x86: I/O APIC: unmask the second-chance timer interrupt

Unmask the timer interrupt line set up in the through-8259A mode
explicitly after setup_timer_IRQ0_pin() has set up the I/O APIC interrupt
redirection entry to let the two operations be unbound from each other.
Signed-off-by: NMaciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/io_apic_32.c

@@ -2185,6 +2185,7 @@ static inline void __init check_timer(void)
 		 * legacy devices should be connected to IO APIC #0
 		 */
 		setup_timer_IRQ0_pin(apic2, pin2, vector);
+		unmask_IO_APIC_irq(0);
 		enable_8259A_irq(0);
 		if (timer_irq_works()) {
 			printk("works.\n");

arch/x86/kernel/io_apic_64.c

@@ -1691,6 +1691,7 @@ static inline void __init check_timer(void)
 		 * legacy devices should be connected to IO APIC #0
 		 */
 		setup_timer_IRQ0_pin(apic2, pin2, cfg->vector);
+		unmask_IO_APIC_irq(0);
 		enable_8259A_irq(0);
 		if (timer_irq_works()) {
 			apic_printk(APIC_VERBOSE," works.\n");