Can you try this? The link up check seemed unnecessary as it is racy.
What happens if the link goes down right after checking? That's the
only thing in the change that sticks out.

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c

b/drivers/pci/controller/dwc/pcie-designware-host.c
index 317ff512f8df..afee1a0e8883 100644

--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c

@@ -441,6 +441,9 @@ static void __iomem

*dw_pcie_other_conf_map_bus(struct pci_bus *bus,
        struct pcie_port *pp = bus->sysdata;
        struct dw_pcie *pci = to_dw_pcie_from_pp(pp);

+       if (!dw_pcie_link_up(pci))
+               return NULL;
+
        busdev = PCIE_ATU_BUS(bus->number) | 
PCIE_ATU_DEV(PCI_SLOT(devfn)) |
                 PCIE_ATU_FUNC(PCI_FUNC(devfn));