Index: sys/compat/linuxkpi/common/src/linux_pci.c
===================================================================
--- sys/compat/linuxkpi/common/src/linux_pci.c
+++ sys/compat/linuxkpi/common/src/linux_pci.c
@@ -410,7 +410,9 @@
 struct linux_dma_obj {
 	void		*vaddr;
 	uint64_t	dma_addr;
-	bus_dmamap_t	dmamap;
+	bus_dmamap_t	dma_map;
+	size_t		dma_length;
+	uint32_t	dma_refcount;
 };
 
 static uma_zone_t linux_dma_trie_zone;
@@ -497,6 +499,7 @@
 {
 	struct linux_dma_priv *priv;
 	struct linux_dma_obj *obj;
+	struct linux_dma_obj *old;
 	int error, nseg;
 	bus_dma_segment_t seg;
 
@@ -505,34 +508,67 @@
 	obj = uma_zalloc(linux_dma_obj_zone, 0);
 
 	DMA_PRIV_LOCK(priv);
-	if (bus_dmamap_create(priv->dmat, 0, &obj->dmamap) != 0) {
+	if (bus_dmamap_create(priv->dmat, 0, &obj->dma_map) != 0) {
 		DMA_PRIV_UNLOCK(priv);
 		uma_zfree(linux_dma_obj_zone, obj);
 		return (0);
 	}
 
 	nseg = -1;
-	if (_bus_dmamap_load_phys(priv->dmat, obj->dmamap, phys, len,
+	if (_bus_dmamap_load_phys(priv->dmat, obj->dma_map, phys, len,
 	    BUS_DMA_NOWAIT, &seg, &nseg) != 0) {
-		bus_dmamap_destroy(priv->dmat, obj->dmamap);
+		bus_dmamap_destroy(priv->dmat, obj->dma_map);
 		DMA_PRIV_UNLOCK(priv);
 		uma_zfree(linux_dma_obj_zone, obj);
 		return (0);
 	}
 
-	KASSERT(++nseg == 1, ("More than one segment (nseg=%d)", nseg));
+	KASSERT(nseg == 0, ("More than one segment (nseg=%d)", nseg + 1));
 	obj->dma_addr = seg.ds_addr;
+	obj->dma_length = seg.ds_len;
+	obj->dma_refcount = 1;
 
+	/* check if there is an existing mapping */
+	old = LINUX_DMA_PCTRIE_LOOKUP(&priv->ptree, obj->dma_addr);
+	if (unlikely(old != NULL)) {
+
+		KASSERT(old->dma_refcount >= 1,
+		    ("Invalid refcount %u", old->dma_refcount));
+
+		/* sanity check refcount */
+		if (unlikely(old->dma_refcount == UINT_MAX)) {
+			goto error_locked;
+		} else if (obj->dma_length > old->dma_length) {
+			/* new mapping is needed */
+			obj->dma_refcount = old->dma_refcount + 1;
+			LINUX_DMA_PCTRIE_REMOVE(&priv->ptree, old->dma_addr);
+			bus_dmamap_unload(priv->dmat, old->dma_map);
+			bus_dmamap_destroy(priv->dmat, old->dma_map);
+			uma_zfree(linux_dma_obj_zone, old);
+		} else {
+			/* old mapping is sufficient */
+			old->dma_refcount++;
+			bus_dmamap_unload(priv->dmat, obj->dma_map);
+			bus_dmamap_destroy(priv->dmat, obj->dma_map);			
+			DMA_PRIV_UNLOCK(priv);
+			uma_zfree(linux_dma_obj_zone, obj);
+			return (old->dma_addr);
+		}
+	}
+
+	/* insert new mapping */
 	error = LINUX_DMA_PCTRIE_INSERT(&priv->ptree, obj);
-	if (error != 0) {
-		bus_dmamap_unload(priv->dmat, obj->dmamap);
-		bus_dmamap_destroy(priv->dmat, obj->dmamap);
-		DMA_PRIV_UNLOCK(priv);
-		uma_zfree(linux_dma_obj_zone, obj);
-		return (0);
-	}
+	if (error != 0)
+		goto error_locked;
 	DMA_PRIV_UNLOCK(priv);
 	return (obj->dma_addr);
+
+error_locked:
+	bus_dmamap_unload(priv->dmat, obj->dma_map);
+	bus_dmamap_destroy(priv->dmat, obj->dma_map);
+	DMA_PRIV_UNLOCK(priv);
+	uma_zfree(linux_dma_obj_zone, obj);
+	return (0);
 }
 
 void
@@ -541,17 +577,30 @@
 	struct linux_dma_priv *priv;
 	struct linux_dma_obj *obj;
 
+	/* check if DMA address is not mapped */
+	if (unlikely(dma_addr == 0))
+		return;
+
 	priv = dev->dma_priv;
 
 	DMA_PRIV_LOCK(priv);
 	obj = LINUX_DMA_PCTRIE_LOOKUP(&priv->ptree, dma_addr);
-	if (obj == NULL) {
+	if (unlikely(obj == NULL)) {
+		pr_debug("linux_dma_unmap: Bad DMA address 0x%zx\n", (size_t)dma_addr);
 		DMA_PRIV_UNLOCK(priv);
 		return;
 	}
+
+	KASSERT(obj->dma_refcount >= 1,
+	    ("Invalid refcount %u", obj->dma_refcount));
+
+	if (--(obj->dma_refcount) != 0) {
+		DMA_PRIV_UNLOCK(priv);
+		return;
+	}
 	LINUX_DMA_PCTRIE_REMOVE(&priv->ptree, dma_addr);
-	bus_dmamap_unload(priv->dmat, obj->dmamap);
-	bus_dmamap_destroy(priv->dmat, obj->dmamap);
+	bus_dmamap_unload(priv->dmat, obj->dma_map);
+	bus_dmamap_destroy(priv->dmat, obj->dma_map);
 	DMA_PRIV_UNLOCK(priv);
 
 	uma_zfree(linux_dma_obj_zone, obj);
@@ -633,15 +682,17 @@
 
 	nseg = -1;
 	DMA_POOL_LOCK(pool);
-	error = _bus_dmamap_load_phys(pool->pool_dmat, obj->dmamap,
+	error = _bus_dmamap_load_phys(pool->pool_dmat, obj->dma_map,
 	    vtophys(obj->vaddr), pool->pool_entry_size, BUS_DMA_NOWAIT,
 	    &seg, &nseg);
 	DMA_POOL_UNLOCK(pool);
 	if (error != 0) {
 		return (error);
 	}
-	KASSERT(++nseg == 1, ("More than one segment (nseg=%d)", nseg));
+	KASSERT(nseg == 0, ("More than one segment (nseg=%d)", nseg + 1));
 	obj->dma_addr = seg.ds_addr;
+	obj->dma_length = seg.ds_len;
+	obj->dma_refcount = 1;
 
 	return (0);
 }
@@ -653,7 +704,7 @@
 	struct dma_pool *pool = arg;
 
 	DMA_POOL_LOCK(pool);
-	bus_dmamap_unload(pool->pool_dmat, obj->dmamap);
+	bus_dmamap_unload(pool->pool_dmat, obj->dma_map);
 	DMA_POOL_UNLOCK(pool);
 }
 
@@ -673,7 +724,7 @@
 			break;
 
 		error = bus_dmamem_alloc(pool->pool_dmat, &obj->vaddr,
-		    BUS_DMA_NOWAIT, &obj->dmamap);
+		    BUS_DMA_NOWAIT, &obj->dma_map);
 		if (error!= 0) {
 			uma_zfree(linux_dma_obj_zone, obj);
 			break;
@@ -696,7 +747,7 @@
 	priv = pool->pool_device->dma_priv;
 	for (i = 0; i < count; i++) {
 		obj = store[i];
-		bus_dmamem_free(pool->pool_dmat, obj->vaddr, obj->dmamap);
+		bus_dmamem_free(pool->pool_dmat, obj->vaddr, obj->dma_map);
 		uma_zfree(linux_dma_obj_zone, obj);
 	}
 }
@@ -776,12 +827,25 @@
 {
 	struct linux_dma_obj *obj;
 
+	/* check if DMA address is not mapped */
+	if (unlikely(dma_addr == 0))
+		return;
+
 	DMA_POOL_LOCK(pool);
 	obj = LINUX_DMA_PCTRIE_LOOKUP(&pool->pool_ptree, dma_addr);
-	if (obj == NULL) {
+	if (unlikely(obj == NULL)) {
+		pr_debug("linux_dma_pool_free: Bad DMA address 0x%zx\n", (size_t)dma_addr);
 		DMA_POOL_UNLOCK(pool);
 		return;
 	}
+
+	KASSERT(obj->dma_refcount >= 1,
+	    ("Invalid refcount %u", obj->dma_refcount));
+
+	if (--(obj->dma_refcount) != 0) {
+		DMA_POOL_UNLOCK(pool);
+		return;
+	}
 	LINUX_DMA_PCTRIE_REMOVE(&pool->pool_ptree, dma_addr);
 	DMA_POOL_UNLOCK(pool);