drm/vmwgfx: Make the driver work without the dummy resources

In commit 18025378 ("drm/ttm: stop allocating dummy resources during BO creation")
ttm stopped allocating dummy resources but vmwgfx was never ported to
handle it. Make the driver treat null resources as initial creation and
port code to handle null resources in general.

Fixes kernel oops'es on boot with vmwgfx.
Signed-off-by: Zack Rusin <zackr@vmware.com>
Fixes: 18025378 ("drm/ttm: stop allocating dummy resources during BO creation")
Cc: Christian König <christian.koenig@amd.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230210023437.2214816-1-zack@kde.org

drivers/gpu/drm/vmwgfx/vmwgfx_resource.c

@@ -837,7 +837,8 @@ void vmw_query_move_notify(struct ttm_buffer_object *bo,
 	mutex_lock(&dev_priv->binding_mutex);
 
 	/* If BO is being moved from MOB to system memory */
-	if (new_mem->mem_type == TTM_PL_SYSTEM &&
+	if (old_mem &&
+	    new_mem->mem_type == TTM_PL_SYSTEM &&
 	    old_mem->mem_type == VMW_PL_MOB) {
 		struct vmw_fence_obj *fence;
 

drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c

@@ -515,9 +515,13 @@ static int vmw_move(struct ttm_buffer_object *bo,
 		    struct ttm_resource *new_mem,
 		    struct ttm_place *hop)
 {
-	struct ttm_resource_manager *old_man = ttm_manager_type(bo->bdev, bo->resource->mem_type);
-	struct ttm_resource_manager *new_man = ttm_manager_type(bo->bdev, new_mem->mem_type);
-	int ret;
+	struct ttm_resource_manager *new_man;
+	struct ttm_resource_manager *old_man = NULL;
+	int ret = 0;
+
+	new_man = ttm_manager_type(bo->bdev, new_mem->mem_type);
+	if (bo->resource)
+		old_man = ttm_manager_type(bo->bdev, bo->resource->mem_type);
 
 	if (new_man->use_tt && !vmw_memtype_is_system(new_mem->mem_type)) {
 		ret = vmw_ttm_bind(bo->bdev, bo->ttm, new_mem);
@@ -525,9 +529,15 @@ static int vmw_move(struct ttm_buffer_object *bo,
 			return ret;
 	}
 
+	if (!bo->resource || (bo->resource->mem_type == TTM_PL_SYSTEM &&
+			      bo->ttm == NULL)) {
+		ttm_bo_move_null(bo, new_mem);
+		return 0;
+	}
+
 	vmw_move_notify(bo, bo->resource, new_mem);
 
-	if (old_man->use_tt && new_man->use_tt) {
+	if (old_man && old_man->use_tt && new_man->use_tt) {
 		if (vmw_memtype_is_system(bo->resource->mem_type)) {
 			ttm_bo_move_null(bo, new_mem);
 			return 0;