area into userspace. But I'm not
> >sure if it's correct that no flag is set for boot_cpu_data.x86 <=
> >3...
>
> I was under the impression that the "don't cache" bit that
> ioremap_nocache sets overrides any MTRR.
Nope. There's a table explaining how page flags and MTRRs interact in
the Intel x86 manual, volume 3 (it's in section 9.5.1 "Precedence of
Cache Controls" in the fairly recent edition I have here).
For example, with PCD set, PWT clear, and the MTRRs saying WC, the
effective memory type is WC. In addition, there's a note saying this
may change in future models. So you have to set PCD | PWT if you want
to get uncached in all cases.
David Wragg
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prev parent reply other threads:[~2001-01-24 1:01 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-01-23 10:30 Mark Mokryn
2001-01-23 16:53 ` Timur Tabi
2001-01-25 15:16 ` Stephen C. Tweedie
2001-01-25 15:56 ` Timur Tabi
2001-01-25 16:44 ` Roman Zippel
2001-01-25 16:49 ` Timur Tabi
2001-01-26 10:39 ` Stephen C. Tweedie
[not found] ` <20010125165001Z132264-460+11@vger.kernel.org>
2001-01-25 17:04 ` Jeff Hartmann
2001-01-25 17:11 ` Timur Tabi
[not found] ` <E14LpvQ-0008Pw-00@mail.valinux.com>
2001-01-25 17:47 ` Jeff Hartmann
2001-01-25 17:53 ` Timur Tabi
2001-01-26 10:43 ` Stephen C. Tweedie
2001-01-26 16:32 ` Eric W. Biederman
2001-01-26 19:22 ` Timur Tabi
[not found] ` <20010125175308Z130507-460+45@vger.kernel.org>
2001-01-25 18:13 ` Jeff Hartmann
2001-01-25 18:18 ` Timur Tabi
[not found] ` <E14Lqyt-0003z6-00@mail.valinux.com>
2001-01-25 18:46 ` Jeff Hartmann
[not found] ` <200101251556.f0PFuPd01743@mail.redhat.com>
2001-01-26 10:37 ` Stephen C. Tweedie
2001-01-23 18:12 ` Roman Zippel
2001-01-23 18:38 ` Timur Tabi
2001-01-24 0:50 ` David Wragg, David Wragg
2001-01-24 15:14 ` Timur Tabi
[not found] ` <E14LRce-0008FU-00@diver.doc.ic.ac.uk>
2001-01-24 15:39 ` David Wragg
[not found] ` <20010123183847Z131216-18594+636@vger.kernel.org>
2001-01-24 1:01 ` David Wragg [this message]
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