[ARM SMP] Add hotplug CPU infrastructure
This patch adds the infrastructure to support hotplug CPU on ARM
platforms.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index dc6d834..6b12d71 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -349,6 +349,13 @@
depends on SMP
default "4"
+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.
+
config PREEMPT
bool "Preemptible Kernel (EXPERIMENTAL)"
depends on EXPERIMENTAL
diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 3284118..9def440 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -1050,3 +1050,34 @@
}
__setup("noirqdebug", noirqdebug_setup);
+
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * 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)
+{
+ unsigned int i, cpu = smp_processor_id();
+
+ for (i = 0; i < NR_IRQS; i++) {
+ struct irqdesc *desc = irq_desc + i;
+
+ if (desc->cpu == cpu) {
+ unsigned int newcpu = any_online_cpu(desc->affinity);
+
+ if (newcpu == NR_CPUS) {
+ if (printk_ratelimit())
+ printk(KERN_INFO "IRQ%u no longer affine to CPU%u\n",
+ i, cpu);
+
+ cpus_setall(desc->affinity);
+ newcpu = any_online_cpu(desc->affinity);
+ }
+
+ route_irq(desc, i, newcpu);
+ }
+ }
+}
+#endif /* CONFIG_HOTPLUG_CPU */
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 409db6d..ba29827 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -26,6 +26,7 @@
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/init.h>
+#include <linux/cpu.h>
#include <asm/system.h>
#include <asm/io.h>
@@ -105,6 +106,14 @@
/* endless idle loop with no priority at all */
while (1) {
void (*idle)(void) = pm_idle;
+
+#ifdef CONFIG_HOTPLUG_CPU
+ if (cpu_is_offline(smp_processor_id())) {
+ leds_event(led_idle_start);
+ cpu_die();
+ }
+#endif
+
if (!idle)
idle = default_idle;
preempt_disable();
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index b40915d..edb5a40 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -159,6 +159,91 @@
return ret;
}
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * __cpu_disable runs on the processor to be shutdown.
+ */
+int __cpuexit __cpu_disable(void)
+{
+ unsigned int cpu = smp_processor_id();
+ struct task_struct *p;
+ int ret;
+
+ ret = mach_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.
+ */
+ cpu_clear(cpu, cpu_online_map);
+
+ /*
+ * OK - migrate IRQs away from this CPU
+ */
+ migrate_irqs();
+
+ /*
+ * 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)
+ cpu_clear(cpu, p->mm->cpu_vm_mask);
+ }
+ read_unlock(&tasklist_lock);
+
+ return 0;
+}
+
+/*
+ * called on the thread which is asking for a CPU to be shutdown -
+ * waits until shutdown has completed, or it is timed out.
+ */
+void __cpuexit __cpu_die(unsigned int cpu)
+{
+ if (!platform_cpu_kill(cpu))
+ printk("CPU%u: unable to kill\n", cpu);
+}
+
+/*
+ * Called from the idle thread for the CPU which has been shutdown.
+ *
+ * Note that we disable IRQs here, but do not re-enable them
+ * before returning to the caller. This is also the behaviour
+ * of the other hotplug-cpu capable cores, so presumably coming
+ * out of idle fixes this.
+ */
+void __cpuexit cpu_die(void)
+{
+ unsigned int cpu = smp_processor_id();
+
+ local_irq_disable();
+ idle_task_exit();
+
+ /*
+ * actual CPU shutdown procedure is at least platform (if not
+ * CPU) specific
+ */
+ platform_cpu_die(cpu);
+
+ /*
+ * Do not return to the idle loop - jump back to the secondary
+ * cpu initialisation. There's some initialisation which needs
+ * to be repeated to undo the effects of taking the CPU offline.
+ */
+ __asm__("mov sp, %0\n"
+ " b secondary_start_kernel"
+ :
+ : "r" ((void *)current->thread_info + THREAD_SIZE - 8));
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
/*
* This is the secondary CPU boot entry. We're using this CPUs
* idle thread stack, but a set of temporary page tables.
diff --git a/include/asm-arm/irq.h b/include/asm-arm/irq.h
index f97912f..59975ee 100644
--- a/include/asm-arm/irq.h
+++ b/include/asm-arm/irq.h
@@ -47,5 +47,6 @@
struct pt_regs;
int handle_IRQ_event(unsigned int, struct pt_regs *, struct irqaction *);
+extern void migrate_irqs(void);
#endif
diff --git a/include/asm-arm/smp.h b/include/asm-arm/smp.h
index dbb4d85..551cd3c 100644
--- a/include/asm-arm/smp.h
+++ b/include/asm-arm/smp.h
@@ -66,4 +66,14 @@
};
extern struct secondary_data secondary_data;
+extern int __cpu_disable(void);
+extern int mach_cpu_disable(unsigned int cpu);
+
+extern void __cpu_die(unsigned int cpu);
+extern void cpu_die(void);
+
+extern void platform_cpu_die(unsigned int cpu);
+extern int platform_cpu_kill(unsigned int cpu);
+extern void platform_cpu_enable(unsigned int cpu);
+
#endif /* ifndef __ASM_ARM_SMP_H */