powerpc/smp: More generic support for "soft hotplug"

This adds more generic support for doing CPU hotplug with a simple
idle loop and no actual reset of the processors. The generic
smp_generic_kick_cpu() does the hotplug bringup trick if the PACA
shows that the CPU has already been started at boot and we provide
an accessor for the CPU state.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 25 insertions, 5 deletions

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 7bf2187dfd9..af7e7722eca 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -70,6 +70,10 @@
 static DEFINE_PER_CPU(struct task_struct *, idle_thread_array);
 #define get_idle_for_cpu(x)      (per_cpu(idle_thread_array, x))
 #define set_idle_for_cpu(x, p)   (per_cpu(idle_thread_array, x) = (p))
+
+/* State of each CPU during hotplug phases */
+static DEFINE_PER_CPU(int, cpu_state) = { 0 };
+
 #else
 static struct task_struct *idle_thread_array[NR_CPUS] __cpuinitdata ;
 #define get_idle_for_cpu(x)      (idle_thread_array[(x)])
@@ -104,12 +108,25 @@ int __devinit smp_generic_kick_cpu(int nr)
          * cpu_start field to become non-zero After we set cpu_start,
          * the processor will continue on to secondary_start
          */
-        paca[nr].cpu_start = 1;
-        smp_mb();
+        if (!paca[nr].cpu_start) {
+                paca[nr].cpu_start = 1;
+                smp_mb();
+                return 0;
+        }
+
+#ifdef CONFIG_HOTPLUG_CPU
+        /*
+         * 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;
+        smp_wmb();
+        smp_send_reschedule(nr);
+#endif /* CONFIG_HOTPLUG_CPU */
 
         return 0;
 }
-#endif
+#endif /* CONFIG_PPC64 */
 
 static irqreturn_t call_function_action(int irq, void *data)
 {
@@ -357,8 +374,6 @@ void __devinit smp_prepare_boot_cpu(void)
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
-/* State of each CPU during hotplug phases */
-static DEFINE_PER_CPU(int, cpu_state) = { 0 };
 
 int generic_cpu_disable(void)
 {
@@ -406,6 +421,11 @@ void generic_set_cpu_dead(unsigned int cpu)
 {
         per_cpu(cpu_state, cpu) = CPU_DEAD;
 }
+
+int generic_check_cpu_restart(unsigned int cpu)
+{
+        return per_cpu(cpu_state, cpu) == CPU_UP_PREPARE;
+}
 #endif
 
 struct create_idle {