x86: add mp_find_ioapic_pin

Add mp_find_ioapic_pin() to find an IO APIC's specific pin from a GSI,
and use this function within acpi/boot.  Make it non-static so other
code can use it too.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

arch/x86/include/asm/mpspec.h

@@ -78,6 +78,7 @@ extern int acpi_probe_gsi(void);
 extern int mp_config_acpi_gsi(unsigned char number, unsigned int devfn, u8 pin,
 				u32 gsi, int triggering, int polarity);
 extern int mp_find_ioapic(int gsi);
+extern int mp_find_ioapic_pin(int ioapic, int gsi);
 #else
 static inline int
 mp_config_acpi_gsi(unsigned char number, unsigned int devfn, u8 pin,

arch/x86/kernel/acpi/boot.c

@@ -887,6 +887,16 @@ int mp_find_ioapic(int gsi)
 	return -1;
 }
 
+int mp_find_ioapic_pin(int ioapic, int gsi)
+{
+	if (WARN_ON(ioapic == -1))
+		return -1;
+	if (WARN_ON(gsi > mp_ioapic_routing[ioapic].gsi_end))
+		return -1;
+
+	return gsi - mp_ioapic_routing[ioapic].gsi_base;
+}
+
 static u8 __init uniq_ioapic_id(u8 id)
 {
 #ifdef CONFIG_X86_32
@@ -1022,7 +1032,7 @@ void __init mp_override_legacy_irq(u8 bus_irq, u8 polarity, u8 trigger, u32 gsi)
 	ioapic = mp_find_ioapic(gsi);
 	if (ioapic < 0)
 		return;
-	pin = gsi - mp_ioapic_routing[ioapic].gsi_base;
+	pin = mp_find_ioapic_pin(ioapic, gsi);
 
 	/*
 	 * TBD: This check is for faulty timer entries, where the override
@@ -1142,7 +1152,7 @@ int mp_register_gsi(u32 gsi, int triggering, int polarity)
 		return gsi;
 	}
 
-	ioapic_pin = gsi - mp_ioapic_routing[ioapic].gsi_base;
+	ioapic_pin = mp_find_ioapic_pin(ioapic, gsi);
 
 #ifdef CONFIG_X86_32
 	if (ioapic_renumber_irq)
@@ -1231,7 +1241,7 @@ int mp_config_acpi_gsi(unsigned char number, unsigned int devfn, u8 pin,
 	mp_irq.srcbusirq = (((devfn >> 3) & 0x1f) << 2) | ((pin - 1) & 3);
 	ioapic = mp_find_ioapic(gsi);
 	mp_irq.dstapic = mp_ioapic_routing[ioapic].apic_id;
-	mp_irq.dstirq = gsi - mp_ioapic_routing[ioapic].gsi_base;
+	mp_irq.dstirq = mp_find_ioapic_pin(ioapic, gsi);
 
 	save_mp_irq(&mp_irq);
 #endif