Re: [PATCH v13 10/12] PCI: Assign unassigned bus resources in pci_scan_root_bus()

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2014-09-29 at 15:33 -0600, Bjorn Helgaas wrote:
> > Right and on powerpc and others as well. We need to survey existing
> > resources. We also have a number of platform things that might need
> > to happen before we do the final re-assignment pass.
> 
> That's true today.  But I don't know whether it *has* to be this way
> forever.  On x86, pcibios_resource_survey() throws in E820 information
> (which we know long before we do any PCI enumeration) and some IO-APIC
> resources (it looks like we also know these before PCI enumeration).
> Powerpc has pcibios_reserve_legacy_regions(), but that looks like
> mostly stuff that could be done when we find the host bridge, before
> we enumerate PCI devices below it.

Oh we can probably change that but it's going to be much more work than
just moving the assignment into pci_scan_root_bus(). There are also a
number of subtle and not-so-subtle bits of code that rely on side
effects of the current code such as anything that tests for bus->added
or dev->added. Again, nothing we can't sort out eventually but the
transition might be a bit painful.

We might need to introduce a new flag for platforms converted to the
"new style" generalized resource assignment which we can deprecate once
everybody has moved over.

Cheers,
Ben.