PCI: enable driver multi-threaded probe

This provides a build and run-time option to turn on multhreaded probe
for all PCI drivers.  It can cause bad problems on multi-processor
machines that take a while to find their root disks, and play havoc on
machines that don't use persistant device names for block or network
devices.

But it can cause speedups on some machines, my tiny laptop's boot goes
up by 0.4 seconds, and my desktop boots up several seconds faster.

Use at your own risk!!!
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/pci/Kconfig

@@ -17,6 +17,31 @@ config PCI_MSI
 
 	   If you don't know what to do here, say N.
 
+config PCI_MULTITHREAD_PROBE
+	bool "PCI Multi-threaded probe (EXPERIMENTAL)"
+	depends on PCI && EXPERIMENTAL
+	help
+	  Say Y here if you want the PCI core to spawn a new thread for
+	  every PCI device that is probed.  This can cause a huge
+	  speedup in boot times on multiprocessor machines, and even a
+	  smaller speedup on single processor machines.
+
+	  But it can also cause lots of bad things to happen.  A number
+	  of PCI drivers can not properly handle running in this way,
+	  some will just not work properly at all, while others might
+	  decide to blow up power supplies with a huge load all at once,
+	  so use this option at your own risk.
+
+	  It is very unwise to use this option if you are not using a
+	  boot process that can handle devices being created in any
+	  order.  A program that can create persistant block and network
+	  device names (like udev) is a good idea if you wish to use
+	  this option.
+
+	  Again, use this option at your own risk, you have been warned!
+
+	  When in doubt, say N.
+
 config PCI_DEBUG
 	bool "PCI Debugging"
 	depends on PCI && DEBUG_KERNEL

drivers/pci/pci-driver.c

@@ -17,6 +17,16 @@
  *  Registration of PCI drivers and handling of hot-pluggable devices.
  */
 
+/* multithreaded probe logic */
+static int pci_multithread_probe =
+#ifdef CONFIG_PCI_MULTITHREAD_PROBE
+	1;
+#else
+	0;
+#endif
+__module_param_call("", pci_multithread_probe, param_set_bool, param_get_bool, &pci_multithread_probe, 0644);
+
+
 /*
  * Dynamic device IDs are disabled for !CONFIG_HOTPLUG
  */
@@ -408,6 +418,7 @@ int __pci_register_driver(struct pci_driver *drv, struct module *owner)
 	drv->driver.bus = &pci_bus_type;
 	drv->driver.owner = owner;
 	drv->driver.kobj.ktype = &pci_driver_kobj_type;
+	drv->driver.multithread_probe = pci_multithread_probe;
 
 	spin_lock_init(&drv->dynids.lock);
 	INIT_LIST_HEAD(&drv->dynids.list);