x86-iommu: provide x86_iommu_get_default

Instead of searching the device tree every time, one static variable is
declared for the default system x86 IOMMU device.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/acpi-build.c

@@ -52,7 +52,7 @@
 #include "hw/i386/ich9.h"
 #include "hw/pci/pci_bus.h"
 #include "hw/pci-host/q35.h"
-#include "hw/i386/intel_iommu.h"
+#include "hw/i386/x86-iommu.h"
 #include "hw/timer/hpet.h"
 
 #include "hw/acpi/aml-build.h"
@@ -2539,12 +2539,7 @@ static bool acpi_get_mcfg(AcpiMcfgInfo *mcfg)
 
 static bool acpi_has_iommu(void)
 {
-    bool ambiguous;
+    return !!x86_iommu_get_default();
-    Object *intel_iommu;
-
-    intel_iommu = object_resolve_path_type("", TYPE_INTEL_IOMMU_DEVICE,
-                                           &ambiguous);
-    return intel_iommu && !ambiguous;
 }
 
 static

hw/i386/x86-iommu.c

@@ -21,6 +21,28 @@
 #include "hw/sysbus.h"
 #include "hw/boards.h"
 #include "hw/i386/x86-iommu.h"
+#include "qemu/error-report.h"
+
+/* Default X86 IOMMU device */
+static X86IOMMUState *x86_iommu_default = NULL;
+
+static void x86_iommu_set_default(X86IOMMUState *x86_iommu)
+{
+    assert(x86_iommu);
+
+    if (x86_iommu_default) {
+        error_report("QEMU does not support multiple vIOMMUs "
+                     "for x86 yet.");
+        exit(1);
+    }
+
+    x86_iommu_default = x86_iommu;
+}
+
+X86IOMMUState *x86_iommu_get_default(void)
+{
+    return x86_iommu_default;
+}
 
 static void x86_iommu_realize(DeviceState *dev, Error **errp)
 {
@@ -28,6 +50,7 @@ static void x86_iommu_realize(DeviceState *dev, Error **errp)
     if (x86_class->realize) {
         x86_class->realize(dev, errp);
     }
+    x86_iommu_set_default(X86_IOMMU_DEVICE(dev));
 }
 
 static void x86_iommu_class_init(ObjectClass *klass, void *data)

include/hw/i386/x86-iommu.h

@@ -45,4 +45,10 @@ struct X86IOMMUState {
     SysBusDevice busdev;
 };
 
+/**
+ * x86_iommu_get_default - get default IOMMU device
+ * @return: pointer to default IOMMU device
+ */
+X86IOMMUState *x86_iommu_get_default(void);
+
 #endif