3 files changed, 21 insertions, 4 deletions

diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h
index e854c7ab4169..65228ccc5f0d 100644
--- a/arch/x86/include/asm/timer.h
+++ b/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;
 
diff --git a/arch/x86/kernel/time_32.c b/arch/x86/kernel/time_32.c
index acbaefd61e8e..7a26bcf887f6 100644
--- a/arch/x86/kernel/time_32.c
+++ b/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);
 
diff --git a/arch/x86/kernel/time_64.c b/arch/x86/kernel/time_64.c
index 45914f8844a7..35e0a925da56 100644
--- a/arch/x86/kernel/time_64.c
+++ b/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