--- include/linux/pci.h.orig	2018-03-26 16:51:18.050000000 +0000
+++ include/linux/pci.h	2018-04-30 18:29:14.140000000 +0000
@@ -193,6 +193,7 @@
 enum pci_bus_flags {
 	PCI_BUS_FLAGS_NO_MSI   = (__force pci_bus_flags_t) 1,
 	PCI_BUS_FLAGS_NO_MMRBC = (__force pci_bus_flags_t) 2,
+	PCI_BUS_FLAGS_NO_EXTCFG = (__force pci_bus_flags_t) 4,
 };
 
 /* These values come from the PCI Express Spec */
--- drivers/pci/probe.c.orig	2018-01-22 09:29:52.000000000 +0000
+++ drivers/pci/probe.c	2018-05-02 13:44:35.530000000 +0000
@@ -664,6 +664,23 @@
 	}
 }
 
+static bool pci_bridge_child_bus_ext_cfg_accessible(struct pci_dev *bridge)
+{
+	int pos;
+	u32 status;
+
+	if (!pci_is_pcie(bridge) || /* PCI/PCI bridge */
+	    (pci_pcie_type(bridge) == PCI_EXP_TYPE_PCIE_BRIDGE) || /* PCIe/PCI bridge in forward mode */
+	    (pci_pcie_type(bridge) == PCI_EXP_TYPE_PCI_BRIDGE)) {  /* PCIe/PCI bridge in reverse mode */
+		pos = pci_find_capability(bridge, PCI_CAP_ID_PCIX);
+		if (pos)
+			pci_read_config_dword(bridge, pos + PCI_X_STATUS, &status);
+		return pos && (status & (PCI_X_STATUS_266MHZ | PCI_X_STATUS_533MHZ));
+	}
+
+	return true;
+}
+
 static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
 					   struct pci_dev *bridge, int busnr)
 {
@@ -725,6 +742,19 @@
 	/* Create legacy_io and legacy_mem files for this bus */
 	pci_create_legacy_files(child);
 
+	/*
+	 * if bus_flags inherited from parent bus do not already report lack of extended config
+	 * space support, check if supported by child bus by checking its parent bridge
+	 */
+	if (bridge && !(child->bus_flags & PCI_BUS_FLAGS_NO_EXTCFG)) {
+		if (!pci_bridge_child_bus_ext_cfg_accessible(bridge)) {
+			child->bus_flags |= PCI_BUS_FLAGS_NO_EXTCFG;
+			dev_info(&child->dev, "extended config space not accessible due to parent bridge\n");
+		}
+	} else {
+		dev_info(&child->dev, "extended config space not accessible due to parent bus\n");
+	}
+
 	return child;
 }
 
@@ -1084,6 +1114,9 @@
 	u32 status;
 	u16 class;
 
+	if (dev->bus->bus_flags & PCI_BUS_FLAGS_NO_EXTCFG)
+		return PCI_CFG_SPACE_SIZE;
+
 	class = dev->class >> 8;
 	if (class == PCI_CLASS_BRIDGE_HOST)
 		return pci_cfg_space_size_ext(dev);