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From: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [PATCH 10/13] powerpc: check cache coherency of kernel vs firmware
Date: Mon, 14 May 2007 14:34:49 +0200
To: David Gibson <david@gibson.dropbear.id.au>
Cc: linuxppc-dev <Linuxppc-dev@ozlabs.org>, Paul Mackerras <paulus@samba.org>
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>> check_cache_coherency() verifies that the cache coherency setting of
>> the kernel (CONFIG_NOT_COHERENT_CACHE) matches that left by the 
>> firmware,
>> as indicated by coherency-off device tree property.
>
> This looks really bogus.  If the firmware reports a coherency state,
> then presumably there's some hardware switch to turn coherency on or
> off.  In which case, can't the kernel just toggle that switch to
> whatever's appropriate for it?

But can the kernel know in all cases what is the
appropriate setting?  This kind of thing is a
typical firmware job.


Segher