On 06/05/2012 02:02 PM, Richard Yang wrote: > On Mon, Jun 04, 2012 at 10:18:46PM -0700, Yinghai Lu wrote: >> On Mon, Jun 4, 2012 at 9:37 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: >>> That's true, but I don't think it answers the question. If we have: >>> >>> pci_bus->bridge == pci_bus->self->dev >>> >>> why would we need both "self" and "bridge"? It would be interesting >>> to try to remove "bridge" and replace uses of it with "self->dev". >> >> then how about root bus? >> >> root bus ->self should be NULL. >> >> root bus ->bridge is to the hostbridge->dev. >> >> Yinghai > > Agree, root_pci_bus->self is NULL, and root_pci_bus->bridge point to a > solo device structure, not in hostbridge. > > BTW, if the dev is the hostbrige->dev, why not pci_host_bridge contain a > field "dev"? > > And, why root bus differs with other bus a lot? > Both root bus and other bus use self/bridge point to the "PCI BRIDGE" > device. > I think we can determine whether this is a root bus by bus->parent? Hi Richard, There's fundamental difference between root bridge and pci bridge. A PCI bridge is a PCI to PCI bridge. It's presented as a PCI device on the primary bus and hosts the secondary bus. So the secondary bus is associated with the PCI device on the primary bus through pci_bus->self and pci_bus->device. A root bridge is a system bus to PCI bus bridge, which connects PCI domain to system bus domain. The primary side is the system bus and the secondary side is a PCI bus, so there's a PCI bus associated with a root bridge, but there's no PCI device for the root bridge because it's primary side is system bus, out of the PCI domain. pci_bus->bridge is a common abstraction of the device associated with a PCI bus, no matter it's a host bridge or P2P bridge. So we don't need to distinguish between host bridge and pci bridge when we want to hold a reference to the device associated with a PCI bus. Thanks! Gerry -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
