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Date: Wed, 8 Nov 2017 19:52:12 -0200
From: Eduardo Habkost <ehabkost@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] hw: add .min_cpus and .default_cpus fields
 to machine_class
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To: Richard Henderson <richard.henderson@linaro.org>
Cc: "Emilio G. Cota" <cota@braap.org>, qemu-devel@nongnu.org, Peter Maydell <peter.maydell@linaro.org>, Thomas Huth <thuth@redhat.com>, qemu-arm@nongnu.org, Igor Mitsyanko <i.mitsyanko@gmail.com>, Alistair Francis <alistair.francis@xilinx.com>, "Edgar E . Iglesias" <edgar.iglesias@gmail.com>, Marcel Apfelbaum <marcel@redhat.com>, Igor Mammedov <imammedo@redhat.com>

On Wed, Nov 08, 2017 at 10:29:43PM +0100, Richard Henderson wrote:
> On 11/06/2017 09:13 PM, Emilio G. Cota wrote:
> > Subject: [PATCH] qom: move CPUClass.tcg_initialize to a global
> > 
> > 55c3cee ("qom: Introduce CPUClass.tcg_initialize", 2017-10-24)
> > introduces a per-CPUClass bool that we check so that the target CPU
> > is initialized for TCG only once. This works well except when
> > we end up creating more than one CPUClass, in which case we end
> > up incorrectly initializing TCG more than once, i.e. once for
> > each CPUClass.
> > 
> > This can be replicated with:
> >   $ aarch64-softmmu/qemu-system-aarch64 -machine xlnx-zcu102 -smp 6 \
> >       -global driver=xlnx,,zynqmp,property=has_rpu,value=on
> > In this case the class name of the "RPUs" is prefixed by "cortex-r5-",
> > whereas the "regular" CPUs are prefixed by "cortex-a53-". This
> > results in two CPUClass instances being created.
> > 
> > Fix it by introducing a static variable, so that only the first
> > target CPU being initialized will initialize the target-dependent
> > part of TCG, regardless of CPUClass instances.
> 
> Hah!
> 
> So, I had been thinking of the xylinx ARM + Microblaze case, where we really do
> need two different initializations.  I never imagined that two different ARM
> parts had different CPUClasses.

Is xylinx ARM + Microblaze something that already works (and
would be broken by this patch), or something planned for the
future?

> 
> So I guess it's my initial patch that unified this that's more buggy than not.

We still have the option of reverting the original patch, but (if
it doesn't break anything) this patch looks like a simpler fix
for 2.11 than a full revert.

-- 
Eduardo