On 29.08.2008 18:27, Stefan Reinauer wrote:
- Carl-Daniel Hailfinger c-d.hailfinger.devel.2006@gmx.net [080829 12:54]:
On 29.08.2008 12:41, Stefan Reinauer wrote:
Carl-Daniel Hailfinger wrote:
* dev->link[0] for a PCI domain is the domain link.* The child of the domain link is the PCI bus device."PCI bus device" - is that the host bridge?
Let me illustrate this with an excerpt of our device tree.
We call pci_domain_scan_bus(dev_domain_0, ...) and dev_domain_0->link[0] is the PCI domain link. However, pci_scan_bus() expects to be called with dev_bus_0->link[0] which equals dev_domain_0->link[0].children->link[0]. "pci bus device" refers to dev_bus_0.
Ok, so why do we have
a) a pci domain b) a pci bus "device" whatever that is supposed to depict c) a pci bridge (host bridge)
all describing the same physical entity.
We had weird stuff in v2, but now it's not fixed, it's just different weird.
Can multiple buses be directly below a domain or do these buses hang off a bridge on a bus? For the latter case, this should be handled by pci_scan_bridge.
A PCI domain is not a physical device. It doesnt even virtually exist on x86, at least not on pre-PCIe systems.
OK, let me rephrase my question and answer it in part withe the help of the relevant standards. Is it possible to have multiple top-level PCI Buses? Yes, but only in the sense that top-level Buses are attached to different Host Bridges.
The PCI-to-PCI Bridge Architecture 1.2 http://www.pcisig.com/members/downloads/specifications/conventional/ppb12.pdf standard says that each PCI Bridge has exactly one primary and one secondary interface, each with exactly one Bus attached. So it is not possible to have multiple PCI Buses directly below a PCI Bridge.
That means for my patch: IFF we only have one top-level PCI Bus (anything else is impossible with only one Host Bridge) my patch is completely correct. However, IFF there are multiple independent Host Bridges which do NOT share a PCI bus, we need to implement a function which iterates over these Host Bridges.
Regards, Carl-Daniel