powerpc/pseries/iommu: Add iommu_pseries_alloc_table() helper

Creates a helper to allow allocating a new iommu_table without the need
to reallocate the iommu_group.

This will be helpful for replacing the iommu_table for the new DMA window,
after we remove the old one with iommu_tce_table_put().
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/20210817063929.38701-4-leobras.c@gmail.com

arch/powerpc/platforms/pseries/iommu.c

@@ -53,28 +53,31 @@ enum {
 	DDW_EXT_QUERY_OUT_SIZE = 2
 };
 
-static struct iommu_table_group *iommu_pseries_alloc_group(int node)
+static struct iommu_table *iommu_pseries_alloc_table(int node)
 {
-	struct iommu_table_group *table_group;
 	struct iommu_table *tbl;
 
-	table_group = kzalloc_node(sizeof(struct iommu_table_group), GFP_KERNEL,
-			   node);
-	if (!table_group)
-		return NULL;
-
 	tbl = kzalloc_node(sizeof(struct iommu_table), GFP_KERNEL, node);
 	if (!tbl)
-		goto free_group;
+		return NULL;
 
 	INIT_LIST_HEAD_RCU(&tbl->it_group_list);
 	kref_init(&tbl->it_kref);
+	return tbl;
+}
 
-	table_group->tables[0] = tbl;
+static struct iommu_table_group *iommu_pseries_alloc_group(int node)
+{
+	struct iommu_table_group *table_group;
+
+	table_group = kzalloc_node(sizeof(*table_group), GFP_KERNEL, node);
+	if (!table_group)
+		return NULL;
 
+	table_group->tables[0] = iommu_pseries_alloc_table(node);
+	if (table_group->tables[0])
 		return table_group;
 
-free_group:
 	kfree(table_group);
 	return NULL;
 }