driver model: add support for multi-board systems.

- device struct sys_root for describing the individual boards of a multi-board
  system.

- allow for registration of alternate device roots.

- check if struct sys_device::root is set on registration, and add it as a child of
  an alternative root, if it's set. 

drivers/base/sys.c

@@ -23,6 +23,63 @@ static struct device system_bus = {
        .bus_id         = "sys",
 };
 
+
+/**
+ *	sys_register_root - add a subordinate system root
+ *	@root:	new root
+ *	
+ *	This is for NUMA-like systems so they can accurately 
+ *	represent the topology of the entire system.
+ *	As boards are discovered, a new struct sys_root should 
+ *	be allocated and registered. 
+ *	The discovery mechanism should initialize the id field
+ *	of the struture, as well as much of the embedded device
+ *	structure as possible, inlcuding the name, the bus_id
+ *	and parent fields.
+ *
+ *	This simply calls device_register on the embedded device.
+ *	On success, it will use the struct @root->sysdev 
+ *	device to create a pseudo-parent for system devices
+ *	on that board.
+ *
+ *	The platform code can then use @root to specifiy the
+ *	controlling board when discovering and registering 
+ *	system devices.
+ */
+int sys_register_root(struct sys_root * root)
+{
+	int error = 0;
+
+	if (!root)
+		return -EINVAL;
+
+	pr_debug("Registering system board %d\n",root->id);
+
+	error = device_register(&root->dev);
+	if (!error) {
+		strncpy(root->sysdev.bus_id,"sys",BUS_ID_SIZE);
+		strncpy(root->sysdev.name,"System Bus",DEVICE_NAME_SIZE);
+		root->sysdev.parent = &root->dev;
+		error = device_register(&root->sysdev);
+	};
+
+	return error;
+}
+
+/**
+ *	sys_unregister_root - remove subordinate root from tree
+ *	@root:	subordinate root in question.
+ *
+ *	We only decrement the reference count on @root->sysdev 
+ *	and @root->dev.
+ *	If both are 0, they will be cleaned up by the core.
+ */
+void sys_unegister_root(struct sys_root *  root)
+{
+	put_device(&root->sysdev);
+	put_device(&root->dev);
+}
+
 /**
  *	sys_device_register - add a system device to the tree
  *	@sysdev:	device in question
@@ -46,8 +103,12 @@ int sys_device_register(struct sys_device * sysdev)
 	if (!sysdev)
 		return -EINVAL;
 
-	if (!sysdev->dev.parent)
-		sysdev->dev.parent = &system_bus;
+	if (!sysdev->dev.parent) {
+		if (sysdev->root)
+			sysdev->dev.parent = &sysdev->root->sysdev;
+		else
+			sysdev->dev.parent = &system_bus;
+	}
 
 	/* make sure bus type is set */
 	if (!sysdev->dev.bus)

include/linux/device.h

@@ -379,6 +379,16 @@ extern void put_device(struct device * dev);
 
 /* drivers/base/sys.c */
 
+struct sys_root {
+	u32		id;
+	struct device 	dev;
+	struct device	sysdev;
+};
+
+extern int sys_register_root(struct sys_root *);
+extern void sys_unregister_root(struct sys_root *);
+
+
 struct sys_device {
 	char		* name;
 	u32		id;