PCI: PCIe: Introduce commad line switch for disabling port services

Introduce kernel command line switch pcie_ports= allowing one to
disable all of the native PCIe port services, so that PCIe ports
are treated like PCI-to-PCI bridges.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Documentation/kernel-parameters.txt

@@ -2042,6 +2042,10 @@ and is between 256 and 4096 characters. It is defined in the file
 		force	Enable ASPM even on devices that claim not to support it.
 			WARNING: Forcing ASPM on may cause system lockups.
 
+	pcie_ports=	[PCIE] PCIe ports handling:
+		compat	Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
+			ports driver.
+
 	pcie_pme=	[PCIE,PM] Native PCIe PME signaling options:
 			Format: {auto|force}[,nomsi]
 		auto	Use native PCIe PME signaling if the BIOS allows the

drivers/pci/pcie/portdrv.h

@@ -20,6 +20,8 @@
 
 #define get_descriptor_id(type, service) (((type - 4) << 4) | service)
 
+extern bool pcie_ports_disabled;
+
 extern struct bus_type pcie_port_bus_type;
 extern int pcie_port_device_register(struct pci_dev *dev);
 #ifdef CONFIG_PM

drivers/pci/pcie/portdrv_core.c

@@ -494,6 +494,9 @@ static void pcie_port_shutdown_service(struct device *dev) {}
  */
 int pcie_port_service_register(struct pcie_port_service_driver *new)
 {
+	if (pcie_ports_disabled)
+		return -ENODEV;
+
 	new->driver.name = (char *)new->name;
 	new->driver.bus = &pcie_port_bus_type;
 	new->driver.probe = pcie_port_probe_service;

drivers/pci/pcie/portdrv_pci.c

@@ -29,6 +29,18 @@ MODULE_AUTHOR(DRIVER_AUTHOR);
 MODULE_DESCRIPTION(DRIVER_DESC);
 MODULE_LICENSE("GPL");
 
+/* If this switch is set, PCIe port native services should not be enabled. */
+bool pcie_ports_disabled;
+
+static int __init pcie_port_setup(char *str)
+{
+	if (!strncmp(str, "compat", 6))
+		pcie_ports_disabled = true;
+
+	return 1;
+}
+__setup("pcie_ports=", pcie_port_setup);
+
 /* global data */
 
 static int pcie_portdrv_restore_config(struct pci_dev *dev)
@@ -301,6 +313,9 @@ static int __init pcie_portdrv_init(void)
 {
 	int retval;
 
+	if (pcie_ports_disabled)
+		return -EACCES;
+
 	dmi_check_system(pcie_portdrv_dmi_table);
 
 	retval = pcie_port_bus_register();