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Subject: Re: 32-bit kernel on PPC64 supported?
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Marvin <marvin24@gmx.de>
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Date: Sat, 19 Jul 2008 08:14:35 +1000
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On Fri, 2008-07-18 at 20:43 +0200, Marvin wrote:
> Hi,
> 
> while trying to cleanup some configs/makefiles for ppc64 I noticed, that 
> CONFIG_POWER4 implies CONFIG_PPC64 and vice versa in all defconfigs.
> So I want to boldly replace CONFIG_POWER4 by CONFIG_PPC64 - ugh.

No, those are different.

CONFIG_PPC64 means a 64 bits kernel.

CONFIG_POWER4 means a 64 bits kernel that only runs on IBM POWER4 and
later (ie, processors conforming to, iirc, version 2.01 or later of
the architecture).

That is, it's legal to have CONFIG_PPC64 and !CONFIG_POWER4, and this
is even necessary if you want to boot on a POWER3 or an RS64 processor.

Now, there also used to be some 32 bits support for POWER4 and G5 but
that has been dropped a while ago.

Cheers,
Ben.