powerpc/pseries/iommu: Add ddw_list_new_entry() helper

There are two functions creating direct_window_list entries in a
similar way, so create a ddw_list_new_entry() to avoid duplicity and
simplify those functions.
Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210817063929.38701-5-leobras.c@gmail.com

arch/powerpc/platforms/pseries/iommu.c

@@ -874,6 +874,21 @@ static u64 find_existing_ddw(struct device_node *pdn, int *window_shift)
 	return dma_addr;
 }
 
+static struct direct_window *ddw_list_new_entry(struct device_node *pdn,
+						const struct dynamic_dma_window_prop *dma64)
+{
+	struct direct_window *window;
+
+	window = kzalloc(sizeof(*window), GFP_KERNEL);
+	if (!window)
+		return NULL;
+
+	window->device = pdn;
+	window->prop = dma64;
+
+	return window;
+}
+
 static int find_existing_ddw_windows(void)
 {
 	int len;
@@ -886,18 +901,15 @@ static int find_existing_ddw_windows(void)
 
 	for_each_node_with_property(pdn, DIRECT64_PROPNAME) {
 		direct64 = of_get_property(pdn, DIRECT64_PROPNAME, &len);
-		if (!direct64)
-			continue;
-
-		window = kzalloc(sizeof(*window), GFP_KERNEL);
-		if (!window || len < sizeof(struct dynamic_dma_window_prop)) {
-			kfree(window);
+		if (!direct64 || len < sizeof(*direct64)) {
 			remove_ddw(pdn, true);
 			continue;
 		}
 
-		window->device = pdn;
-		window->prop = direct64;
+		window = ddw_list_new_entry(pdn, direct64);
+		if (!window)
+			break;
+
 		spin_lock(&direct_window_list_lock);
 		list_add(&window->list, &direct_window_list);
 		spin_unlock(&direct_window_list_lock);
@@ -1307,7 +1319,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 	dev_dbg(&dev->dev, "created tce table LIOBN 0x%x for %pOF\n",
 		  create.liobn, dn);
 
-	window = kzalloc(sizeof(*window), GFP_KERNEL);
+	window = ddw_list_new_entry(pdn, ddwprop);
 	if (!window)
 		goto out_clear_window;
 
@@ -1326,8 +1338,6 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 		goto out_free_window;
 	}
 
-	window->device = pdn;
-	window->prop = ddwprop;
 	spin_lock(&direct_window_list_lock);
 	list_add(&window->list, &direct_window_list);
 	spin_unlock(&direct_window_list_lock);