drm/ttm: introduce utility function to free an allocated memory node

Existing core code/drivers call drm_mm_put_block on ttm_mem_reg.mm_node
directly.  Future patches will modify TTM behaviour in such a way that
ttm_mem_reg.mm_node doesn't necessarily belong to drm_mm.

Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Acked-by: Thomas Hellström <thellstrom@vmware.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index cb4cf7e..80d37b4 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -475,11 +475,8 @@
 			list_del_init(&bo->ddestroy);
 			++put_count;
 		}
-		if (bo->mem.mm_node) {
-			drm_mm_put_block(bo->mem.mm_node);
-			bo->mem.mm_node = NULL;
-		}
 		spin_unlock(&glob->lru_lock);
+		ttm_bo_mem_put(bo, &bo->mem);
 
 		atomic_set(&bo->reserved, 0);
 
@@ -621,7 +618,6 @@
 			bool no_wait_reserve, bool no_wait_gpu)
 {
 	struct ttm_bo_device *bdev = bo->bdev;
-	struct ttm_bo_global *glob = bo->glob;
 	struct ttm_mem_reg evict_mem;
 	struct ttm_placement placement;
 	int ret = 0;
@@ -667,12 +663,7 @@
 	if (ret) {
 		if (ret != -ERESTARTSYS)
 			printk(KERN_ERR TTM_PFX "Buffer eviction failed\n");
-		spin_lock(&glob->lru_lock);
-		if (evict_mem.mm_node) {
-			drm_mm_put_block(evict_mem.mm_node);
-			evict_mem.mm_node = NULL;
-		}
-		spin_unlock(&glob->lru_lock);
+		ttm_bo_mem_put(bo, &evict_mem);
 		goto out;
 	}
 	bo->evicted = true;
@@ -769,6 +760,19 @@
 	return 0;
 }
 
+void ttm_bo_mem_put(struct ttm_buffer_object *bo, struct ttm_mem_reg *mem)
+{
+	struct ttm_bo_global *glob = bo->glob;
+
+	if (mem->mm_node) {
+		spin_lock(&glob->lru_lock);
+		drm_mm_put_block(mem->mm_node);
+		spin_unlock(&glob->lru_lock);
+		mem->mm_node = NULL;
+	}
+}
+EXPORT_SYMBOL(ttm_bo_mem_put);
+
 /**
  * Repeatedly evict memory from the LRU for @mem_type until we create enough
  * space, or we've evicted everything and there isn't enough space.