Re: [Qemu-devel] [PATCH v3] hw/arm/virt: Add high MMIO PCI region

[Pavel Fedin <p.fedin@samsung.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