parisc: Implement __cpu_die() and __cpu_disable() for CPU hotplugging

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.

It seems that the firmware may need up to 8 seconds to fully stop a CPU
in which no other PDC calls are allowed to be made. Use a timeout
__cpu_die() to accommodate for this.

Use "chcpu -d 1" to bring CPU1 down, and "chcpu -e 1" to bring it up.
Signed-off-by: Helge Deller <deller@gmx.de>

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 if SMP
 	select HAVE_UNSTABLE_SCHED_CLOCK if SMP
 	select LEGACY_TIMER_TICK
 	select CPU_NO_EFFICIENT_FFS

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 */

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>
@@ -60,8 +61,6 @@ volatile struct task_struct *smp_init_current_idle_task;
 /* track which CPU is booting */
 static volatile int cpu_now_booting;
 
-static int parisc_max_cpus = 1;
-
 static DEFINE_PER_CPU(spinlock_t, ipi_lock);
 
 enum ipi_message_type {
@@ -269,7 +268,7 @@ void arch_send_call_function_single_ipi(int cpu)
 /*
  * Called by secondaries to update state and initialize CPU registers.
  */
-static void __init
+static void
 smp_cpu_init(int cpunum)
 {
 	extern void init_IRQ(void);    /* arch/parisc/kernel/irq.c */
@@ -309,7 +308,7 @@ 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 smp_callin(unsigned long pdce_proc)
 {
 	int slave_id = cpu_now_booting;
 
@@ -334,11 +333,28 @@ void __init smp_callin(unsigned long pdce_proc)
 /*
  * Bring one cpu online.
  */
-int smp_boot_one_cpu(int cpuid, struct task_struct *idle)
+static 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
+
+	/* wait until last booting CPU has started. */
+	while (cpu_now_booting)
+		;
+
 	/* Let _start know what logical CPU we're booting
 	** (offset into init_tasks[],cpu_data[])
 	*/
@@ -374,7 +390,6 @@ int smp_boot_one_cpu(int cpuid, struct task_struct *idle)
 		if(cpu_online(cpuid)) {
 			/* Which implies Slave has started up */
 			cpu_now_booting = 0;
-			smp_init_current_idle_task = NULL;
 			goto alive ;
 		}
 		udelay(100);
@@ -415,25 +430,82 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 		spin_lock_init(&per_cpu(ipi_lock, cpu));
 
 	init_cpu_present(cpumask_of(0));
-
-	parisc_max_cpus = max_cpus;
-	if (!max_cpus)
-		printk(KERN_INFO "SMP mode deactivated.\n");
 }
 
 
-void smp_cpus_done(unsigned int cpu_max)
+void __init smp_cpus_done(unsigned int cpu_max)
 {
-	return;
 }
 
 
 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() < setup_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_percpu_irq(IPI_IRQ);
+
+	irq_migrate_all_off_this_cpu();
+
+	flush_cache_all_local();
+	flush_tlb_all_local(NULL);
+
+	/* disable all irqs, including timer irq */
+	local_irq_disable();
+
+	/* wait for next timer irq ... */
+	mdelay(1000/HZ+100);
+
+	/* ... and then clear all pending external irqs */
+	set_eiem(0);
+	mtctl(~0UL, CR_EIRR);
+	mfctl(CR_EIRR);
+	mtctl(0, CR_EIRR);
+#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)
+{
+	pdc_cpu_rendezvous_lock();
+
+	if (!cpu_wait_death(cpu, 5)) {
+		pr_crit("CPU%u: cpu didn't die\n", cpu);
+		return;
+	}
+	pr_info("CPU%u: is shutting down\n", cpu);
+
+	/* set task's state to interruptible sleep */
+	set_current_state(TASK_INTERRUPTIBLE);
+	schedule_timeout((IS_ENABLED(CONFIG_64BIT) ? 8:2) * HZ);
 
-	return cpu_online(cpu) ? 0 : -ENOSYS;
+	pdc_cpu_rendezvous_unlock();
 }
 
 #ifdef CONFIG_PROC_FS