On Tue, 11 Oct 2011 10:15:34 -0600 Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: > On Tue, Oct 11, 2011 at 1:48 AM, Benjamin Herrenschmidt > <benh@xxxxxxxxxxxxxxxxxxx> wrote: > > > I must admit I don't completely understand what this patch is about, > > other than it will most probably break the way we do resource management > > on powerpc :-) > > > > I don't understand the point about conflicts in scan_slot and I don't > > see what you win by "settling down early". Also keep in mind that the > > resources read from the device need to be remapped on some archs like > > powerpc which we do from a header quirk at the moment. > > These patches only deal with root bus resources, i.e., the > non-architected PCI host bridge windows. They don't have anything to > do with normal PCI BARs. > > MIPS sets up root buses differently than powerpc, so it has a problem > that powerpc doesn't have. Here's the original MIPS flow (before this > series): > > pci_scan_bus > pci_scan_bus_parented > pci_create_bus <-- A create root bus > pci_scan_child_bus > pci_scan_slot > pci_scan_single_device > pci_scan_device > pci_setup_device > pci_fixup_device (pci_fixup_early) <-- B > pci_device_add > pci_fixup_device (pci_fixup_header) <-- C > pcibios_fixup_bus <-- D fill in root bus resources > > At point A, we allocate a struct pci_bus for the root bus. > pci_create_bus() fills in defaults for the resources available on that > bus: ioport_resource and iomem_resource, which cover all possible > address space. Later at point D, we replace those defaults with the > correct resources (hose->io_resource and hose->mem_resource in this > MIPS case). > > The problem is that the root bus resources are wrong during the > interval between A and D. Anything that looks at them may break. In > the case Deng-Cheng found, the quirk_piix4_acpi() fixup at point C > claimed a region, which incorrectly became the child of > ioport_resource instead of host->io_resource. > > Deng-Cheng's patches close this window by basically combining the > fixup at D with the root bus creation at A. > > Powerpc doesn't have the same problem because it calls > pci_create_bus() directly so it can fix the root bus resources with > pcibios_setup_phb_resources() *before* it scans the bus. > > Even though powerpc and many other architectures don't have the MIPS > problem, I think it's worth changing the code because the existing > pattern is poor. In almost all cases, we know what the host bridge > apertures are before we create the root bus. It's error-prone to have > pci_create_bus() fill in default resources, then rely on the > architecture to fix that up later. I think it's better to supply the > resources up front. Ben, with the above explained are you ok with this change? Thanks, -- Jesse Barnes, Intel Open Source Technology Center
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