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From: Pavel Fedin <p.fedin@samsung.com>
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Date: Mon, 27 Jul 2015 17:36:07 +0300
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Subject: Re: [Qemu-devel] [PATCH v3] hw/arm/virt: Add high MMIO PCI region
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To: 'Igor Mammedov' <imammedo@redhat.com>
Cc: 'Peter Maydell' <peter.maydell@linaro.org>, 'Alexander Graf' <agraf@suse.de>, mst@redhat.com, 'QEMU Developers' <qemu-devel@nongnu.org>, pbonzini@redhat.com

 Hello!

> > +    /* High MMIO space */
> > +    mmio_alias = g_new0(MemoryRegion, 1);
> > +    memory_region_init_alias(mmio_alias, OBJECT(dev), "pcie-mmio-high",
> > +                             mmio_reg, base_mmio_high, size_mmio_high);
> > +    memory_region_add_subregion(get_system_memory(), base_mmio_high, mmio_alias);
> Is there any specific reason to have 2 separate regions vs using 1 like in
>  pc_pci_as_mapping_init()
> using region priority instead of splitting.

 Unfortunately i'm not familiar very well with qemu memory internals. I saw PC code and i know that
it adds PCI region of the size of the whole memory, then adds other things as overlapped regions.
But wouldn't it be some resource waste in this case? I understand that in PC absolutely all "unused"
addresses fall through to PCI, so that any device can plug in there. On ARM this is different, PCI
controller is not a core of the system, it's just one of devices instead. And on our case a huge
part of PCI region between VIRT_PCIE_MMIO and VIRT_PCIE_MMIO_HIGH would never be used. Does it worth
that ?

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia