linux-kernel - Re: [PATCH 1/7] arm: use generic fixmap.h

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Date:	Thu, 7 Aug 2014 11:32:07 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Rob Herring <robh@...nel.org>
cc:	Max Filippov <jcmvbkbc@...il.com>,
	Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mark Salter <msalter@...hat.com>, Liu hua <sdu.liu@...wei.com>,
	Rabin Vincent <rabin@....in>,
	Nikolay Borisov <Nikolay.Borisov@....com>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Tomasz Figa <t.figa@...sung.com>,
	Doug Anderson <dianders@...gle.com>,
	Will Deacon <will.deacon@....com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/7] arm: use generic fixmap.h

On Thu, 7 Aug 2014, Rob Herring wrote:

> On Thu, Aug 7, 2014 at 10:15 AM, Max Filippov <jcmvbkbc@...il.com> wrote:
> > Hi,
> >
> > On Wed, Aug 6, 2014 at 11:32 PM, Kees Cook <keescook@...omium.org> wrote:
> >> ARM is different from other architectures in that fixmap pages are indexed
> >> with a positive offset from FIXADDR_START.  Other architectures index with
> >> a negative offset from FIXADDR_TOP.  In order to use the generic fixmap.h
> >
> > Does anybody know if there's any reason why generic fixmap.h uses negative
> > offsets? It complicates things with no obvious benefit if you e.g. try to align
> > virtual address in the fixmap region with physical page color (that's why I've
> > switched xtensa to positive fixmap addressing in v3.17).
> 
> No, but each arch doing it differently is even more annoying.

Why not switching everybody to positive offsets then?


Nicolas
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