drm/gem-vram: handle NULL bo->resource in move callback

The ttm BO now initially has NULL bo->resource, and leaves the driver
the handle that. However it looks like we forgot to handle that for
ttm_bo_move_memcpy() users, like with vram-gem, since it just silently
returns zero. This seems to then trigger warnings like:

WARNING: CPU: 0 PID: 1 at drivers/gpu/drm/drm_gem_vram_helper.c:255 drm_gem_vram_offset (??:?)

Fix this by calling move_null() if the new resource is TTM_PL_SYSTEM,
otherwise do the multi-hop sequence to ensure can safely call into
ttm_bo_move_memcpy(), since it might also need to clear the memory.
This should give the same behaviour as before.

While we are here let's also treat calling ttm_bo_move_memcpy() with
NULL bo->resource as programmer error, where expectation is that upper
layers should now handle it.

Fixes: 18025378 ("drm/ttm: stop allocating dummy resources during BO creation")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230208145319.397235-1-matthew.auld@intel.comAcked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/drm_gem_vram_helper.c

@@ -916,6 +916,17 @@ static int bo_driver_move(struct ttm_buffer_object *bo,
 {
 	struct drm_gem_vram_object *gbo;
 
+	if (!bo->resource) {
+		if (new_mem->mem_type != TTM_PL_SYSTEM) {
+			hop->mem_type = TTM_PL_SYSTEM;
+			hop->flags = TTM_PL_FLAG_TEMPORARY;
+			return -EMULTIHOP;
+		}
+
+		ttm_bo_move_null(bo, new_mem);
+		return 0;
+	}
+
 	gbo = drm_gem_vram_of_bo(bo);
 
 	return drm_gem_vram_bo_driver_move(gbo, evict, ctx, new_mem);

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -157,8 +157,8 @@ int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
 	bool clear;
 	int ret = 0;
 
-	if (!src_mem)
-		return 0;
+	if (WARN_ON(!src_mem))
+		return -EINVAL;
 
 	src_man = ttm_manager_type(bdev, src_mem->mem_type);
 	if (ttm && ((ttm->page_flags & TTM_TT_FLAG_SWAPPED) ||