x86, ioapic: Early enable ioapic for timer irq

Moorestown platform needs apic ready early for the system timer irq
which is delievered via ioapic.  Should not impact other platforms.

In the longer term, once ioapic setup is moved before late time init,
we will not need this patch to do early apic enabling.
Signed-off-by: Jacob Pan <jacob.jun.pan@intel.com>
LKML-Reference: <43F901BD926A4E43B106BF17856F07559FB80D07@orsmsx508.amr.corp.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/include/asm/io_apic.h

@@ -187,6 +187,7 @@ extern struct mp_ioapic_gsi  mp_gsi_routing[];
 int mp_find_ioapic(int gsi);
 int mp_find_ioapic_pin(int ioapic, int gsi);
 void __init mp_register_ioapic(int id, u32 address, u32 gsi_base);
+extern void __init pre_init_apic_IRQ0(void);
 
 #else  /* !CONFIG_X86_IO_APIC */
 

arch/x86/kernel/apic/io_apic.c

@@ -4289,3 +4289,24 @@ void __init mp_register_ioapic(int id, u32 address, u32 gsi_base)
 
 	nr_ioapics++;
 }
+
+/* Enable IOAPIC early just for system timer */
+void __init pre_init_apic_IRQ0(void)
+{
+	struct irq_cfg *cfg;
+	struct irq_desc *desc;
+
+	printk(KERN_INFO "Early APIC setup for system timer0\n");
+#ifndef CONFIG_SMP
+	phys_cpu_present_map = physid_mask_of_physid(boot_cpu_physical_apicid);
+#endif
+	desc = irq_to_desc_alloc_node(0, 0);
+
+	setup_local_APIC();
+
+	cfg = irq_cfg(0);
+	add_pin_to_irq_node(cfg, 0, 0, 0);
+	set_irq_chip_and_handler_name(0, &ioapic_chip, handle_edge_irq, "edge");
+
+	setup_IO_APIC_irq(0, 0, 0, desc, 0, 0);
+}