drm/ttm: add a weak BO reference to the resource v3

Keep track for which BO a resource was allocated.
This is necessary to move the LRU handling into the resources.

A bit problematic is i915 since it tries to use the resource
interface without a BO which is illegal from the conceptional
point of view.

v2: Document that this is a weak reference and add a workaround for i915
v3: further document that this is protected by ttm_device::lru_lock and
    clarify the i915 workaround
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220124122514.1832-4-christian.koenig@amd.com

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -241,6 +241,11 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 	if (bo->type != ttm_bo_type_sg)
 		fbo->base.base.resv = &fbo->base.base._resv;
 
+	if (fbo->base.resource) {
+		ttm_resource_set_bo(fbo->base.resource, &fbo->base);
+		bo->resource = NULL;
+	}
+
 	dma_resv_init(&fbo->base.base._resv);
 	fbo->base.base.dev = NULL;
 	ret = dma_resv_trylock(&fbo->base.base._resv);
@@ -509,7 +514,6 @@ static int ttm_bo_move_to_ghost(struct ttm_buffer_object *bo,
 		ghost_obj->ttm = NULL;
 	else
 		bo->ttm = NULL;
-	bo->resource = NULL;
 
 	dma_resv_unlock(&ghost_obj->base._resv);
 	ttm_bo_put(ghost_obj);
@@ -637,7 +641,6 @@ int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo)
 	dma_resv_unlock(&ghost->base._resv);
 	ttm_bo_put(ghost);
 	bo->ttm = ttm;
-	bo->resource = NULL;
 	ttm_bo_assign_mem(bo, sys_res);
 	return 0;
 

drivers/gpu/drm/ttm/ttm_resource.c

@@ -49,6 +49,7 @@ void ttm_resource_init(struct ttm_buffer_object *bo,
 	res->bus.offset = 0;
 	res->bus.is_iomem = false;
 	res->bus.caching = ttm_cached;
+	res->bo = bo;
 }
 EXPORT_SYMBOL(ttm_resource_init);
 
@@ -139,6 +140,14 @@ bool ttm_resource_compat(struct ttm_resource *res,
 }
 EXPORT_SYMBOL(ttm_resource_compat);
 
+void ttm_resource_set_bo(struct ttm_resource *res,
+			 struct ttm_buffer_object *bo)
+{
+	spin_lock(&bo->bdev->lru_lock);
+	res->bo = bo;
+	spin_unlock(&bo->bdev->lru_lock);
+}
+
 /**
  * ttm_resource_manager_init
  *

include/drm/ttm/ttm_resource.h

@@ -161,6 +161,7 @@ struct ttm_bus_placement {
  * @mem_type: Resource type of the allocation.
  * @placement: Placement flags.
  * @bus: Placement on io bus accessible to the CPU
+ * @bo: weak reference to the BO, protected by ttm_device::lru_lock
  *
  * Structure indicating the placement and space resources used by a
  * buffer object.
@@ -171,6 +172,7 @@ struct ttm_resource {
 	uint32_t mem_type;
 	uint32_t placement;
 	struct ttm_bus_placement bus;
+	struct ttm_buffer_object *bo;
 };
 
 /**
@@ -271,6 +273,8 @@ int ttm_resource_alloc(struct ttm_buffer_object *bo,
 void ttm_resource_free(struct ttm_buffer_object *bo, struct ttm_resource **res);
 bool ttm_resource_compat(struct ttm_resource *res,
 			 struct ttm_placement *placement);
+void ttm_resource_set_bo(struct ttm_resource *res,
+			 struct ttm_buffer_object *bo);
 
 void ttm_resource_manager_init(struct ttm_resource_manager *man,
 			       struct ttm_device *bdev,