On Fri, Jul 26, 2013 at 05:43:44PM -0500, Scott Wood wrote:
> On 07/25/2013 07:54:53 AM, Kevin Hao wrote:
> >The reason is that the ppc kernel assume that the BARs starting
> >at 0 is unset and will reassign it later. There is a bug in the
> >previous
> >kernel, so the kernel maybe not work well for qemu in this case. But I
> >think this has been fixed by the commit c5df457f (powerpc/pci:
> >Check the
> >bus address instead of resource address in pcibios_fixup_resources).
> 
> What ensures that the reassignment will not assign zero?

In function pcibios_resource_survey() we will reserve the low IO area
before reassignment. Please see the following comments and codes in this
function.

        /* Before we start assigning unassigned resource, we try to reserve
         * the low IO area and the VGA memory area if they intersect the
         * bus available resources to avoid allocating things on top of them
         */
        if (!pci_has_flag(PCI_PROBE_ONLY)) {
                list_for_each_entry(b, &pci_root_buses, node)
                        pcibios_reserve_legacy_regions(b);
        }    


Thanks,
Kevin

> 
> I'm not doubting the result that it does, but I'm having a hard time
> seeing it in the code.
> 
> Or are you saying that the resource assignment code will run twice,
> rather than just saying that we won't trust the firmware when we
> find zero?
> 
> -Scott