[PATCH 12/12] parisc: Implement __cpu_die() and __cpu_disable() for CPU hotplugging

[Helge Deller <deller@xxxxxx>]

Add relevant code to __cpu_die() and __cpu_disable() to finally enable
the CPU hotplugging features. Reset the irq count values in smp_callin()
to zero before bringing up the CPU.

Use "chcpu -d 1" to bring CPU1 down, and "chcpu -e 1" to bring it up.

Signed-off-by: Helge Deller <deller@xxxxxx>
---
 arch/parisc/Kconfig           |  1 +
 arch/parisc/include/asm/smp.h |  9 +---
 arch/parisc/kernel/smp.c      | 80 +++++++++++++++++++++++++++++++++--
 3 files changed, 79 insertions(+), 11 deletions(-)

diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 6bd42c82a019..ec5bb9626d06 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -56,6 +56,7 @@ config PARISC
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select GENERIC_SCHED_CLOCK
+	select GENERIC_IRQ_MIGRATION
 	select HAVE_UNSTABLE_SCHED_CLOCK if SMP
 	select LEGACY_TIMER_TICK
 	select CPU_NO_EFFICIENT_FFS
diff --git a/arch/parisc/include/asm/smp.h b/arch/parisc/include/asm/smp.h
index 2279ebe5e2da..94d1f21ce99a 100644
--- a/arch/parisc/include/asm/smp.h
+++ b/arch/parisc/include/asm/smp.h
@@ -44,12 +44,7 @@ static inline void smp_send_all_nop(void) { return; }

 #define NO_PROC_ID		0xFF		/* No processor magic marker */
 #define ANY_PROC_ID		0xFF		/* Any processor magic marker */
-static inline int __cpu_disable (void) {
-  return 0;
-}
-static inline void __cpu_die (unsigned int cpu) {
-  while(1)
-    ;
-}
+int __cpu_disable(void);
+void __cpu_die(unsigned int cpu);

 #endif /*  __ASM_SMP_H */
diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c
index a32a882a2d58..60cc33fd345c 100644
--- a/arch/parisc/kernel/smp.c
+++ b/arch/parisc/kernel/smp.c
@@ -30,6 +30,7 @@
 #include <linux/ftrace.h>
 #include <linux/cpu.h>
 #include <linux/kgdb.h>
+#include <linux/sched/hotplug.h>

 #include <linux/atomic.h>
 #include <asm/current.h>
@@ -309,7 +310,7 @@ smp_cpu_init(int cpunum)
  * Slaves start using C here. Indirectly called from smp_slave_stext.
  * Do what start_kernel() and main() do for boot strap processor (aka monarch)
  */
-void __init smp_callin(unsigned long pdce_proc)
+void __cpuinit smp_callin(unsigned long pdce_proc)
 {
 	int slave_id = cpu_now_booting;

@@ -339,6 +340,19 @@ int smp_boot_one_cpu(int cpuid, struct task_struct *idle)
 	const struct cpuinfo_parisc *p = &per_cpu(cpu_data, cpuid);
 	long timeout;

+#ifdef CONFIG_HOTPLUG_CPU
+	int i;
+
+	/* reset irq statistics for this CPU */
+	memset(&per_cpu(irq_stat, cpuid), 0, sizeof(irq_cpustat_t));
+	for (i = 0; i < NR_IRQS; i++) {
+		struct irq_desc *desc = irq_to_desc(i);
+
+		if (desc && desc->kstat_irqs)
+			*per_cpu_ptr(desc->kstat_irqs, cpuid) = 0;
+	}
+#endif
+
 	/* Let _start know what logical CPU we're booting
 	** (offset into init_tasks[],cpu_data[])
 	*/
@@ -430,10 +444,68 @@ void smp_cpus_done(unsigned int cpu_max)

 int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
-	if (cpu != 0 && cpu < parisc_max_cpus && smp_boot_one_cpu(cpu, tidle))
-		return -ENOSYS;
+	if (cpu_online(cpu))
+		return 0;
+
+	if (num_online_cpus() < parisc_max_cpus && smp_boot_one_cpu(cpu, tidle))
+		return -EIO;
+
+	return cpu_online(cpu) ? 0 : -EIO;
+}
+
+/*
+ * __cpu_disable runs on the processor to be shutdown.
+ */
+int __cpu_disable(void)
+{
+#ifdef CONFIG_HOTPLUG_CPU
+	unsigned int cpu = smp_processor_id();
+
+	remove_cpu_topology(cpu);
+
+	/*
+	 * 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);
+
+	/*
+	 * disable IPI interrupt
+	 */
+	disable_percpu_irq(IPI_IRQ);
+
+	/*
+	 * migrate IRQs away from this CPU
+	 */
+	irq_migrate_all_off_this_cpu();
+
+	/*
+	 * Flush user cache and TLB mappings, and then remove this CPU
+	 * from the vm mask set of all processes.
+	 *
+	 * Caches are flushed to the Level of Unification Inner Shareable
+	 * to write-back dirty lines to unified caches shared by all CPUs.
+	 */
+	flush_cache_all_local();
+	flush_tlb_all_local(NULL);

-	return cpu_online(cpu) ? 0 : -ENOSYS;
+	/* disable all irqs, including timer irq */
+	local_irq_disable();
+#endif
+	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 __cpu_die(unsigned int cpu)
+{
+	if (!cpu_wait_death(cpu, 5)) {
+		pr_crit("CPU%u: cpu didn't die\n", cpu);
+		return;
+	}
+	pr_debug("CPU%u: shutdown\n", cpu);
 }

 #ifdef CONFIG_PROC_FS
--
2.35.1