PCI: Set MPS to match upstream bridge

Firmware typically configures the PCIe fabric with a consistent Max Payload
Size setting based on the devices present at boot.  A hot-added device
typically has the power-on default MPS setting (128 bytes), which may not
match the fabric.

The previous Linux default, in the absence of any "pci=pcie_bus_*" options,
was PCIE_BUS_TUNE_OFF, in which we never touch MPS, even for hot-added
devices.

Add a new default setting, PCIE_BUS_DEFAULT, in which we make sure every
device's MPS setting matches the upstream bridge.  This makes it more
likely that a hot-added device will work in a system with optimized MPS
configuration.

Note that if we hot-add a device that only supports 128-byte MPS, it still
likely won't work because we don't reconfigure the rest of the fabric.
Booting with "pci=pcie_bus_peer2peer" is a workaround for this because it
sets MPS to 128 for everything.

[bhelgaas: changelog, new default, rework for pci_configure_device() path]
Tested-by: Keith Busch <keith.busch@intel.com>
Tested-by: Jordan Hargrave <jharg93@gmail.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>

drivers/pci/pci.c

@@ -81,7 +81,7 @@ unsigned long pci_cardbus_mem_size = DEFAULT_CARDBUS_MEM_SIZE;
 unsigned long pci_hotplug_io_size  = DEFAULT_HOTPLUG_IO_SIZE;
 unsigned long pci_hotplug_mem_size = DEFAULT_HOTPLUG_MEM_SIZE;
 
-enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_TUNE_OFF;
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_DEFAULT;
 
 /*
  * The default CLS is used if arch didn't set CLS explicitly and not

drivers/pci/probe.c

@@ -1278,7 +1278,7 @@ int pci_setup_device(struct pci_dev *dev)
 static void pci_configure_mps(struct pci_dev *dev)
 {
 	struct pci_dev *bridge = pci_upstream_bridge(dev);
-	int mps, p_mps;
+	int mps, p_mps, rc;
 
 	if (!pci_is_pcie(dev) || !bridge || !pci_is_pcie(bridge))
 		return;
@@ -1294,6 +1294,23 @@ static void pci_configure_mps(struct pci_dev *dev)
 			 mps, pci_name(bridge), p_mps);
 		return;
 	}
+
+	/*
+	 * Fancier MPS configuration is done later by
+	 * pcie_bus_configure_settings()
+	 */
+	if (pcie_bus_config != PCIE_BUS_DEFAULT)
+		return;
+
+	rc = pcie_set_mps(dev, p_mps);
+	if (rc) {
+		dev_warn(&dev->dev, "can't set Max Payload Size to %d; if necessary, use \"pci=pcie_bus_safe\" and report a bug\n",
+			 p_mps);
+		return;
+	}
+
+	dev_info(&dev->dev, "Max Payload Size set to %d (was %d, max %d)\n",
+		 p_mps, mps, 128 << dev->pcie_mpss);
 }
 
 static struct hpp_type0 pci_default_type0 = {
@@ -1821,7 +1838,8 @@ static int pcie_bus_configure_set(struct pci_dev *dev, void *data)
 	if (!pci_is_pcie(dev))
 		return 0;
 
-	if (pcie_bus_config == PCIE_BUS_TUNE_OFF)
+	if (pcie_bus_config == PCIE_BUS_TUNE_OFF ||
+	    pcie_bus_config == PCIE_BUS_DEFAULT)
 		return 0;
 
 	mps = 128 << *(u8 *)data;

drivers/pci/quirks.c

@@ -2862,7 +2862,8 @@ static void quirk_intel_mc_errata(struct pci_dev *dev)
 	int err;
 	u16 rcc;
 
-	if (pcie_bus_config == PCIE_BUS_TUNE_OFF)
+	if (pcie_bus_config == PCIE_BUS_TUNE_OFF ||
+	    pcie_bus_config == PCIE_BUS_DEFAULT)
 		return;
 
 	/* Intel errata specifies bits to change but does not say what they are.

include/linux/pci.h

@@ -738,10 +738,11 @@ struct pci_driver {
 void pcie_bus_configure_settings(struct pci_bus *bus);
 
 enum pcie_bus_config_types {
-	PCIE_BUS_TUNE_OFF,
-	PCIE_BUS_SAFE,
-	PCIE_BUS_PERFORMANCE,
-	PCIE_BUS_PEER2PEER,
+	PCIE_BUS_TUNE_OFF,	/* don't touch MPS at all */
+	PCIE_BUS_DEFAULT,	/* ensure MPS matches upstream bridge */
+	PCIE_BUS_SAFE,		/* use largest MPS boot-time devices support */
+	PCIE_BUS_PERFORMANCE,	/* use MPS and MRRS for best performance */
+	PCIE_BUS_PEER2PEER,	/* set MPS = 128 for all devices */
 };
 
 extern enum pcie_bus_config_types pcie_bus_config;