powerpc/smp: add generic_set_cpu_up() to set cpu_state as CPU_UP_PREPARE

In the case of cpu hotplug, the cpu_state should be set to CPU_UP_PREPARE
when kicking cpu.  Otherwise, the cpu_state is always CPU_DEAD after
calling generic_set_cpu_dead(), which makes the delay in generic_cpu_die()
not happen.
Signed-off-by: Zhao Chenhui <chenhui.zhao@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/include/asm/smp.h

@@ -65,6 +65,7 @@ int generic_cpu_disable(void);
 void generic_cpu_die(unsigned int cpu);
 void generic_mach_cpu_die(void);
 void generic_set_cpu_dead(unsigned int cpu);
+void generic_set_cpu_up(unsigned int cpu);
 int generic_check_cpu_restart(unsigned int cpu);
 #endif
 

arch/powerpc/kernel/smp.c

@@ -102,7 +102,7 @@ int __devinit smp_generic_kick_cpu(int nr)
 	 * Ok it's not there, so it might be soft-unplugged, let's
 	 * try to bring it back
 	 */
-	per_cpu(cpu_state, nr) = CPU_UP_PREPARE;
+	generic_set_cpu_up(nr);
 	smp_wmb();
 	smp_send_reschedule(nr);
 #endif /* CONFIG_HOTPLUG_CPU */
@@ -413,6 +413,16 @@ void generic_set_cpu_dead(unsigned int cpu)
 	per_cpu(cpu_state, cpu) = CPU_DEAD;
 }
 
+/*
+ * The cpu_state should be set to CPU_UP_PREPARE in kick_cpu(), otherwise
+ * the cpu_state is always CPU_DEAD after calling generic_set_cpu_dead(),
+ * which makes the delay in generic_cpu_die() not happen.
+ */
+void generic_set_cpu_up(unsigned int cpu)
+{
+	per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
+}
+
 int generic_check_cpu_restart(unsigned int cpu)
 {
 	return per_cpu(cpu_state, cpu) == CPU_UP_PREPARE;