linux-kernel - Re: [PATCH 09/22] ARM: LPAE: use 64-bit pgd physical address in switch

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Message-ID: <alpine.LFD.2.02.1208052220060.5231@xanadu.home>
Date:	Sun, 5 Aug 2012 22:35:33 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Cyril Chemparathy <cyril@...com>
cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	Vitaly Andrianov <vitalya@...com>
Subject: Re: [PATCH 09/22] ARM: LPAE: use 64-bit pgd physical address in
 switch_mm()

On Sun, 5 Aug 2012, Cyril Chemparathy wrote:

> On 8/4/2012 3:04 AM, Nicolas Pitre wrote:
> > On Tue, 31 Jul 2012, Cyril Chemparathy wrote:
> > 
> > > This patch modifies the switch_mm() processor functions to use 64-bit
> > > addresses.  We use u64 instead of phys_addr_t, in order to avoid having
> > > config
> > > dependent register usage when calling into switch_mm assembly code.
> > > 
> > > The changes in this patch are primarily adjustments for registers used for
> > > arguments to switch_mm.  The few processor definitions that did use the
> > > second
> > > argument have been modified accordingly.
> > > 
> > > Arguments and calling conventions aside, this patch should be a no-op on
> > > v6
> > > and non-LPAE v7 processors.
> > 
> > NAK.
> > 
> > You just broke all big endian targets, LPAE or not.
> > 
> 
> Indeed.  Thanks.
> 
> Would C-land word swappery on BE do?  Any other ideas on the best approach to
> this?

First, don't use a u64 unconditionally. A phys_addr_t is best for the 
same arguments as before.  Since this is equivalent to a u64 only when 
LPAE is defined, you then only have to care about endian issues in 
proc-v7-3level.S.  And in there you can deal with the issue with 
register aliases just as it is done in lib/div64.S.


Nicolas
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