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Date: Tue, 20 Aug 2013 11:15:55 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] powerpc iommu: enable multiple TCE requests
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>, Alexander Graf <agraf@suse.de>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, Paul Mackerras <paulus@samba.org>, David Gibson <david@gibson.dropbear.id.au>

Il 20/08/2013 11:13, Benjamin Herrenschmidt ha scritto:
> On Tue, 2013-08-20 at 11:09 +0200, Paolo Bonzini wrote:
>>> Sorry if I miss anything, but is not it what the patch already
>> does? :)
>>
>> No, you need to expose multitce unconditionally in the device tree.
> 
> If I'm not mistaken the multitce kernel side patches are still not
> upstream so I disagree. Exposing it will make Linux use it which means
> that anything running on 3.10 or 3.11 will become very slow.
> 
> So no, multitce should not be exposed if KVM doesn't support it.

Then you have to do it right and:

- provide the infrastructure to enable/disable it from the command line
(which will be enough design effort alone);

- add pseries-1.6 as a synonym of pseries in 1.6.1;

- add pseries-1.7 a synonym of pseries in master;

- add a pseries-1.6 machine type in master that always disables it.

Paolo