drm/ttm: revert "drm/ttm: make TT creation purely optional v3"

This reverts commit 2ddef17678.

As it turned out VMWGFX needs a much wider audit to fix this.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200811092400.188124-1-christian.koenig@amd.com

drivers/gpu/drm/ttm/ttm_tt.c

@@ -50,9 +50,6 @@ int ttm_tt_create(struct ttm_buffer_object *bo, bool zero_alloc)
 
 	dma_resv_assert_held(bo->base.resv);
 
-	if (bo->ttm)
-		return 0;
-
 	if (bdev->need_dma32)
 		page_flags |= TTM_PAGE_FLAG_DMA32;
 
@@ -70,6 +67,7 @@ int ttm_tt_create(struct ttm_buffer_object *bo, bool zero_alloc)
 		page_flags |= TTM_PAGE_FLAG_SG;
 		break;
 	default:
+		bo->ttm = NULL;
 		pr_err("Illegal buffer object type\n");
 		return -EINVAL;
 	}