[PATCH 03/12] drm/ttm: add a weak BO reference to the resource v3

[Christian König]

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 at amd.com>
---
 drivers/gpu/drm/i915/intel_region_ttm.c | 22 ++++++++++++----------
 drivers/gpu/drm/ttm/ttm_bo_util.c       |  7 +++++--
 drivers/gpu/drm/ttm/ttm_resource.c      |  9 +++++++++
 include/drm/ttm/ttm_resource.h          |  4 ++++
 4 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_region_ttm.c b/drivers/gpu/drm/i915/intel_region_ttm.c
index 27fe0668d094..1b2a61b085f7 100644
--- a/drivers/gpu/drm/i915/intel_region_ttm.c
+++ b/drivers/gpu/drm/i915/intel_region_ttm.c
@@ -75,24 +75,26 @@ intel_region_ttm_node_reserve(struct intel_memory_region *mem,
 	int ret;
 
 	/*
-	 * Having to use a mock_bo is unfortunate but stems from some
-	 * drivers having private managers that insist to know what the
-	 * allocate memory is intended for, using it to send private
-	 * data to the manager. Also recently the bo has been used to send
-	 * alignment info to the manager. Assume that apart from the latter,
-	 * none of the managers we use will ever access the buffer object
-	 * members, hoping we can pass the alignment info in the
-	 * struct ttm_place in the future.
+	 * This is essential an illegal use the of the TTM resource manager
+	 * backend and should be fixed in the future. For now work around by
+	 * using a mock_bo with at least the mandatory fields initialized.
+	 *
+	 * The resource should be ignored by TTM since it can't grab a
+	 * reference to the BO during eviction.
 	 */
 
 	place.fpfn = offset >> PAGE_SHIFT;
 	place.lpfn = place.fpfn + (size >> PAGE_SHIFT);
 	mock_bo.base.size = size;
+	mock_bo.bdev = &mem->i915->bdev;
 	ret = man->func->alloc(man, &mock_bo, &place, &res);
 	if (ret == -ENOSPC)
-		ret = -ENXIO;
+		return ERR_PTR(-ENXIO);
+	if (ret)
+		return ERR_PTR(ret);
 
-	return ret ? ERR_PTR(ret) : res;
+	res->bo = NULL;
+	return 0;
 }
 
 /**
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 763fa6f4e07d..c5d02edaefc0 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -242,6 +242,11 @@ 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);
@@ -510,7 +515,6 @@ 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);
@@ -638,7 +642,6 @@ 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;
 
diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
index 122f19e6968b..a4c495da0040 100644
--- a/drivers/gpu/drm/ttm/ttm_resource.c
+++ b/drivers/gpu/drm/ttm/ttm_resource.c
@@ -41,6 +41,7 @@ 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);
 
@@ -73,6 +74,14 @@ void ttm_resource_free(struct ttm_buffer_object *bo, struct ttm_resource **res)
 }
 EXPORT_SYMBOL(ttm_resource_free);
 
+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
  *
diff --git a/include/drm/ttm/ttm_resource.h b/include/drm/ttm/ttm_resource.h
index c004672789b6..e8080192cae4 100644
--- a/include/drm/ttm/ttm_resource.h
+++ b/include/drm/ttm/ttm_resource.h
@@ -160,6 +160,7 @@ 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.
@@ -170,6 +171,7 @@ struct ttm_resource {
 	uint32_t mem_type;
 	uint32_t placement;
 	struct ttm_bus_placement bus;
+	struct ttm_buffer_object *bo;
 };
 
 /**
@@ -268,6 +270,8 @@ int ttm_resource_alloc(struct ttm_buffer_object *bo,
 		       const struct ttm_place *place,
 		       struct ttm_resource **res);
 void ttm_resource_free(struct ttm_buffer_object *bo, struct ttm_resource **res);
+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,
-- 
2.25.1