x86: keep MP_intsrc_info untouched if we do not update mptable

Daniel Exner reported IO-APIC enumeration breakage in linux-next.

Alexey Starikovskiy found out that it might be related to
commit 2944e16b "x86: update mptable".

use enable_update_mptable to decide if need check before add mp_irqs array.
Reported-by: Daniel Exner <webmaster@dragonslave.de>
Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/acpi/boot.c

@@ -1172,6 +1172,9 @@ int mp_config_acpi_gsi(unsigned char number, unsigned int devfn, u8 pin,
 	struct mpc_config_intsrc intsrc;
 	int ioapic;
 
+	if (!enable_update_mptable)
+		return 0;
+
 	/* print the entry should happen on mptable identically */
 	intsrc.mpc_type = MP_INTSRC;
 	intsrc.mpc_irqtype = mp_INT;

arch/x86/kernel/mpparse.c

@@ -34,6 +34,8 @@
 #include <mach_mpparse.h>
 #endif
 
+int enable_update_mptable;
+
 /*
  * Checksum an MP configuration block.
  */
@@ -295,10 +297,11 @@ void MP_intsrc_info(struct mpc_config_intsrc *m)
 
 	print_MP_intsrc_info(m);
 
-	for (i = 0; i < mp_irq_entries; i++) {
-		if (!mp_irq_mpc_intsrc_cmp(&mp_irqs[i], m))
-			return;
-	}
+	if (enable_update_mptable)
+		for (i = 0; i < mp_irq_entries; i++) {
+			if (!mp_irq_mpc_intsrc_cmp(&mp_irqs[i], m))
+				return;
+		}
 
 	assign_to_mp_irq(m, &mp_irqs[mp_irq_entries]);
 	if (++mp_irq_entries == MAX_IRQ_SOURCES)
@@ -1110,8 +1113,6 @@ static int  __init replace_intsrc_all(struct mp_config_table *mpc,
 	return 0;
 }
 
-int __initdata enable_update_mptable;
-
 static int __init update_mptable_setup(char *str)
 {
 	enable_update_mptable = 1;

include/asm-x86/mpspec.h

@@ -61,6 +61,7 @@ extern void mp_config_acpi_legacy_irqs(void);
 extern int mp_register_gsi(u32 gsi, int edge_level, int active_high_low);
 extern void MP_intsrc_info(struct mpc_config_intsrc *m);
 #ifdef CONFIG_X86_IO_APIC
+extern int enable_update_mptable;
 extern int mp_config_acpi_gsi(unsigned char number, unsigned int devfn, u8 pin,
 				u32 gsi, int triggering, int polarity);
 #else