MIPS: Add arch generic CPU hotplug

Each platform has to add support for CPU hotplugging itself by providing
suitable definitions for the cpu_disable and cpu_die of the smp_ops
methods and setting SYS_SUPPORTS_HOTPLUG_CPU.  A platform should only set
SYS_SUPPORTS_HOTPLUG_CPU once all it's smp_ops definitions have the
necessary changes.  This patch contains the changes to the dummy smp_ops
definition for uni-processor systems.

Parts of the code contributed by Cavium Inc.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

7 files changed, 78 insertions, 7 deletions

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index b29f0280d712..eb7e8d795c6a 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -784,8 +784,17 @@ config SYS_HAS_EARLY_PRINTK
         bool
 
 config HOTPLUG_CPU
+        bool "Support for hot-pluggable CPUs"
+        depends on SMP && HOTPLUG && SYS_SUPPORTS_HOTPLUG_CPU
+        help
+          Say Y here to allow turning CPUs off and on. CPUs can be
+          controlled through /sys/devices/system/cpu.
+          (Note: power management support will enable this option
+            automatically on SMP systems. )
+          Say N if you want to disable CPU hotplug.
+
+config SYS_SUPPORTS_HOTPLUG_CPU
         bool
-        default n
 
 config I8259
         bool
diff --git a/arch/mips/include/asm/smp-ops.h b/arch/mips/include/asm/smp-ops.h
index 64ffc0290b84..fd545547b8aa 100644
--- a/arch/mips/include/asm/smp-ops.h
+++ b/arch/mips/include/asm/smp-ops.h
@@ -26,6 +26,10 @@ struct plat_smp_ops {
         void (*boot_secondary)(int cpu, struct task_struct *idle);
         void (*smp_setup)(void);
         void (*prepare_cpus)(unsigned int max_cpus);
+#ifdef CONFIG_HOTPLUG_CPU
+        int (*cpu_disable)(void);
+        void (*cpu_die)(unsigned int cpu);
+#endif
 };
 
 extern void register_smp_ops(struct plat_smp_ops *ops);
diff --git a/arch/mips/include/asm/smp.h b/arch/mips/include/asm/smp.h
index 2f83fa8631db..01f813dc3888 100644
--- a/arch/mips/include/asm/smp.h
+++ b/arch/mips/include/asm/smp.h
@@ -41,6 +41,7 @@ extern int __cpu_logical_map[NR_CPUS];
 /* Octeon - Tell another core to flush its icache */
 #define SMP_ICACHE_FLUSH        0x4
 
+extern cpumask_t cpu_callin_map;
 
 extern void asmlinkage smp_bootstrap(void);
 
@@ -56,6 +57,24 @@ static inline void smp_send_reschedule(int cpu)
         mp_ops->send_ipi_single(cpu, SMP_RESCHEDULE_YOURSELF);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static inline int __cpu_disable(void)
+{
+        extern struct plat_smp_ops *mp_ops;     /* private */
+
+        return mp_ops->cpu_disable();
+}
+
+static inline void __cpu_die(unsigned int cpu)
+{
+        extern struct plat_smp_ops *mp_ops;     /* private */
+
+        mp_ops->cpu_die(cpu);
+}
+
+extern void play_dead(void);
+#endif
+
 extern asmlinkage void smp_call_function_interrupt(void);
 
 extern void arch_send_call_function_single_ipi(int cpu);
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 1eaaa450e20c..c09d681b7181 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -50,10 +50,15 @@
  */
 void __noreturn cpu_idle(void)
 {
+        int cpu;
+
+        /* CPU is going idle. */
+        cpu = smp_processor_id();
+
         /* endless idle loop with no priority at all */
         while (1) {
                 tick_nohz_stop_sched_tick(1);
-                while (!need_resched()) {
+                while (!need_resched() && cpu_online(cpu)) {
 #ifdef CONFIG_MIPS_MT_SMTC
                         extern void smtc_idle_loop_hook(void);
 
@@ -62,6 +67,12 @@ void __noreturn cpu_idle(void)
                         if (cpu_wait)
                                 (*cpu_wait)();
                 }
+#ifdef CONFIG_HOTPLUG_CPU
+                if (!cpu_online(cpu) && !cpu_isset(cpu, cpu_callin_map) &&
+                    (system_state == SYSTEM_RUNNING ||
+                     system_state == SYSTEM_BOOTING))
+                        play_dead();
+#endif
                 tick_nohz_restart_sched_tick();
                 preempt_enable_no_resched();
                 schedule();
diff --git a/arch/mips/kernel/smp-up.c b/arch/mips/kernel/smp-up.c
index 878e3733bbb2..2508d55d68fd 100644
--- a/arch/mips/kernel/smp-up.c
+++ b/arch/mips/kernel/smp-up.c
@@ -55,6 +55,18 @@ static void __init up_prepare_cpus(unsigned int max_cpus)
 {
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static int up_cpu_disable(void)
+{
+        return -ENOSYS;
+}
+
+static void up_cpu_die(unsigned int cpu)
+{
+        BUG();
+}
+#endif
+
 struct plat_smp_ops up_smp_ops = {
         .send_ipi_single        = up_send_ipi_single,
         .send_ipi_mask          = up_send_ipi_mask,
@@ -64,4 +76,8 @@ struct plat_smp_ops up_smp_ops = {
         .boot_secondary         = up_boot_secondary,
         .smp_setup              = up_smp_setup,
         .prepare_cpus           = up_prepare_cpus,
+#ifdef CONFIG_HOTPLUG_CPU
+        .cpu_disable            = up_cpu_disable,
+        .cpu_die                = up_cpu_die,
+#endif
 };
diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 58f4679bbd43..bc7d9b05e2f4 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -45,7 +45,7 @@
 #include <asm/mipsmtregs.h>
 #endif /* CONFIG_MIPS_MT_SMTC */
 
-static volatile cpumask_t cpu_callin_map;       /* Bitmask of started secondaries */
+volatile cpumask_t cpu_callin_map;      /* Bitmask of started secondaries */
 int __cpu_number_map[NR_CPUS];          /* Map physical to logical */
 int __cpu_logical_map[NR_CPUS];         /* Map logical to physical */
 
@@ -201,6 +201,8 @@ void __devinit smp_prepare_boot_cpu(void)
  * and keep control until "cpu_online(cpu)" is set.  Note: cpu is
  * physical, not logical.
  */
+static struct task_struct *cpu_idle_thread[NR_CPUS];
+
 int __cpuinit __cpu_up(unsigned int cpu)
 {
         struct task_struct *idle;
@@ -210,9 +212,16 @@ int __cpuinit __cpu_up(unsigned int cpu)
          * The following code is purely to make sure
          * Linux can schedule processes on this slave.
          */
-        idle = fork_idle(cpu);
-        if (IS_ERR(idle))
-                panic(KERN_ERR "Fork failed for CPU %d", cpu);
+        if (!cpu_idle_thread[cpu]) {
+                idle = fork_idle(cpu);
+                cpu_idle_thread[cpu] = idle;
+
+                if (IS_ERR(idle))
+                        panic(KERN_ERR "Fork failed for CPU %d", cpu);
+        } else {
+                idle = cpu_idle_thread[cpu];
+                init_idle(idle, cpu);
+        }
 
         mp_ops->boot_secondary(cpu, idle);
 
diff --git a/arch/mips/kernel/topology.c b/arch/mips/kernel/topology.c
index 660e44ed44d7..cf3eb61fad12 100644
--- a/arch/mips/kernel/topology.c
+++ b/arch/mips/kernel/topology.c
@@ -17,7 +17,10 @@ static int __init topology_init(void)
 #endif /* CONFIG_NUMA */
 
         for_each_present_cpu(i) {
-                ret = register_cpu(&per_cpu(cpu_devices, i), i);
+                struct cpu *c = &per_cpu(cpu_devices, i);
+
+                c->hotpluggable = 1;
+                ret = register_cpu(c, i);
                 if (ret)
                         printk(KERN_WARNING "topology_init: register_cpu %d "
                                "failed (%d)\n", i, ret);