drm/ttm: Fix multihop assert on eviction.

Problem:
Under memory pressure when GTT domain is almost full multihop assert
will come up when trying to evict LRU BO from VRAM to SYSTEM.

Fix:
Don't assert on multihop error in evict code but rather do a retry
as we do in ttm_bo_move_buffer
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210622162339.761651-6-andrey.grodzovsky@amd.com

drivers/gpu/drm/ttm/ttm_bo.c

@@ -485,6 +485,31 @@ void ttm_bo_unlock_delayed_workqueue(struct ttm_device *bdev, int resched)
 }
 EXPORT_SYMBOL(ttm_bo_unlock_delayed_workqueue);
 
+static int ttm_bo_bounce_temp_buffer(struct ttm_buffer_object *bo,
+				     struct ttm_resource **mem,
+				     struct ttm_operation_ctx *ctx,
+				     struct ttm_place *hop)
+{
+	struct ttm_placement hop_placement;
+	struct ttm_resource *hop_mem;
+	int ret;
+
+	hop_placement.num_placement = hop_placement.num_busy_placement = 1;
+	hop_placement.placement = hop_placement.busy_placement = hop;
+
+	/* find space in the bounce domain */
+	ret = ttm_bo_mem_space(bo, &hop_placement, &hop_mem, ctx);
+	if (ret)
+		return ret;
+	/* move to the bounce domain */
+	ret = ttm_bo_handle_move_mem(bo, hop_mem, false, ctx, NULL);
+	if (ret) {
+		ttm_resource_free(bo, &hop_mem);
+		return ret;
+	}
+	return 0;
+}
+
 static int ttm_bo_evict(struct ttm_buffer_object *bo,
 			struct ttm_operation_ctx *ctx)
 {
@@ -524,12 +549,17 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo,
 		goto out;
 	}
 
+bounce:
 	ret = ttm_bo_handle_move_mem(bo, evict_mem, true, ctx, &hop);
-	if (unlikely(ret)) {
-		WARN(ret == -EMULTIHOP, "Unexpected multihop in eviction - likely driver bug\n");
-		if (ret != -ERESTARTSYS)
+	if (ret == -EMULTIHOP) {
+		ret = ttm_bo_bounce_temp_buffer(bo, &evict_mem, ctx, &hop);
+		if (ret) {
 			pr_err("Buffer eviction failed\n");
 			ttm_resource_free(bo, &evict_mem);
+			goto out;
+		}
+		/* try and move to final place now. */
+		goto bounce;
 	}
 out:
 	return ret;
@@ -844,31 +874,6 @@ int ttm_bo_mem_space(struct ttm_buffer_object *bo,
 }
 EXPORT_SYMBOL(ttm_bo_mem_space);
 
-static int ttm_bo_bounce_temp_buffer(struct ttm_buffer_object *bo,
-				     struct ttm_resource **mem,
-				     struct ttm_operation_ctx *ctx,
-				     struct ttm_place *hop)
-{
-	struct ttm_placement hop_placement;
-	struct ttm_resource *hop_mem;
-	int ret;
-
-	hop_placement.num_placement = hop_placement.num_busy_placement = 1;
-	hop_placement.placement = hop_placement.busy_placement = hop;
-
-	/* find space in the bounce domain */
-	ret = ttm_bo_mem_space(bo, &hop_placement, &hop_mem, ctx);
-	if (ret)
-		return ret;
-	/* move to the bounce domain */
-	ret = ttm_bo_handle_move_mem(bo, hop_mem, false, ctx, NULL);
-	if (ret) {
-		ttm_resource_free(bo, &hop_mem);
-		return ret;
-	}
-	return 0;
-}
-
 static int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
 			      struct ttm_placement *placement,
 			      struct ttm_operation_ctx *ctx)