On Fri, Dec 01, 2017 at 06:27:10PM -0600, Bjorn Helgaas wrote: > From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > PCIe Downstream Ports normally have only a Device 0 below them. To > optimize enumeration, we don't scan for other devices *unless* the > PCI_SCAN_ALL_PCIE_DEVS flag is set by set by quirks or the > "pci=pcie_scan_all" kernel parameter. > > Previously PCI_SCAN_ALL_PCIE_DEVS only affected scanning below Switch > Downstream Ports, not Root Ports. > > But the "Nemo" system, also known as the AmigaOne X1000, has a PA Semi Root > Port whose link leads to an AMD/ATI SB600 South Bridge. The Root Port is a > PCIe device, of course, but the SB600 contains only conventional PCI > devices with no visible PCIe port. > > Simplify and restructure only_one_child() so that we scan for all possible > devices below Root Ports as well as Switch Downstream Ports when > PCI_SCAN_ALL_PCIE_DEVS is set. > > This is enough to make Nemo work with "pci=pcie_scan_all". We would also > like to add a quirk to set PCI_SCAN_ALL_PCIE_DEVS automatically on Nemo so > users wouldn't have to use the "pci=pcie_scan_all" parameter, but we don't > have that yet. > > Link: https://lkml.kernel.org/r/CAErSpo55Q8Q=5p6_+uu7ahnw+53ibVDNRXxrzRV9QnUr_9EUfw@xxxxxxxxxxxxxx > Link: https://bugzilla.kernel.org/show_bug.cgi?id=198057 > Reported-and-Tested-by: Christian Zigotzky <chzigotzky@xxxxxxxxxxx> > Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> Applied to pci/enumeration for v4.16. > --- > drivers/pci/probe.c | 25 +++++++++++++++---------- > 1 file changed, 15 insertions(+), 10 deletions(-) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index 14e0ea1ff38b..303c0cb0550c 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -2215,22 +2215,27 @@ static unsigned next_fn(struct pci_bus *bus, struct pci_dev *dev, unsigned fn) > > static int only_one_child(struct pci_bus *bus) > { > - struct pci_dev *parent = bus->self; > + struct pci_dev *bridge = bus->self; > > - if (!parent || !pci_is_pcie(parent)) > + /* > + * Systems with unusual topologies set PCI_SCAN_ALL_PCIE_DEVS so > + * we scan for all possible devices, not just Device 0. > + */ > + if (pci_has_flag(PCI_SCAN_ALL_PCIE_DEVS)) > return 0; > - if (pci_pcie_type(parent) == PCI_EXP_TYPE_ROOT_PORT) > - return 1; > > /* > - * PCIe downstream ports are bridges that normally lead to only a > - * device 0, but if PCI_SCAN_ALL_PCIE_DEVS is set, scan all > - * possible devices, not just device 0. See PCIe spec r3.0, > - * sec 7.3.1. > + * A PCIe Downstream Port normally leads to a Link with only Device > + * 0 on it (PCIe spec r3.1, sec 7.3.1). As an optimization, scan > + * only for Device 0 in that situation. > + * > + * Checking has_secondary_link is a hack to identify Downstream > + * Ports because sometimes Switches are configured such that the > + * PCIe Port Type labels are backwards. > */ > - if (parent->has_secondary_link && > - !pci_has_flag(PCI_SCAN_ALL_PCIE_DEVS)) > + if (bridge && pci_is_pcie(bridge) && bridge->has_secondary_link) > return 1; > + > return 0; > } > >
