diff --git a/devicemodel/hw/pci/pci_util.c b/devicemodel/hw/pci/pci_util.c
index 498afb342..4dd588a0f 100644
--- a/devicemodel/hw/pci/pci_util.c
+++ b/devicemodel/hw/pci/pci_util.c
@@ -16,6 +16,35 @@
 #include "pci_util.h"
 #include "log.h"
 
+#define MAX_LEN			(PCI_BUSMAX + 1)
+
+struct pci_device_info {
+	bool is_bridge;
+	int primary_bus;
+	int secondary_bus;
+	int subordinate_bus;
+	uint16_t bdf;
+	struct pci_device_info *parent;  /* pointer to its parent bridge */
+	struct pci_device_info *clist;  /* children list */
+
+	/* cache of all pci devices
+	 * FIXME: remove PCI_DEVICE_Q.  To cleanup pci device cache:
+	 * remove children, then remove parents
+	 */
+	TAILQ_ENTRY(pci_device_info) PCI_DEVICE_Q;
+};
+
+TAILQ_HEAD(ALL_PCI_DEVICES, pci_device_info);
+static struct ALL_PCI_DEVICES pci_device_q;
+
+static int pci_scanned;
+
+/* map bus to bridge
+ * assume only one pci domain in the system so the
+ * bus # in the pci hierarchy is unique.
+ */
+static struct pci_device_info *bus_map[MAX_LEN];
+
 /* find position of specified pci capability register*/
 int pci_find_cap(struct pci_device *pdev, const int cap_id)
 {
@@ -101,3 +130,204 @@ bool is_bridge(struct pci_device *pdev)
 
 	return ((hdr_type & PCIM_HDRTYPE) == PCIM_HDRTYPE_BRIDGE);
 }
+
+/* add new_child to parent's child list */
+static inline void
+add_child(struct pci_device_info *new_child,
+			struct pci_device_info *parent)
+{
+	new_child->clist = parent->clist;
+	parent->clist = new_child;
+
+	// it is important to reset the new_child's clist to null
+	new_child->clist = NULL;
+}
+
+/* get number of children on bus */
+int get_device_count_on_bus(int bus)
+{
+	int count = 0;
+	struct pci_device_info *bridge = bus_map[bus];
+	struct pci_device_info *next;
+
+	if (bridge == NULL)
+		return 0;
+
+	next = bridge->clist;
+
+	while (next != NULL) {
+		if (next->is_bridge)
+			count += get_device_count_on_bridge(bridge);
+		else
+			count++;
+
+		next = next->clist;
+	}
+
+	return count;
+}
+
+/* get number of children on bridge */
+int get_device_count_on_bridge(const struct pci_device_info *bridge_info)
+{
+	int count = 0;
+	int i, ret;
+
+	if (bridge_info == NULL)
+		return 0;
+
+	for (i = bridge_info->secondary_bus; i <= bridge_info->subordinate_bus; i++) {
+		ret = get_device_count_on_bus(i);
+		pr_info("%s: device_count on bus[%x]=%d.\n", __func__, i, ret);
+		count += ret;
+	}
+
+	return count;
+}
+
+/* build and cache pci hierarchy in one pci domain
+ * @pre: only one pci domain in the system.  Need revisit
+ * if there is more than one domain in the system.
+ */
+int scan_pci(void)
+{
+	int error = 0;
+	struct pci_device_iterator *iter;
+	struct pci_device *dev;
+	int i;
+
+	TAILQ_INIT(&pci_device_q);
+
+	pci_scanned = 1;
+
+	iter = pci_slot_match_iterator_create(NULL);
+	while ((dev = pci_device_next(iter)) != NULL) {
+		struct pci_device_info *pci_info = calloc(1, sizeof(struct pci_device_info));
+
+		if (pci_info == NULL) {
+			error = -ENOMEM;
+			pr_err("%s, %s: calloc", __func__, __LINE__);
+			goto done;
+		}
+
+		pci_info->parent = NULL;
+		pci_info->clist = NULL;
+
+		pci_info->bdf = PCI_BDF(dev->bus, dev->dev, dev->func);
+
+		TAILQ_INSERT_TAIL(&pci_device_q, pci_info, PCI_DEVICE_Q);
+
+		if (pci_info->bdf == 0) { /* host bridge */
+			bus_map[0] = pci_info;
+			continue;
+		}
+
+		if (is_bridge(dev)) {
+			pci_info->is_bridge = true;
+
+			pci_device_get_bridge_buses(dev, &(pci_info->primary_bus),
+						&(pci_info->secondary_bus), &(pci_info->subordinate_bus));
+
+			// put bus and bridge into bus_map
+			for (i = pci_info->secondary_bus; i <= pci_info->subordinate_bus; i++)
+				bus_map[i] = pci_info;
+		} else
+			pci_info->is_bridge = false;
+
+		// set its parent bridge
+		pci_info->parent = bus_map[dev->bus];
+
+		// add itself to its parent bridge's child list
+		add_child(pci_info, pci_info->parent);
+	}
+
+done:
+	if (error < 0)
+		clean_pci_cache();
+
+	pci_iterator_destroy(iter);
+
+	return error;
+}
+
+/* find bdf of pci device pdev's root port */
+struct pci_device * pci_find_root_port(const struct pci_device *pdev)
+{
+	struct pci_device *bdev;
+	int bus, dev, func;
+
+	struct pci_device_info *brdg = bus_map[pdev->bus];
+
+	for (;;) {
+		if (brdg == NULL)
+			return NULL;
+
+		bus = (brdg->bdf >> 8) & 0xFF;
+		dev = (brdg->bdf >> 3) & 0x1F;
+		func = brdg->bdf & 0x7;
+
+		bdev = pci_device_find_by_slot(0, bus, dev, func);
+		if (is_root_port(bdev))
+			return bdev;
+
+		brdg = brdg->parent;
+	}
+
+	return NULL;
+}
+
+/* clean cache of pci device: free all allocated memory */
+void clean_pci_cache(void)
+{
+	if (!pci_scanned)
+		return;
+
+	while (!TAILQ_EMPTY(&pci_device_q)) {
+		struct pci_device_info *p = TAILQ_FIRST(&pci_device_q);
+
+		TAILQ_REMOVE(&pci_device_q, p, PCI_DEVICE_Q);
+	}
+
+	pci_scanned = 0;
+}
+
+#ifdef SCAN_PCI_TEST
+static void
+scan_pci_test(void)
+{
+	struct pci_device_info *device_info;
+	struct pci_device *pdev;
+	int bdf, parent_bdf;
+
+	printf("%s enter.\n", __func__);
+	if (!pci_scanned) {
+		printf("%s: no pci hierarchy to test.\n", __func__);
+		return;
+	}
+
+	TAILQ_FOREACH(device_info, &pci_device_q, PCI_DEVICE_Q) {
+		bdf = device_info->bdf;
+
+		if (bdf == 0) {
+			printf("%s: host bridge.\n", __func__);
+			continue;
+		}
+
+		parent_bdf = device_info->parent->bdf;
+
+		printf("%s: [%x:%x.%x]: [%x:%x.%x]\n", __func__, (bdf >> 8) & 0xFF, (bdf >> 3) & 0x1F, bdf & 0x7,
+			(parent_bdf >> 8) & 0xFF, (parent_bdf >> 3) & 0x1F, parent_bdf & 0x7);
+
+		pdev = pci_device_find_by_slot(0, (bdf >> 8) & 0xFF, (bdf >> 3) & 0x1F, bdf & 0x7);
+
+		if (is_bridge(pdev)) {
+			struct pci_device_info *child;
+			child = device_info->clist;
+			while(child != NULL) {
+				printf("\t\t: child: [%x:%x.%x]\n", (child->bdf >> 8) & 0xFF, (child->bdf >> 3) & 0x1F, child->bdf & 0x7);
+				child = child->clist;
+			}
+		}
+	}
+}
+#endif
diff --git a/devicemodel/include/pci_util.h b/devicemodel/include/pci_util.h
index 71cc8a2dc..9be322e45 100644
--- a/devicemodel/include/pci_util.h
+++ b/devicemodel/include/pci_util.h
@@ -11,10 +11,18 @@
 #include <stdbool.h>
 #include "pciaccess.h"
 
+struct pci_device_info;
+
 int pci_find_cap(struct pci_device *pdev, const int cap_id);
 int pci_find_ext_cap(struct pci_device *pdev, int cap_id);
 int pci_get_pcie_type(struct pci_device *dev);
 bool is_root_port(struct pci_device *pdev);
 bool is_bridge(struct pci_device *pdev);
 
+int get_device_count_on_bus(int bus);
+int get_device_count_on_bridge(const struct pci_device_info *bridge_info);
+int scan_pci(void);
+struct pci_device * pci_find_root_port(const struct pci_device *pdev);
+void clean_pci_cache(void);
+
 #endif