Re: [PATCH-for-10.0 0/8] hw/boards: Remove legacy MachineClass::pci_allow_0_address flag

[Peter Maydell]

On Mon, 25 Nov 2024 at 14:06, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>
> This series aims to remove a legacy field from
> MachineClass.
>
> Rather than a global exposed to all machines,
> use a pci-bus specific flag on each machine
> requiering it.

Should this be a property of the PCI controller, rather
than on the PCI bus? Presumably on the machines that
don't allow a 0 PCI BAR address this happens because the
PCI controller refuses to map BARs at that address.

TBH the commit message for e402463073 suggests to me
that "allow address zero" should be the default and
either specific machines should forbid it or else we
should figure out what goes wrong with them, if the
problem is caused by some bug in QEMU. The commit message's
mention of "fix PCI memory priorities" suggests to me
that this is a QEMU bug, and that it ought to be possible
to have the machine set up such that you *can* map the
BAR at address 0, it's merely invisible to the guest because
some other machine devices have higher priority and are
visible "on top" of it instead.

thanks
-- PMM