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

[Alexander Gordeev <agordeev@redhat.com>]

On Tue, Oct 13, 2015 at 09:16:34AM +0100, Peter Maydell wrote:
> On 13 October 2015 at 07:31, Alexander Gordeev <agordeev@redhat.com> wrote:
> > On Mon, Oct 12, 2015 at 10:03:03PM +0100, Peter Maydell wrote:
> >> On 12 October 2015 at 21:55, Alexander Gordeev <agordeev@redhat.com> 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.

I will post v2 with an updated changelog then.

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

I am CC-ing Laurent Vivier who introduced the flag.

But IMO it *is* a machine property, not PCI controller's
one, unless I am missing something.

Thanks!

> thanks
> -- PMM

-- 
Regards,
Alexander Gordeev
agordeev@redhat.com