sh: CPU hotplug support.

This adds preliminary support for CPU hotplug for SH SMP systems.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/Kconfig

@@ -706,6 +706,13 @@ config NR_CPUS
 	  This is purely to save memory - each supported CPU adds
 	  approximately eight kilobytes to the kernel image.
 
+config HOTPLUG_CPU
+	bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
+	depends on SMP && HOTPLUG && EXPERIMENTAL
+	help
+	  Say Y here to experiment with turning CPUs off and on.  CPUs
+	  can be controlled through /sys/devices/system/cpu.
+
 source "kernel/Kconfig.preempt"
 
 config GUSA

arch/sh/include/asm/irq.h

 #ifndef __ASM_SH_IRQ_H
 #define __ASM_SH_IRQ_H
 
+#include <linux/cpumask.h>
 #include <asm/machvec.h>
 
 /*
@@ -50,6 +51,8 @@ static inline int generic_irq_demux(int irq)
 #define irq_demux(irq)		sh_mv.mv_irq_demux(irq)
 
 void init_IRQ(void);
+void migrate_irqs(void);
+
 asmlinkage int do_IRQ(unsigned int irq, struct pt_regs *regs);
 
 #ifdef CONFIG_IRQSTACKS

arch/sh/include/asm/smp-ops.h

@@ -7,20 +7,27 @@ struct plat_smp_ops {
 	void (*prepare_cpus)(unsigned int max_cpus);
 	void (*start_cpu)(unsigned int cpu, unsigned long entry_point);
 	void (*send_ipi)(unsigned int cpu, unsigned int message);
+	int (*cpu_disable)(unsigned int cpu);
+	void (*cpu_die)(unsigned int cpu);
+	void (*play_dead)(void);
 };
 
+extern struct plat_smp_ops *mp_ops;
 extern struct plat_smp_ops shx3_smp_ops;
 
 #ifdef CONFIG_SMP
 
 static inline void plat_smp_setup(void)
 {
-	extern struct plat_smp_ops *mp_ops;	/* private */
-
 	BUG_ON(!mp_ops);
 	mp_ops->smp_setup();
 }
 
+static inline void play_dead(void)
+{
+	mp_ops->play_dead();
+}
+
 extern void register_smp_ops(struct plat_smp_ops *ops);
 
 #else
@@ -34,6 +41,11 @@ static inline void register_smp_ops(struct plat_smp_ops *ops)
 {
 }
 
+static inline void play_dead(void)
+{
+	BUG();
+}
+
 #endif /* CONFIG_SMP */
 
 #endif /* __ASM_SH_SMP_OPS_H */

arch/sh/include/asm/smp.h

@@ -38,9 +38,26 @@ void smp_timer_broadcast(const struct cpumask *mask);
 
 void local_timer_interrupt(void);
 void local_timer_setup(unsigned int cpu);
+void local_timer_stop(unsigned int cpu);
 
 void arch_send_call_function_single_ipi(int cpu);
-extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);
+void arch_send_call_function_ipi_mask(const struct cpumask *mask);
+
+void native_play_dead(void);
+void native_cpu_die(unsigned int cpu);
+int native_cpu_disable(unsigned int cpu);
+
+#ifdef CONFIG_HOTPLUG_CPU
+void play_dead_common(void);
+extern int __cpu_disable(void);
+
+static inline void __cpu_die(unsigned int cpu)
+{
+	extern struct plat_smp_ops *mp_ops;     /* private */
+
+	mp_ops->cpu_die(cpu);
+}
+#endif
 
 static inline int hard_smp_processor_id(void)
 {

arch/sh/kernel/idle.c

@@ -19,6 +19,7 @@
 #include <asm/pgalloc.h>
 #include <asm/system.h>
 #include <asm/atomic.h>
+#include <asm/smp.h>
 
 void (*pm_idle)(void) = NULL;
 
@@ -89,10 +90,13 @@ void cpu_idle(void)
 	while (1) {
 		tick_nohz_stop_sched_tick(1);
 
-		while (!need_resched() && cpu_online(cpu)) {
+		while (!need_resched()) {
 			check_pgt_cache();
 			rmb();
 
+			if (cpu_is_offline(cpu))
+				play_dead();
+
 			local_irq_disable();
 			/* Don't trace irqs off for idle */
 			stop_critical_timings();

arch/sh/kernel/irq.c

@@ -12,6 +12,7 @@
 #include <linux/kernel_stat.h>
 #include <linux/seq_file.h>
 #include <linux/ftrace.h>
+#include <linux/delay.h>
 #include <asm/processor.h>
 #include <asm/machvec.h>
 #include <asm/uaccess.h>
@@ -292,3 +293,44 @@ int __init arch_probe_nr_irqs(void)
 	return 0;
 }
 #endif
+
+#ifdef CONFIG_HOTPLUG_CPU
+static void route_irq(struct irq_desc *desc, unsigned int irq, unsigned int cpu)
+{
+	printk(KERN_INFO "IRQ%u: moving from cpu%u to cpu%u\n",
+	       irq, desc->node, cpu);
+
+	raw_spin_lock_irq(&desc->lock);
+	desc->chip->set_affinity(irq, cpumask_of(cpu));
+	raw_spin_unlock_irq(&desc->lock);
+}
+
+/*
+ * The CPU has been marked offline.  Migrate IRQs off this CPU.  If
+ * the affinity settings do not allow other CPUs, force them onto any
+ * available CPU.
+ */
+void migrate_irqs(void)
+{
+	struct irq_desc *desc;
+	unsigned int irq, cpu = smp_processor_id();
+
+	for_each_irq_desc(irq, desc) {
+		if (desc->node == cpu) {
+			unsigned int newcpu = cpumask_any_and(desc->affinity,
+							      cpu_online_mask);
+			if (newcpu >= nr_cpu_ids) {
+				if (printk_ratelimit())
+					printk(KERN_INFO "IRQ%u no longer affine to CPU%u\n",
+					       irq, cpu);
+
+				cpumask_setall(desc->affinity);
+				newcpu = cpumask_any_and(desc->affinity,
+							 cpu_online_mask);
+			}
+
+			route_irq(desc, irq, newcpu);
+		}
+	}
+}
+#endif

arch/sh/kernel/localtimer.c

@@ -60,3 +60,7 @@ void local_timer_setup(unsigned int cpu)
 
 	clockevents_register_device(clk);
 }
+
+void local_timer_stop(unsigned int cpu)
+{
+}

arch/sh/kernel/smp.c

@@ -79,6 +79,105 @@ void __init smp_prepare_boot_cpu(void)
 	per_cpu(cpu_state, cpu) = CPU_ONLINE;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+void native_cpu_die(unsigned int cpu)
+{
+	unsigned int i;
+
+	for (i = 0; i < 10; i++) {
+		smp_rmb();
+		if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
+			if (system_state == SYSTEM_RUNNING)
+				pr_info("CPU %u is now offline\n", cpu);
+
+			return;
+		}
+
+		msleep(100);
+	}
+
+	pr_err("CPU %u didn't die...\n", cpu);
+}
+
+int native_cpu_disable(unsigned int cpu)
+{
+	return cpu == 0 ? -EPERM : 0;
+}
+
+void play_dead_common(void)
+{
+	idle_task_exit();
+	irq_ctx_exit(raw_smp_processor_id());
+	mb();
+
+	__get_cpu_var(cpu_state) = CPU_DEAD;
+	local_irq_disable();
+}
+
+void native_play_dead(void)
+{
+	play_dead_common();
+}
+
+int __cpu_disable(void)
+{
+	unsigned int cpu = smp_processor_id();
+	struct task_struct *p;
+	int ret;
+
+	ret = mp_ops->cpu_disable(cpu);
+	if (ret)
+		return ret;
+
+	/*
+	 * Take this CPU offline.  Once we clear this, we can't return,
+	 * and we must not schedule until we're ready to give up the cpu.
+	 */
+	set_cpu_online(cpu, false);
+
+	/*
+	 * OK - migrate IRQs away from this CPU
+	 */
+	migrate_irqs();
+
+	/*
+	 * Stop the local timer for this CPU.
+	 */
+	local_timer_stop(cpu);
+
+	/*
+	 * Flush user cache and TLB mappings, and then remove this CPU
+	 * from the vm mask set of all processes.
+	 */
+	flush_cache_all();
+	local_flush_tlb_all();
+
+	read_lock(&tasklist_lock);
+	for_each_process(p)
+		if (p->mm)
+			cpumask_clear_cpu(cpu, mm_cpumask(p->mm));
+	read_unlock(&tasklist_lock);
+
+	return 0;
+}
+#else /* ... !CONFIG_HOTPLUG_CPU */
+int native_cpu_disable(void)
+{
+	return -ENOSYS;
+}
+
+void native_cpu_die(unsigned int cpu)
+{
+	/* We said "no" in __cpu_disable */
+	BUG();
+}
+
+void native_play_dead(void)
+{
+	BUG();
+}
+#endif
+
 asmlinkage void __cpuinit start_secondary(void)
 {
 	unsigned int cpu = smp_processor_id();
@@ -88,8 +187,8 @@ asmlinkage void __cpuinit start_secondary(void)
 	atomic_inc(&mm->mm_count);
 	atomic_inc(&mm->mm_users);
 	current->active_mm = mm;
-	BUG_ON(current->mm);
 	enter_lazy_tlb(mm, current);
+	local_flush_tlb_all();
 
 	per_cpu_trap_init();
 
@@ -156,6 +255,7 @@ int __cpuinit __cpu_up(unsigned int cpu)
 			break;
 
 		udelay(10);
+		barrier();
 	}
 
 	if (cpu_online(cpu))
@@ -270,7 +370,6 @@ static void flush_tlb_mm_ipi(void *mm)
  * behalf of debugees, kswapd stealing pages from another process etc).
  * Kanoj 07/00.
  */
-
 void flush_tlb_mm(struct mm_struct *mm)
 {
 	preempt_disable();