[PATCH] make smp_prepare_cpu to a weak function

I really wish smp_prepare_cpu() would disappear eventually. In the interim
this is ideally a weak function, so we dont end up changing several places
to define this dummy in headers.

Today since the dummy declaration is done only in drivers/base/cpu.c but
the function is called in kernel/power/smp.c i get undefined reference in
my cpu hotplug code for x86_64 under development.

Signed-off-by: Ashok Raj <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/base/cpu.c

···
 EXPORT_SYMBOL(cpu_sysdev_class);
 
 #ifdef CONFIG_HOTPLUG_CPU
-#ifndef __HAVE_ARCH_SMP_PREPARE_CPU
-#define smp_prepare_cpu(cpu) (0)
-#endif
+int __attribute__((weak)) smp_prepare_cpu (int cpu)
+{
+	return 0;
+}
 
 static ssize_t show_online(struct sys_device *dev, char *buf)
 {
···
 		break;
 	case '1':
 		ret = smp_prepare_cpu(cpu->sysdev.id);
-		if (ret == 0)
+		if (!ret)
 			ret = cpu_up(cpu->sysdev.id);
 		break;
 	default:

include/asm-i386/smp.h

···
 #ifdef CONFIG_HOTPLUG_CPU
 extern void cpu_exit_clear(void);
 extern void cpu_uninit(void);
-
-#define __HAVE_ARCH_SMP_PREPARE_CPU
-extern int smp_prepare_cpu(int cpu);
 #endif
 
 /*

include/linux/cpu.h

···
 	register_cpu_notifier(&fn##_nb);			\
 }
 int cpu_down(unsigned int cpu);
+extern int __attribute__((weak)) smp_prepare_cpu(int cpu);
 #define cpu_is_offline(cpu) unlikely(!cpu_online(cpu))
 #else
 #define lock_cpu_hotplug()	do { } while (0)