From: Ralf Baechle <ralf@linux-mips.org>
To: Kumar Gala <galak@kernel.crashing.org>
Cc: davem@davemloft.net, wli@holomorphy.com, mingo@redhat.com,
linux-kernel@vger.kernel.org,
Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: use of fixmap on non-x86/sh?
Date: Sat, 8 Dec 2007 20:44:26 +0000 [thread overview]
Message-ID: <20071208204426.GC3361@linux-mips.org> (raw)
In-Reply-To: <D16EA8BE-3C87-4345-8832-AB6112EE0FEA@kernel.crashing.org>
On Fri, Nov 30, 2007 at 04:14:55PM -0600, Kumar Gala wrote:
> Ben and I are talking about using fixmap on ppc for similar applications to
> it use on x86. However in poking around other arch's (sparc, mips) they
> appear to have some support but not as complete as x86.
>
> For example both SPARC & MIPS reference __set_fixmap() in asm/fixmap.h but
> I can't find an implementation on either.
>
> So I was wondering if there was some reason fixmap isn't as well supported
> or if its just used for a specific function on those SPARC, MIPS, etc. and
> they dont need as much functionality out of it as x86 does.
MIPS uses fixmap for two purposes:
o In some cases it is possibly to avoid or optimize a cacheflush by creating
a temporary mapping. The mechanism works very similar to what x86 and
MIPS use for atomic kmaps.
o Highmem.
Both manipulate pagetables directly or even insert entries directly into
the TLB without pagetables as intermediate stage so __set_fixmap is indeed
unused.
Ralf
prev parent reply other threads:[~2007-12-08 20:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-30 22:14 use of fixmap on non-x86/sh? Kumar Gala
2007-12-01 1:03 ` Paul Mundt
2007-12-01 5:15 ` Benjamin Herrenschmidt
2007-12-08 20:44 ` Ralf Baechle [this message]
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