linux-kernel - Re: [PATCH v2 08/25] powerpc/8xx: Map IMMR area with 512k page at a fixed address

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Date:	Fri, 25 Sep 2015 12:09:06 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	'Christophe Leroy' <christophe.leroy@....fr>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	"Michael Ellerman" <mpe@...erman.id.au>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 08/25] powerpc/8xx: Map IMMR area with 512k page at a
 fixed address

On Fri, 2015-09-25 at 14:46 +0000, David Laight wrote:
> From: Scott Wood
> > Sent: 24 September 2015 21:14
> > > Isn't this a more general problem?
> > > 
> > > If there are multiple remap requests for the same physical page
> > > shouldn't the kernel be just increasing a reference count somewhere
> > > and returning address in the same virtual page?
> > > This should probably happen regardless of the address.
> > > I presume it must be done for cacheable mappings.
> > 
> > Why would you assume that?
> 
> Because 'really horrid (tm)' things happen on some cache
> architectures if you map the same physical address to
> multiple virtual addresses.

PPC is not such an architecture.

-Scott

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