pci: skip unnecessary PCIe scanning

Use the same mechanism as the Linux kernel to skip unnecessary (and in
the case of the J722S, errant) scanning of direct children of root
ports, downstream ports or bridges.

Based on Linux PCI code in the following files as of b927546677c8:
  drivers/pci/probe.c
  drivers/pci/pci.h
  include/linux/pci.h

Signed-off-by: George McCollister <[email protected]>
Tested-by: Bryan Brattlof <[email protected]>

1 files changed, 35 insertions, 0 deletions

diff --git a/drivers/pci/pci-uclass.c b/drivers/pci/pci-uclass.c
index c370f8c6400..83b76d01f24 100644
--- a/drivers/pci/pci-uclass.c
+++ b/drivers/pci/pci-uclass.c
@@ -872,6 +872,38 @@ __weak extern void board_pci_fixup_dev(struct udevice *bus, struct udevice *dev)
 {
 }
 
+static int only_one_child(struct udevice *bus)
+{
+	int pos;
+
+	if (!dev_get_parent_plat(bus))
+		return 0;
+
+	/*
+	 * 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.
+	 */
+	pos = dm_pci_find_capability(bus, PCI_CAP_ID_EXP);
+	if (pos) {
+		ulong reg;
+		ulong pcie_type;
+
+		dm_pci_read_config(bus, pos + PCI_EXP_FLAGS,
+				   &reg, PCI_SIZE_16);
+
+		pcie_type = (reg & PCI_EXP_FLAGS_TYPE) >> 4;
+
+		if (pcie_type == PCI_EXP_TYPE_ROOT_PORT ||
+		    pcie_type == PCI_EXP_TYPE_DOWNSTREAM ||
+		    pcie_type == PCI_EXP_TYPE_PCIE_BRIDGE) {
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
 int pci_bind_bus_devices(struct udevice *bus)
 {
 	ulong vendor, device;
@@ -895,6 +927,9 @@ int pci_bind_bus_devices(struct udevice *bus)
 		if (PCI_FUNC(bdf) && !found_multi)
 			continue;
 
+		if (only_one_child(bus) && (PCI_MASK_BUS(bdf) > 0))
+			continue;
+
 		/* Check only the first access, we don't expect problems */
 		ret = pci_bus_read_config(bus, bdf, PCI_VENDOR_ID, &vendor,
 					  PCI_SIZE_16);