On 11/14/2011 01:14 PM, Matthew Wilcox wrote: > On Mon, Nov 14, 2011 at 09:44:50AM -0500, Prarit Bhargava wrote: >> On 11/11/2011 03:35 PM, Don Dutile wrote: >> We should make it work automatically, either with >>>> some sort of machine-dependent quirk, or (preferably) with a change to >>>> the generic algorithm so it can handle these "broken" topologies along >>>> with all the correct ones. >> >> The problem is when I'm examining "this" PCIE bridge I have no knowledge of the remaining hierarchy below it. In order to find the broken topology we need to do a two pass enumeration (NO.) or minimally query all possible devices immediately connected to it. If we do that then what is the purpose of the only_one_child() check? > > We have enough information to do this quirk. > > pci_scan_slot calls pci_scan_single_device() for the devfn 0. > We can look at the device we found and quirk the parent device. > Something like this ... > > int pci_scan_slot(struct pci_bus *bus, int devfn) > [...] > dev = pci_scan_single_device(bus, devfn); > if (!dev) > return 0; > if (!dev->is_added) > nr++; > + /* Quirk to fix NEC/Stratus broken PCIe topologies */ > + if ((dev->pcie_type == PCI_EXP_TYPE_DOWNSTREAM) && > + (bus->self->pcie_type == PCI_EXP_TYPE_DOWNSTREAM)) > + bus->self->pcie_type = PCI_EXP_TYPE_UPSTREAM; I'm undoubtedly missing something obvious here, or I'm being dense. This only works if there is a single Down bridge connected to a single Down bridge. What Stratus/NEC has is a single Up bridge (02:00.0) connected to a Up bridge (03:00.0) and a Down bridge (03:01.0), which we know to be illegal in PCIE. So the scan of the first bridge, 03:00.0 works and no fixup is done. The code still misses the second bridge, 03:01.0. Again -- I'm likely not seeing the bigger picture here or I'm missing something obvious why your patch works ... care to explain in detail? > > As an aside, I'm quite shocked that this patch has been in the kernel > for almost two years and this is the first time anybody's tested it on > one of these systems. > Heh ... we recently have asked some of our partners to monitor upstream more closely to avoid last minute "gotchyas" exactly like this one. P. -- 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
