diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index b9d6c37272dd..9b4c21692081 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -6282,6 +6282,58 @@ DECLARE_PCI_FIXUP_ENABLE(PCI_VENDOR_ID_PERICOM, 0xb404,
 DECLARE_PCI_FIXUP_RESUME(PCI_VENDOR_ID_PERICOM, 0xb404,
 			 pci_fixup_pericom_acs_store_forward);
 
+/*
+ * Some Pericom/Diodes PI7C9X3G606GPC switches require downstream Port 4
+ * BAR 0 to mirror BAR 0 of the immediate upstream port.  Firmware may
+ * program this during boot, but Linux resource assignment can move the
+ * upstream BAR.
+ *
+ * Diodes confirmed Tile0/P4 appears to Linux as device 4, function 0 on
+ * the bus below the upstream port.  Match that downstream function and
+ * re-apply the mirror after resource assignment and early resume.
+ */
+static void pci_fixup_pericom_pi7c9x3g606gpc_bar0_mirror(struct pci_dev *pdev)
+{
+	struct pci_dev *upstream;
+	u32 bar, upstream_bar;
+
+	if (pci_pcie_type(pdev) != PCI_EXP_TYPE_DOWNSTREAM)
+		return;
+
+	if (PCI_SLOT(pdev->devfn) != 4 || PCI_FUNC(pdev->devfn))
+		return;
+
+	upstream = pci_upstream_bridge(pdev);
+	if (!upstream || upstream->vendor != PCI_VENDOR_ID_PERICOM ||
+	    upstream->device != PCI_DEVICE_ID_PERICOM_PI7C9X3G606GPC ||
+	    pci_pcie_type(upstream) != PCI_EXP_TYPE_UPSTREAM)
+		return;
+
+	pci_read_config_dword(upstream, PCI_BASE_ADDRESS_0, &upstream_bar);
+	if (upstream_bar & PCI_BASE_ADDRESS_SPACE_IO)
+		return;
+
+	if (!(upstream_bar & PCI_BASE_ADDRESS_MEM_MASK)) {
+		pci_warn(pdev, "skipping PI7C9X3G606GPC BAR0 mirror workaround because upstream BAR 0 is unassigned\n");
+		return;
+	}
+
+	pci_read_config_dword(pdev, PCI_BASE_ADDRESS_0, &bar);
+	if (bar == upstream_bar)
+		return;
+
+	/* Port 4 BAR 0 may read back as zero even after a successful write. */
+	pci_write_config_dword(pdev, PCI_BASE_ADDRESS_0, upstream_bar);
+	pci_info(pdev, "wrote upstream BAR 0 %#x to Port 4 BAR 0 for PI7C9X3G606GPC BAR0 mirror workaround\n",
+		 upstream_bar);
+}
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_PERICOM,
+			PCI_DEVICE_ID_PERICOM_PI7C9X3G606GPC,
+			pci_fixup_pericom_pi7c9x3g606gpc_bar0_mirror);
+DECLARE_PCI_FIXUP_RESUME_EARLY(PCI_VENDOR_ID_PERICOM,
+			       PCI_DEVICE_ID_PERICOM_PI7C9X3G606GPC,
+			       pci_fixup_pericom_pi7c9x3g606gpc_bar0_mirror);
+
 static void nvidia_ion_ahci_fixup(struct pci_dev *pdev)
 {
 	pdev->dev_flags |= PCI_DEV_FLAGS_HAS_MSI_MASKING;
diff --git a/include/linux/pci_ids.h b/include/linux/pci_ids.h
index 406abf629be2..e0c23a161305 100644
--- a/include/linux/pci_ids.h
+++ b/include/linux/pci_ids.h
@@ -1845,6 +1845,7 @@
 #define PCI_DEVICE_ID_NVIDIA_SGS_RIVA128 0x0018
 
 #define PCI_VENDOR_ID_PERICOM			0x12D8
+#define PCI_DEVICE_ID_PERICOM_PI7C9X3G606GPC	0xc008
 #define PCI_DEVICE_ID_PERICOM_PI7C9X7951	0x7951
 #define PCI_DEVICE_ID_PERICOM_PI7C9X7952	0x7952
 #define PCI_DEVICE_ID_PERICOM_PI7C9X7954	0x7954