Re: [Qemu-devel] [PATCH] hw/arm/virt: Allow zero address for PCI IO space

[Peter Maydell]

On 13 October 2015 at 07:31, Alexander Gordeev <address@hidden> wrote:
> On Mon, Oct 12, 2015 at 10:03:03PM +0100, Peter Maydell wrote:
>> On 12 October 2015 at 21:55, Alexander Gordeev <address@hidden> wrote:
>> > Currently PCI IO address 0 is not allowed even though
>> > the IO space starts from 0. As result, PCI IO is not
>> > possible to use at all.
>>
>> I don't see any reason for us not to allow 0 IO addresses,
>> but I'm not sure how your your conclusion follows. It
>> should be entirely possible to map PCI IO to some other
>> address than zero in the IO window, which is what I would
>> have expected the guest to do.
>
> You are right - my changelog is incorrect. The rest of IO
> space should be alright.
>
> However, as 0 IO address is exposed via "ranges" to the guest,
> it must be usable - isn't it? So it either should be allowed
> or the range should be different.

Depends on your point of view. If you take the Linus Torvalds
view that 0 is always an invalid PCI address, then you'll
never try to use it anyway.

In any case, setting pci_allow_0_address is the right thing,
so we can just change the commit message in this patch.

Incidentally, why is this a property on the machine
and not on the PCI controller device?

thanks
-- PMM