PCIe switch can be connected directly to the PCIe root complex in QEMU; ASPM does not expect this topology and dereferences NULL pointer when initializing. Downstream port can be also connected to the root complex without upstream one, so code checks for both, otherwise they dereference NULL on line drivers/pci/pcie/aspm.c:530 (alloc_pcie_link_state+13): parent = pdev->bus->parent->self->link_state; "pdev->bus->parent->self == NULL" if upstream port is connected directly to the root bus and "pdev->bus->parent == NULL" in the second case. v1 -> v2: (https://lkml.org/lkml/2013/6/19/753) - Initialization is aborted in pcie_aspm_init_link_state, where other special cases are being handled - pci_is_root_bus is used - Warning is printed Reproducer for "downstream -- root" and "downstream -- upstream -- root" (used qemu-kvm 1.5, q35 machine type might be missing on older ones) for parent in pcie.0 upstream; do qemu-kvm -m 128 -M q35 -nographic -no-reboot \ -device x3130-upstream,bus=pcie.0,id=upstream \ -device xio3130-downstream,bus=$parent,id=downstream,chassis=1 \ -device virtio-blk-pci,bus=downstream,id=virtio-zero,drive=zero \ -drive file=/dev/zero,id=zero,format=raw \ -kernel bzImage -append "console=ttyS0 panic=3" # pcie_aspm=off done ASPM in QEMU works if we connect upstream through root port -device ioh3420,bus=pcie.0,id=root.0 \ -device x3130-upstream,bus=root.0,id=upstream Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx> --- drivers/pci/pcie/aspm.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c index 403a443..209cd7f 100644 --- a/drivers/pci/pcie/aspm.c +++ b/drivers/pci/pcie/aspm.c @@ -570,6 +570,15 @@ void pcie_aspm_init_link_state(struct pci_dev *pdev) pdev->bus->self) return; + /* We require at least two ports between downstream and root bus */ + if (pci_pcie_type(pdev) == PCI_EXP_TYPE_DOWNSTREAM && + (pci_is_root_bus(pdev->bus) || + pci_is_root_bus(pdev->bus->parent))) { + dev_warn(&pdev->dev, "ASPM disabled" + " (connected directly to root bus)\n"); + return; + } + down_read(&pci_bus_sem); if (list_empty(&pdev->subordinate->devices)) goto out; -- 1.8.3.1 -- 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
