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From: Kumar Gala <galak@kernel.crashing.org>
To: Kenneth Johansson <kenneth@southpole.se>
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Subject: Re: kexec on e300 core / mpc5121
Date: Thu, 6 Aug 2009 08:58:20 -0500
References: <20090804230605.GA28753@Chamillionaire.breakpoint.cc>
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Cc: linuxppc-dev@ozlabs.org,
	Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
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On Aug 5, 2009, at 5:49 PM, Kenneth Johansson wrote:

> On Wed, 2009-08-05 at 01:06 +0200, Sebastian Andrzej Siewior wrote:
>> I've tried kexec on e300 core which should be easy since it is  
>> possible
>> to disable the MMU on that core. However it does not work.
>
> Is it not possible to disable the mmu on all cpu's that have one ??

Nope.  Book-E class PPC parts always have the mmu.

>> Once I disable the MMU, I can't access my MBAR and print chars on the
>> serial port. Is this "normal" or do I have still some caches on?
>
> Yes cache and mmu is separate. the 5121 is not cache coherent and do  
> not
> limit cache to only memory regions so serial port or any memory mapped
> register is a no no unless you have cache off or cache on and mmu on
> with a correct setting for what address range to cache.
>
> Before you turn off the cache you need to flush out all dirty data.  
> best
> done by simply reading in 32kb of crap from somewhere. otherwise you  
> are
> sure to loose at least the stack and you do not want that.

- k