PCI: Disable MPS configuration by default

Add the ability to disable PCI-E MPS turning and using the BIOS
configured MPS defaults. Due to the number of issues recently
discovered on some x86 chipsets, make this the default behavior.

Also, add the option for peer to peer DMA MPS configuration. Peer to
peer DMA is outside the scope of this patch, but MPS configuration could
prevent it from working by having the MPS on one root port different
than the MPS on another. To work around this, simply make the system
wide MPS the smallest possible value (128B).

Signed-off-by: Jon Mason <[e-mail]>
Acked-by: Benjamin Herrenschmidt <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/pci/pci.c

···
 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_SAFE;
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_TUNE_OFF;
 
 /*
  * The default CLS is used if arch didn't set CLS explicitly and not
···
 				pci_hotplug_io_size = memparse(str + 9, &str);
 			} else if (!strncmp(str, "hpmemsize=", 10)) {
 				pci_hotplug_mem_size = memparse(str + 10, &str);
+			} else if (!strncmp(str, "pcie_bus_tune_off", 17)) {
+				pcie_bus_config = PCIE_BUS_TUNE_OFF;
 			} else if (!strncmp(str, "pcie_bus_safe", 13)) {
 				pcie_bus_config = PCIE_BUS_SAFE;
 			} else if (!strncmp(str, "pcie_bus_perf", 13)) {
 				pcie_bus_config = PCIE_BUS_PERFORMANCE;
+			} else if (!strncmp(str, "pcie_bus_peer2peer", 18)) {
+				pcie_bus_config = PCIE_BUS_PEER2PEER;
 			} else {
 				printk(KERN_ERR "PCI: Unknown option `%s'\n",
 						str);

drivers/pci/probe.c

···
  */
 void pcie_bus_configure_settings(struct pci_bus *bus, u8 mpss)
 {
-	u8 smpss = mpss;
+	u8 smpss;
 
 	if (!pci_is_pcie(bus->self))
 		return;
 
+	if (pcie_bus_config == PCIE_BUS_TUNE_OFF)
+		return;
+
+	/* FIXME - Peer to peer DMA is possible, though the endpoint would need
+	 * to be aware to the MPS of the destination.  To work around this,
+	 * simply force the MPS of the entire system to the smallest possible.
+	 */
+	if (pcie_bus_config == PCIE_BUS_PEER2PEER)
+		smpss = 0;
+
 	if (pcie_bus_config == PCIE_BUS_SAFE) {
+		smpss = mpss;
+
 		pcie_find_smpss(bus->self, &smpss);
 		pci_walk_bus(bus, pcie_find_smpss, &smpss);
 	}

include/linux/pci.h

···
 extern void pcie_bus_configure_settings(struct pci_bus *bus, u8 smpss);
 
 enum pcie_bus_config_types {
-	PCIE_BUS_PERFORMANCE,
+	PCIE_BUS_TUNE_OFF,
 	PCIE_BUS_SAFE,
+	PCIE_BUS_PERFORMANCE,
 	PCIE_BUS_PEER2PEER,
 };