commit 75eaf674066590e79b3e03d32488871fc881ab40
Author: Bjorn Helgaas <bhelgaas@google.com>
Date:   Thu Nov 30 15:22:39 2017 -0600

    PCI: Make PCI_SCAN_ALL_PCIE_DEVS work for Root Ports as well as Downstream
    
    Previously PCI_SCAN_ALL_PCIE_DEVS (set by quirks or the "pci=pcie_scan_all"
    kernel parameter) only affected Switch Downstream Ports, not Root Ports.
    
    Simplify and restructure only_one_child() so PCI_SCAN_ALL_PCIE_DEVS means
    we scan for all possible devices below Root Ports as well as Switch
    Downstream Ports.
    
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 14e0ea1ff38b..9e57d4ef0c1f 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2217,20 +2217,28 @@ static int only_one_child(struct pci_bus *bus)
 {
 	struct pci_dev *parent = bus->self;
 
-	if (!parent || !pci_is_pcie(parent))
+	if (!parent)
+		return 0;
+
+	/*
+	 * 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 (pci_is_pcie(parent) && parent->has_secondary_link)
 		return 1;
+
 	return 0;
 }