diff --git a/include/sysemu/host_iommu_device.h b/include/sysemu/host_iommu_device.h
index db47a16..a578739 100644
--- a/include/sysemu/host_iommu_device.h
+++ b/include/sysemu/host_iommu_device.h
@@ -15,6 +15,18 @@
 #include "qom/object.h"
 #include "qapi/error.h"
 
+/**
+ * struct HostIOMMUDeviceCaps - Define host IOMMU device capabilities.
+ *
+ * @type: host platform IOMMU type.
+ *
+ * @aw_bits: host IOMMU address width. 0xff if no limitation.
+ */
+typedef struct HostIOMMUDeviceCaps {
+    uint32_t type;
+    uint8_t aw_bits;
+} HostIOMMUDeviceCaps;
+
 #define TYPE_HOST_IOMMU_DEVICE "host-iommu-device"
 OBJECT_DECLARE_TYPE(HostIOMMUDevice, HostIOMMUDeviceClass, HOST_IOMMU_DEVICE)
 
@@ -22,6 +34,7 @@
     Object parent_obj;
 
     char *name;
+    HostIOMMUDeviceCaps caps;
 };
 
 /**
@@ -49,5 +62,30 @@
      * Returns: true on success, false on failure.
      */
     bool (*realize)(HostIOMMUDevice *hiod, void *opaque, Error **errp);
+    /**
+     * @get_cap: check if a host IOMMU device capability is supported.
+     *
+     * Optional callback, if not implemented, hint not supporting query
+     * of @cap.
+     *
+     * @hiod: pointer to a host IOMMU device instance.
+     *
+     * @cap: capability to check.
+     *
+     * @errp: pass an Error out when fails to query capability.
+     *
+     * Returns: <0 on failure, 0 if a @cap is unsupported, or else
+     * 1 or some positive value for some special @cap,
+     * i.e., HOST_IOMMU_DEVICE_CAP_AW_BITS.
+     */
+    int (*get_cap)(HostIOMMUDevice *hiod, int cap, Error **errp);
 };
+
+/*
+ * Host IOMMU device capability list.
+ */
+#define HOST_IOMMU_DEVICE_CAP_IOMMU_TYPE        0
+#define HOST_IOMMU_DEVICE_CAP_AW_BITS           1
+
+#define HOST_IOMMU_DEVICE_CAP_AW_BITS_MAX       64
 #endif