parisc: Find a new timesync master if current CPU is removed

When CPU hotplugging is enabled, the user may want to remove the
current CPU which is providing the timer ticks. If this happens
we need to find a new timesync master.

Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/include/asm/processor.h

@@ -95,6 +95,7 @@ struct cpuinfo_parisc {
 
 extern struct system_cpuinfo_parisc boot_cpu_data;
 DECLARE_PER_CPU(struct cpuinfo_parisc, cpu_data);
+extern int time_keeper_id;		/* CPU used for timekeeping */
 
 #define CPU_HVERSION ((boot_cpu_data.hversion >> 4) & 0x0FFF)
 

arch/parisc/kernel/smp.c

@@ -465,6 +465,12 @@ int __cpu_disable(void)
 	 */
 	set_cpu_online(cpu, false);
 
+	/* Find a new timesync master */
+	if (cpu == time_keeper_id) {
+		time_keeper_id = cpumask_first(cpu_online_mask);
+		pr_info("CPU %d is now promoted to time-keeper master\n", time_keeper_id);
+	}
+
 	disable_percpu_irq(IPI_IRQ);
 
 	irq_migrate_all_off_this_cpu();

arch/parisc/kernel/time.c

@@ -40,6 +40,8 @@
 
 #include <linux/timex.h>
 
+int time_keeper_id __read_mostly;	/* CPU used for timekeeping. */
+
 static unsigned long clocktick __ro_after_init;	/* timer cycles per tick */
 
 /*
@@ -84,7 +86,7 @@ irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id)
 	cpuinfo->it_value = next_tick;
 
 	/* Go do system house keeping. */
-	if (cpu != 0)
+	if (IS_ENABLED(CONFIG_SMP) && (cpu != time_keeper_id))
 		ticks_elapsed = 0;
 	legacy_timer_tick(ticks_elapsed);