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>

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

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);

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);

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();

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
 };

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);
 

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);