[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>

4 files changed, 132 insertions, 0 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index dc6d8342e5e6..6b12d71978de 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -349,6 +349,13 @@ config NR_CPUS
         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 3284118f356b..9def4404e1f2 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -1050,3 +1050,34 @@ static int __init noirqdebug_setup(char *str)
 }
 
 __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 409db6d5ec99..ba298277becd 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 @@ void cpu_idle(void)
         /* 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 b40915dcd533..edb5a406922f 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -159,6 +159,91 @@ int __cpuinit __cpu_up(unsigned int cpu)
         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.