x86: Simplify timer_ack magic in time_32.c

Let the compiler optimize the timer_ack magic away in the 32bit timer
interrupt and put the same code into time_64.c. It's optimized out for
CONFIG_X86_IO_APIC on 32bit and for 64bit because timer_ack is const 0
in both cases.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/include/asm/timer.h

@@ -9,11 +9,13 @@
 
 unsigned long long native_sched_clock(void);
 unsigned long native_calibrate_tsc(void);
+extern int recalibrate_cpu_khz(void);
 
-#ifdef CONFIG_X86_32
+#if defined(CONFIG_X86_32) && defined(CONFIG_X86_IO_APIC)
 extern int timer_ack;
+#else
+# define timer_ack (0)
 #endif
-extern int recalibrate_cpu_khz(void);
 
 extern int no_timer_check;
 

arch/x86/kernel/time_32.c

@@ -23,7 +23,9 @@
 #include <asm/time.h>
 #include <asm/nmi.h>
 
+#if defined(CONFIG_X86_32) && defined(CONFIG_X86_IO_APIC)
 int timer_ack;
+#endif
 
 unsigned long profile_pc(struct pt_regs *regs)
 {
@@ -60,7 +62,7 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id)
 	/* Keep nmi watchdog up to date */
 	inc_irq_stat(irq0_irqs);
 
-#ifdef CONFIG_X86_IO_APIC
+	/* Optimized out for !IO_APIC and x86_64 */
 	if (timer_ack) {
 		/*
 		 * Subtle, when I/O APICs are used we have to ack timer IRQ
@@ -73,7 +75,6 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id)
 		inb(PIC_MASTER_POLL);
 		spin_unlock(&i8259A_lock);
 	}
-#endif
 
 	global_clock_event->event_handler(global_clock_event);
 

arch/x86/kernel/time_64.c

@@ -51,6 +51,20 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id)
 {
 	inc_irq_stat(irq0_irqs);
 
+	/* Optimized out for !IO_APIC and x86_64 */
+	if (timer_ack) {
+		/*
+		 * Subtle, when I/O APICs are used we have to ack timer IRQ
+		 * manually to deassert NMI lines for the watchdog if run
+		 * on an 82489DX-based system.
+		 */
+		spin_lock(&i8259A_lock);
+		outb(0x0c, PIC_MASTER_OCW3);
+		/* Ack the IRQ; AEOI will end it automatically. */
+		inb(PIC_MASTER_POLL);
+		spin_unlock(&i8259A_lock);
+	}
+
 	global_clock_event->event_handler(global_clock_event);
 
 #ifdef CONFIG_MCA