xen/pci: Move check for acpi_sci_override_gsi to xen_setup_acpi_sci.

Previously we would check for acpi_sci_override_gsi == gsi every time
a PCI device was enabled. That works during early bootup, but later
on it could lead to triggering unnecessarily the acpi_gsi_to_irq(..) lookup.
The reason is that acpi_sci_override_gsi was declared in __initdata and
after early bootup could contain bogus values.

This patch moves the check for acpi_sci_override_gsi to the
site where the ACPI SCI is preset.

CC: stable@kernel.org
Reported-by: Raghavendra D Prabhu <rprabhu@wnohang.net>
Tested-by: Raghavendra D Prabhu <rprabhu@wnohang.net>
[http://lists.xensource.com/archives/html/xen-devel/2011-07/msg00154.html]
Suggested-by: Ian Campbell <ijc@hellion.org.uk>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/pci/xen.c

@@ -327,13 +327,12 @@ int __init pci_xen_hvm_init(void)
 }
 
 #ifdef CONFIG_XEN_DOM0
-static int xen_register_pirq(u32 gsi, int triggering)
+static int xen_register_pirq(u32 gsi, int gsi_override, int triggering)
 {
 	int rc, pirq, irq = -1;
 	struct physdev_map_pirq map_irq;
 	int shareable = 0;
 	char *name;
-	bool gsi_override = false;
 
 	if (!xen_pv_domain())
 		return -1;
@@ -345,31 +344,12 @@ static int xen_register_pirq(u32 gsi, int triggering)
 		shareable = 1;
 		name = "ioapic-level";
 	}
-
 	pirq = xen_allocate_pirq_gsi(gsi);
 	if (pirq < 0)
 		goto out;
 
-	/* Before we bind the GSI to a Linux IRQ, check whether
-	 * we need to override it with bus_irq (IRQ) value. Usually for
-	 * IRQs below IRQ_LEGACY_IRQ this holds IRQ == GSI, as so:
-	 *  ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 low level)
-	 * but there are oddballs where the IRQ != GSI:
-	 *  ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 20 low level)
-	 * which ends up being: gsi_to_irq[9] == 20
-	 * (which is what acpi_gsi_to_irq ends up calling when starting the
-	 * the ACPI interpreter and keels over since IRQ 9 has not been
-	 * setup as we had setup IRQ 20 for it).
-	 */
-	if (gsi == acpi_sci_override_gsi) {
-		/* Check whether the GSI != IRQ */
-		acpi_gsi_to_irq(gsi, &irq);
-		if (irq != gsi)
-			/* Bugger, we MUST have that IRQ. */
-			gsi_override = true;
-	}
-	if (gsi_override)
-		irq = xen_bind_pirq_gsi_to_irq(irq, pirq, shareable, name);
+	if (gsi_override >= 0)
+		irq = xen_bind_pirq_gsi_to_irq(gsi_override, pirq, shareable, name);
 	else
 		irq = xen_bind_pirq_gsi_to_irq(gsi, pirq, shareable, name);
 	if (irq < 0)
@@ -392,7 +372,7 @@ static int xen_register_pirq(u32 gsi, int triggering)
 	return irq;
 }
 
-static int xen_register_gsi(u32 gsi, int triggering, int polarity)
+static int xen_register_gsi(u32 gsi, int gsi_override, int triggering, int polarity)
 {
 	int rc, irq;
 	struct physdev_setup_gsi setup_gsi;
@@ -403,7 +383,7 @@ static int xen_register_gsi(u32 gsi, int triggering, int polarity)
 	printk(KERN_DEBUG "xen: registering gsi %u triggering %d polarity %d\n",
 			gsi, triggering, polarity);
 
-	irq = xen_register_pirq(gsi, triggering);
+	irq = xen_register_pirq(gsi, gsi_override, triggering);
 
 	setup_gsi.gsi = gsi;
 	setup_gsi.triggering = (triggering == ACPI_EDGE_SENSITIVE ? 0 : 1);
@@ -425,6 +405,8 @@ static __init void xen_setup_acpi_sci(void)
 	int rc;
 	int trigger, polarity;
 	int gsi = acpi_sci_override_gsi;
+	int irq = -1;
+	int gsi_override = -1;
 
 	if (!gsi)
 		return;
@@ -441,7 +423,25 @@ static __init void xen_setup_acpi_sci(void)
 	printk(KERN_INFO "xen: sci override: global_irq=%d trigger=%d "
 			"polarity=%d\n", gsi, trigger, polarity);
 
-	gsi = xen_register_gsi(gsi, trigger, polarity);
+	/* Before we bind the GSI to a Linux IRQ, check whether
+	 * we need to override it with bus_irq (IRQ) value. Usually for
+	 * IRQs below IRQ_LEGACY_IRQ this holds IRQ == GSI, as so:
+	 *  ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 low level)
+	 * but there are oddballs where the IRQ != GSI:
+	 *  ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 20 low level)
+	 * which ends up being: gsi_to_irq[9] == 20
+	 * (which is what acpi_gsi_to_irq ends up calling when starting the
+	 * the ACPI interpreter and keels over since IRQ 9 has not been
+	 * setup as we had setup IRQ 20 for it).
+	 */
+	/* Check whether the GSI != IRQ */
+	if (acpi_gsi_to_irq(gsi, &irq) == 0) {
+		if (irq >= 0 && irq != gsi)
+			/* Bugger, we MUST have that IRQ. */
+			gsi_override = irq;
+	}
+
+	gsi = xen_register_gsi(gsi, gsi_override, trigger, polarity);
 	printk(KERN_INFO "xen: acpi sci %d\n", gsi);
 
 	return;
@@ -450,7 +450,7 @@ static __init void xen_setup_acpi_sci(void)
 static int acpi_register_gsi_xen(struct device *dev, u32 gsi,
 				 int trigger, int polarity)
 {
-	return xen_register_gsi(gsi, trigger, polarity);
+	return xen_register_gsi(gsi, -1 /* no GSI override */, trigger, polarity);
 }
 
 static int __init pci_xen_initial_domain(void)
@@ -489,7 +489,7 @@ void __init xen_setup_pirqs(void)
 		if (acpi_get_override_irq(irq, &trigger, &polarity) == -1)
 			continue;
 
-		xen_register_pirq(irq,
+		xen_register_pirq(irq, -1 /* no GSI override */,
 			trigger ? ACPI_LEVEL_SENSITIVE : ACPI_EDGE_SENSITIVE);
 	}
 }