parisc: Rewrite arch_cpu_idle_dead() for CPU hotplugging

Let the PDC firmware put the CPU into firmware idle loop with the
pdc_cpu_rendezvous() function.
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/kernel/process.c

@@ -38,6 +38,7 @@
 #include <linux/rcupdate.h>
 #include <linux/random.h>
 #include <linux/nmi.h>
+#include <linux/sched/hotplug.h>
 
 #include <asm/io.h>
 #include <asm/asm-offsets.h>
@@ -46,6 +47,7 @@
 #include <asm/pdc_chassis.h>
 #include <asm/unwind.h>
 #include <asm/sections.h>
+#include <asm/cacheflush.h>
 
 #define COMMAND_GLOBAL  F_EXTEND(0xfffe0030)
 #define CMD_RESET       5       /* reset any module */
@@ -158,10 +160,29 @@ void release_thread(struct task_struct *dead_task)
 int running_on_qemu __ro_after_init;
 EXPORT_SYMBOL(running_on_qemu);
 
-void __cpuidle arch_cpu_idle_dead(void)
+/*
+ * Called from the idle thread for the CPU which has been shutdown.
+ */
+void arch_cpu_idle_dead(void)
 {
-	/* nop on real hardware, qemu will offline CPU. */
-	asm volatile("or %%r31,%%r31,%%r31\n":::);
+#ifdef CONFIG_HOTPLUG_CPU
+	idle_task_exit();
+
+	local_irq_disable();
+
+	/* Tell __cpu_die() that this CPU is now safe to dispose of. */
+	(void)cpu_report_death();
+
+	/* Ensure that the cache lines are written out. */
+	flush_cache_all_local();
+	flush_tlb_all_local(NULL);
+
+	/* Let PDC firmware put CPU into firmware idle loop. */
+	__pdc_cpu_rendezvous();
+
+	pr_warn("PDC does not provide rendezvous function.\n");
+#endif
+	while (1);
 }
 
 void __cpuidle arch_cpu_idle(void)