ia64: convert to legacy_timer_tick

ia64 is the only architecture that calls xtime_update() in a loop,
once for each jiffie that has passed since the last event.

Before commit 3171a0305d62 ("[PATCH] simplify update_times (avoid
jiffies/jiffies_64 aliasing problem)") in 2006, it could not actually do
this any differently, but now it seems simpler to just pass the number
of jiffies that passed in the meantime.

While this loses the ability process interrupts in the middle of
the timer tick by calling local_irq_enable(), doing so is fairly
peculiar anyway and it seems better to just do what everyone
else does here.

Reviewed-by: Linus Walleij <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>

arch/ia64/Kconfig

···
 	select ARCH_THREAD_STACK_ALLOCATOR
 	select ARCH_CLOCKSOURCE_DATA
 	select GENERIC_TIME_VSYSCALL
+	select LEGACY_TIMER_TICK
 	select SWIOTLB
 	select SYSCTL_ARCH_UNALIGN_NO_WARN
 	select HAVE_MOD_ARCH_SPECIFIC

arch/ia64/kernel/time.c

···
 static irqreturn_t
 timer_interrupt (int irq, void *dev_id)
 {
-	unsigned long new_itm;
+	unsigned long cur_itm, new_itm, ticks;
 
 	if (cpu_is_offline(smp_processor_id())) {
 		return IRQ_HANDLED;
 	}
 
 	new_itm = local_cpu_data->itm_next;
+	cur_itm = ia64_get_itc();
 
-	if (!time_after(ia64_get_itc(), new_itm))
+	if (!time_after(cur_itm, new_itm)) {
 		printk(KERN_ERR "Oops: timer tick before it's due (itc=%lx,itm=%lx)\n",
-		       ia64_get_itc(), new_itm);
-
-	profile_tick(CPU_PROFILING);
-
-	while (1) {
-		update_process_times(user_mode(get_irq_regs()));
-
-		new_itm += local_cpu_data->itm_delta;
-
-		if (smp_processor_id() == time_keeper_id)
-			xtime_update(1);
-
-		local_cpu_data->itm_next = new_itm;
-
-		if (time_after(new_itm, ia64_get_itc()))
-			break;
-
-		/*
-		 * Allow IPIs to interrupt the timer loop.
-		 */
-		local_irq_enable();
-		local_irq_disable();
+		       cur_itm, new_itm);
+		ticks = 1;
+	} else {
+		ticks = DIV_ROUND_UP(cur_itm - new_itm,
+				     local_cpu_data->itm_delta);
+		new_itm += ticks * local_cpu_data->itm_delta;
 	}
+
+	if (smp_processor_id() != time_keeper_id)
+		ticks = 0;
+
+	legacy_timer_tick(ticks);
 
 	do {
 		/*