PCI: Program MPS for RCiEP devices

Root Complex Integrated Endpoints (RCiEPs) do not have an upstream bridge,
so pci_configure_mps() previously ignored them, which may result in reduced
performance.

Instead, program the Max_Payload_Size of RCiEPs to the maximum supported
value (unless it is limited for the PCIE_BUS_PEER2PEER case).  This also
affects the subsequent programming of Max_Read_Request_Size because Linux
programs MRRS based on the MPS value.

Fixes: 9dae3a97 ("PCI: Move MPS configuration check to pci_configure_device()")
Link: https://lore.kernel.org/r/1585343775-4019-1-git-send-email-ashok.raj@intel.comTested-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org

drivers/pci/probe.c

@@ -1937,13 +1937,33 @@ static void pci_configure_mps(struct pci_dev *dev)
 	struct pci_dev *bridge = pci_upstream_bridge(dev);
 	int mps, mpss, p_mps, rc;
 
-	if (!pci_is_pcie(dev) || !bridge || !pci_is_pcie(bridge))
+	if (!pci_is_pcie(dev))
 		return;
 
 	/* MPS and MRRS fields are of type 'RsvdP' for VFs, short-circuit out */
 	if (dev->is_virtfn)
 		return;
 
+	/*
+	 * For Root Complex Integrated Endpoints, program the maximum
+	 * supported value unless limited by the PCIE_BUS_PEER2PEER case.
+	 */
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
+		if (pcie_bus_config == PCIE_BUS_PEER2PEER)
+			mps = 128;
+		else
+			mps = 128 << dev->pcie_mpss;
+		rc = pcie_set_mps(dev, mps);
+		if (rc) {
+			pci_warn(dev, "can't set Max Payload Size to %d; if necessary, use \"pci=pcie_bus_safe\" and report a bug\n",
+				 mps);
+		}
+		return;
+	}
+
+	if (!bridge || !pci_is_pcie(bridge))
+		return;
+
 	mps = pcie_get_mps(dev);
 	p_mps = pcie_get_mps(bridge);