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Date:	Wed, 28 Feb 2007 22:18:50 +0000
From:	Ralf Baechle <ralf@linux-mips.org>
To:	Marc St-Jean <Marc_St-Jean@pmc-sierra.com>
Cc:	Thiemo Seufer <ths@networkno.de>,
	Andrew Sharp <tigerand@gmail.com>, linux-mips@linux-mips.org
Subject: Re: [PATCH 2/5] mips: PMC MSP71xx mips common
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On Wed, Feb 28, 2007 at 01:35:32PM -0800, Marc St-Jean wrote:

> Ralf Baechle wrote:
> > On Tue, Feb 27, 2007 at 05:38:41PM +0000, Thiemo Seufer wrote:
> > 
> >  > Something like
> >  >
> >  > #if LOADADDR == 0xffffffff80000000
> >  >       .fill   0x400
> >  > #endif
> >  >
> >  > but by defining an appropriate name in arch/mips/Makefile instead of
> >  > externalizing the load-y/LOADADDR there.
> > 
> > Basically a good idea but it will fail for 64-bit kernels so the test
> > would need to be extended to cover XKPHYS as well.  Also R2 processors
> > which have the c0_ebase registers do no need to reserve space for
> > exception handlers as they can easily move them elsewhere.
> > 
> >   Ralf
> 
> Hi Ralf,
> 
>  From your description it sounds like not all R2 CPUs have c0_ebase registers?
> 
> I don't know how to check for c0_ebase from the pre-processor, the test below
> assumes they all do.

Sorry for being ambigous.  All R2 processors have ebase.  However Linux
happens to support older processors as well, that was my point.

> How about something like:
> 
> #if (defined(CONFIG_SYS_HAS_CPU_MIPS32_R1) && \
>                  VMLINUX_LOAD_ADDRESS == CKSEG0) || \
>          ((defined(CONFIG_SYS_HAS_CPU_MIPS64_R1) || defined(CONFIG_SYS_HAS_CPU_MIPS64_R2)) && \
>                  VMLINUX_LOAD_ADDRESS == XKPHYS)
> 	.fill 0x400
> #endif

There are several potencial addresses in XKPHYS, so if anything:

#if !defined(CONFIG_CPU_MIPSR2) && \
    ((VMLINUX_LOAD_ADDRESS == CKSEG0) || \
     (VMLINUX_LOAD_ADDRESS & 0xc7ffffffffffffffUL) == XKPHYS)

However even where ebase actually exists there might be reasons not to use
it.  So a config option might be the safe thing to do.

  Ralf