driver model: add support for CPUs.

- Create struct cpu to generically describe cpus (it simply contains
  a struct sys_device in it).

- Define an array of size NR_CPUS in arch/i386/kernel/cpu/common.c 
  and register each on bootup. This gives us something like:

# tree -d /sys/root/sys/
/sys/root/sys/
|-- cpu0
|-- pic0
`-- rtc0

and:

# tree -d /sys/bus/system/devices/
/sys/bus/system/devices/
|-- cpu0 -> ../../../root/sys/cpu0

- Define arch-specific CPU driver that's also registered on boot.
  That gives us: 

# tree -d /sys/bus/system/drivers/
/sys/bus/system/drivers/
|-- cpu

- Create a CPU device class that's registered very early. That 
  gives us all the CPUs in the system in one place:

# tree -d /sys/class/cpu/
/sys/class/cpu/
|-- devices
|   `-- 0 -> ../../../root/sys/cpu0
`-- drivers

Other archs are encouraged to do the same.

arch/i386/kernel/cpu/common.c

 #include <linux/init.h>
 #include <linux/string.h>
 #include <linux/delay.h>
+#include <linux/cpu.h>
 #include <linux/smp.h>
 #include <asm/semaphore.h>
 #include <asm/processor.h>
@@ -506,3 +507,37 @@ void __init cpu_init (void)
 	current->used_math = 0;
 	stts();
 }
+
+/*
+ * Bulk registration of the cpu devices with the system.
+ * Some of this stuff could possibly be moved into a shared 
+ * location..
+ * Also, these devices should be integrated with other CPU data..
+ */
+
+static struct cpu cpu_devices[NR_CPUS];
+
+static struct device_driver cpu_driver = {
+	.name		= "cpu",
+	.bus		= &system_bus_type,
+	.devclass	= &cpu_devclass,
+};
+
+static int __init register_cpus(void)
+{
+	int i;
+
+	driver_register(&cpu_driver);
+
+	for (i = 0; i < NR_CPUS; i++) {
+		struct sys_device * sysdev = &cpu_devices[i].sysdev;
+		sysdev->name = "cpu";
+		sysdev->id = i;
+		sysdev->dev.driver = &cpu_driver;
+		if (cpu_possible(i))
+			sys_device_register(sysdev);
+	}
+	return 0;
+}
+
+subsys_initcall(register_cpus);

drivers/base/Makefile

 # Makefile for the Linux device tree
 
 obj-y		:= core.o sys.o interface.o power.o bus.o \
-			driver.o class.o intf.o platform.o
+			driver.o class.o intf.o platform.o \
+			cpu.o
 
 obj-y		+= fs/
 
 export-objs	:= core.o power.o sys.o bus.o driver.o \
-			class.o intf.o
+			class.o intf.o cpu.o
 
 include $(TOPDIR)/Rules.make

drivers/base/cpu.c

+/*
+ * cpu.c - basic cpu class support
+ */
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/cpu.h>
+
+static int cpu_add_device(struct device * dev)
+{
+	return 0;
+}
+
+struct device_class cpu_devclass = {
+	.name		= "cpu",
+	.add_device	= cpu_add_device,
+};
+
+
+static int __init cpu_devclass_init(void)
+{
+	return devclass_register(&cpu_devclass);
+}
+
+postcore_initcall(cpu_devclass_init);
+
+EXPORT_SYMBOL(cpu_devclass);

include/linux/cpu.h

+/*
+ * cpu.h - generic cpu defition
+ *
+ * This is mainly for topological representation. We define the 
+ * basic 'struct cpu' here, which can be embedded in per-arch 
+ * definitions of processors.
+ *
+ * Basic handling of the devices is done in drivers/base/cpu.c
+ * and system devices are handled in drivers/base/sys.c. 
+ *
+ * CPUs are exported via driverfs in the class/cpu/devices/
+ * directory. 
+ *
+ * Per-cpu interfaces can be implemented using a struct device_interface. 
+ * See the following for how to do this: 
+ * - drivers/base/intf.c 
+ * - Documentation/driver-model/interface.txt
+ *
+ */
+
+#include <linux/device.h>
+
+extern struct device_class cpu_devclass;
+
+struct cpu {
+	struct sys_device sysdev;
+};
+