powerpc/powernv: Add CPU hotplug support

Unplugged CPU go into NAP mode in a loop until woken up

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

2 files changed, 78 insertions, 2 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 62711421cd64..8523bd1b8d7e 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -323,7 +323,7 @@ config SWIOTLB
 
 config HOTPLUG_CPU
         bool "Support for enabling/disabling CPUs"
-        depends on SMP && HOTPLUG && EXPERIMENTAL && (PPC_PSERIES || PPC_PMAC)
+        depends on SMP && HOTPLUG && EXPERIMENTAL && (PPC_PSERIES || PPC_PMAC || PPC_POWERNV)
         ---help---
           Say Y here to be able to disable and re-enable individual
           CPUs at runtime on SMP machines.
diff --git a/arch/powerpc/platforms/powernv/smp.c b/arch/powerpc/platforms/powernv/smp.c
index 36c715102c58..4f4ec3797eb6 100644
--- a/arch/powerpc/platforms/powernv/smp.c
+++ b/arch/powerpc/platforms/powernv/smp.c
@@ -33,7 +33,14 @@
 
 #include "powernv.h"
 
-static void __devinit pnv_smp_setup_cpu(int cpu)
+#ifdef DEBUG
+#include <asm/udbg.h>
+#define DBG(fmt...) udbg_printf(fmt)
+#else
+#define DBG(fmt...)
+#endif
+
+static void __cpuinit pnv_smp_setup_cpu(int cpu)
 {
         if (cpu != boot_cpuid)
                 xics_setup_cpu();
@@ -55,6 +62,67 @@ static int pnv_smp_cpu_bootable(unsigned int nr)
         return 1;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+static int pnv_smp_cpu_disable(void)
+{
+        int cpu = smp_processor_id();
+
+        /* This is identical to pSeries... might consolidate by
+         * moving migrate_irqs_away to a ppc_md with default to
+         * the generic fixup_irqs. --BenH.
+         */
+        set_cpu_online(cpu, false);
+        vdso_data->processorCount--;
+        if (cpu == boot_cpuid)
+                boot_cpuid = cpumask_any(cpu_online_mask);
+        xics_migrate_irqs_away();
+        return 0;
+}
+
+static void pnv_smp_cpu_kill_self(void)
+{
+        unsigned int cpu;
+
+        /* If powersave_nap is enabled, use NAP mode, else just
+         * spin aimlessly
+         */
+        if (!powersave_nap) {
+                generic_mach_cpu_die();
+                return;
+        }
+
+        /* Standard hot unplug procedure */
+        local_irq_disable();
+        idle_task_exit();
+        current->active_mm = NULL; /* for sanity */
+        cpu = smp_processor_id();
+        DBG("CPU%d offline\n", cpu);
+        generic_set_cpu_dead(cpu);
+        smp_wmb();
+
+        /* We don't want to take decrementer interrupts while we are offline,
+         * so clear LPCR:PECE1. We keep PECE2 enabled.
+         */
+        mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) & ~(u64)LPCR_PECE1);
+        while (!generic_check_cpu_restart(cpu)) {
+                power7_idle();
+                if (!generic_check_cpu_restart(cpu)) {
+                        DBG("CPU%d Unexpected exit while offline !\n", cpu);
+                        /* We may be getting an IPI, so we re-enable
+                         * interrupts to process it, it will be ignored
+                         * since we aren't online (hopefully)
+                         */
+                        local_irq_enable();
+                        local_irq_disable();
+                }
+        }
+        mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) | LPCR_PECE1);
+        DBG("CPU%d coming online...\n", cpu);
+}
+
+#endif /* CONFIG_HOTPLUG_CPU */
+
 static struct smp_ops_t pnv_smp_ops = {
         .message_pass   = smp_muxed_ipi_message_pass,
         .cause_ipi      = NULL, /* Filled at runtime by xics_smp_probe() */
@@ -62,6 +130,10 @@ static struct smp_ops_t pnv_smp_ops = {
         .kick_cpu       = smp_generic_kick_cpu,
         .setup_cpu      = pnv_smp_setup_cpu,
         .cpu_bootable   = pnv_smp_cpu_bootable,
+#ifdef CONFIG_HOTPLUG_CPU
+        .cpu_disable    = pnv_smp_cpu_disable,
+        .cpu_die        = generic_cpu_die,
+#endif /* CONFIG_HOTPLUG_CPU */
 };
 
 /* This is called very early during platform setup_arch */
@@ -80,4 +152,8 @@ void __init pnv_smp_init(void)
                 smp_ops->take_timebase = rtas_take_timebase;
         }
 #endif /* CONFIG_PPC_RTAS */
+
+#ifdef CONFIG_HOTPLUG_CPU
+        ppc_md.cpu_die  = pnv_smp_cpu_kill_self;
+#endif
 }