[PATCH] ppc32: support hotplug cpu on powermacs

This allows cpus to be off-lined on 32-bit SMP powermacs.  When a cpu
is off-lined, it is put into sleep mode with interrupts disabled.  It
can be on-lined again by asserting its soft-reset pin, which is
connected to a GPIO pin.

With this I can off-line the second cpu in my dual G4 powermac, which
means that I can then suspend the machine (the suspend/resume code
refuses to suspend if more than one cpu is online, and making it cope
with multiple cpus is surprisingly messy).

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 30 insertions, 14 deletions

diff --git a/arch/ppc/kernel/smp.c b/arch/ppc/kernel/smp.c
index e70b587b9e51..726fe7ce1747 100644
--- a/arch/ppc/kernel/smp.c
+++ b/arch/ppc/kernel/smp.c
@@ -45,6 +45,7 @@ cpumask_t cpu_online_map;
 cpumask_t cpu_possible_map;
 int smp_hw_index[NR_CPUS];
 struct thread_info *secondary_ti;
+static struct task_struct *idle_tasks[NR_CPUS];
 
 EXPORT_SYMBOL(cpu_online_map);
 EXPORT_SYMBOL(cpu_possible_map);
@@ -286,7 +287,8 @@ static void __devinit smp_store_cpu_info(int id)
 
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
-        int num_cpus, i;
+        int num_cpus, i, cpu;
+        struct task_struct *p;
 
         /* Fixup boot cpu */
         smp_store_cpu_info(smp_processor_id());
@@ -308,6 +310,17 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 
         if (smp_ops->space_timers)
                 smp_ops->space_timers(num_cpus);
+
+        for_each_cpu(cpu) {
+                if (cpu == smp_processor_id())
+                        continue;
+                /* create a process for the processor */
+                p = fork_idle(cpu);
+                if (IS_ERR(p))
+                        panic("failed fork for CPU %u: %li", cpu, PTR_ERR(p));
+                p->thread_info->cpu = cpu;
+                idle_tasks[cpu] = p;
+        }
 }
 
 void __devinit smp_prepare_boot_cpu(void)
@@ -334,12 +347,17 @@ int __devinit start_secondary(void *unused)
         set_dec(tb_ticks_per_jiffy);
         cpu_callin_map[cpu] = 1;
 
-        printk("CPU %i done callin...\n", cpu);
+        printk("CPU %d done callin...\n", cpu);
         smp_ops->setup_cpu(cpu);
-        printk("CPU %i done setup...\n", cpu);
-        local_irq_enable();
+        printk("CPU %d done setup...\n", cpu);
         smp_ops->take_timebase();
-        printk("CPU %i done timebase take...\n", cpu);
+        printk("CPU %d done timebase take...\n", cpu);
+
+        spin_lock(&call_lock);
+        cpu_set(cpu, cpu_online_map);
+        spin_unlock(&call_lock);
+
+        local_irq_enable();
 
         cpu_idle();
         return 0;
@@ -347,17 +365,11 @@ int __devinit start_secondary(void *unused)
 
 int __cpu_up(unsigned int cpu)
 {
-        struct task_struct *p;
         char buf[32];
         int c;
 
-        /* create a process for the processor */
-        /* only regs.msr is actually used, and 0 is OK for it */
-        p = fork_idle(cpu);
-        if (IS_ERR(p))
-                panic("failed fork for CPU %u: %li", cpu, PTR_ERR(p));
-        secondary_ti = p->thread_info;
-        p->thread_info->cpu = cpu;
+        secondary_ti = idle_tasks[cpu]->thread_info;
+        mb();
 
         /*
          * There was a cache flush loop here to flush the cache
@@ -389,7 +401,11 @@ int __cpu_up(unsigned int cpu)
         printk("Processor %d found.\n", cpu);
 
         smp_ops->give_timebase();
-        cpu_set(cpu, cpu_online_map);
+
+        /* Wait until cpu puts itself in the online map */
+        while (!cpu_online(cpu))
+                cpu_relax();
+
         return 0;
 }