drm/ttm: make TT creation purely optional v3

We only need the page array when the BO is about to be accessed.

So not only populate, but also create it on demand.

v2: move NULL check into ttm_tt_create()
v3: fix the occurrence in ttm_bo_kmap_ttm as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Link: https://patchwork.freedesktop.org/patch/373182/

drivers/gpu/drm/ttm/ttm_bo.c

@@ -292,12 +292,11 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
 	 */
 
 	if (!(new_man->flags & TTM_MEMTYPE_FLAG_FIXED)) {
-		if (bo->ttm == NULL) {
-			bool zero = !(old_man->flags & TTM_MEMTYPE_FLAG_FIXED);
-			ret = ttm_tt_create(bo, zero);
-			if (ret)
-				goto out_err;
-		}
+		bool zero = !(old_man->flags & TTM_MEMTYPE_FLAG_FIXED);
+
+		ret = ttm_tt_create(bo, zero);
+		if (ret)
+			goto out_err;
 
 		ret = ttm_tt_set_placement_caching(bo->ttm, mem->placement);
 		if (ret)
@@ -660,13 +659,8 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo,
 	placement.num_busy_placement = 0;
 	bdev->driver->evict_flags(bo, &placement);
 
-	if (!placement.num_placement && !placement.num_busy_placement) {
-		ret = ttm_bo_pipeline_gutting(bo);
-		if (ret)
-			return ret;
-
-		return ttm_tt_create(bo, false);
-	}
+	if (!placement.num_placement && !placement.num_busy_placement)
+		return ttm_bo_pipeline_gutting(bo);
 
 	evict_mem = bo->mem;
 	evict_mem.mm_node = NULL;
@@ -1195,13 +1189,8 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
 	/*
 	 * Remove the backing store if no placement is given.
 	 */
-	if (!placement->num_placement && !placement->num_busy_placement) {
-		ret = ttm_bo_pipeline_gutting(bo);
-		if (ret)
-			return ret;
-
-		return ttm_tt_create(bo, false);
-	}
+	if (!placement->num_placement && !placement->num_busy_placement)
+		return ttm_bo_pipeline_gutting(bo);
 
 	/*
 	 * Check whether we need to move buffer.
@@ -1218,14 +1207,6 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
 		ttm_flag_masked(&bo->mem.placement, new_flags,
 				~TTM_PL_MASK_MEMTYPE);
 	}
-	/*
-	 * We might need to add a TTM.
-	 */
-	if (bo->mem.mem_type == TTM_PL_SYSTEM && bo->ttm == NULL) {
-		ret = ttm_tt_create(bo, true);
-		if (ret)
-			return ret;
-	}
 	return 0;
 }
 EXPORT_SYMBOL(ttm_bo_validate);

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -532,12 +532,15 @@ static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
 		.interruptible = false,
 		.no_wait_gpu = false
 	};
-	struct ttm_tt *ttm = bo->ttm;
+	struct ttm_tt *ttm;
 	pgprot_t prot;
 	int ret;
 
-	BUG_ON(!ttm);
+	ret = ttm_tt_create(bo, true);
+	if (ret)
+		return ret;
 
+	ttm = bo->ttm;
 	ret = ttm_tt_populate(ttm, &ctx);
 	if (ret)
 		return ret;

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -349,6 +349,11 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
 
 		};
 
+		if (ttm_tt_create(bo, true)) {
+			ret = VM_FAULT_OOM;
+			goto out_io_unlock;
+		}
+
 		ttm = bo->ttm;
 		if (ttm_tt_populate(bo->ttm, &ctx)) {
 			ret = VM_FAULT_OOM;

drivers/gpu/drm/ttm/ttm_tt.c

@@ -50,6 +50,9 @@ 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;
 
@@ -67,7 +70,6 @@ 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;
 	}