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

[Thomas Hellström]

On 11/24/21 13:44, Christian König wrote:
> 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.

s/conceptional/conceptual/ ?

Can't find the i915 workaround below? Was this the mock bo that was used 
in the selftest code, perhaps that was replaced with allowing 
resource->bo to be NULL. In that case the commit message should be updated.

/Thomas.


>
> 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/ttm/ttm_bo_util.c  | 7 +++++--
>   drivers/gpu/drm/ttm/ttm_resource.c | 9 +++++++++
>   include/drm/ttm/ttm_resource.h     | 4 ++++
>   3 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 95de2691ee7c..a2e3a9626198 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -237,6 +237,11 @@ 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);
> @@ -512,7 +517,6 @@ 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;
>   
> diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
> index 41e7bf195168..7fdd58b53c61 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);
>   
> @@ -122,6 +123,14 @@ 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
>    *
> diff --git a/include/drm/ttm/ttm_resource.h b/include/drm/ttm/ttm_resource.h
> index 6bf37383002b..69eea9d6399b 100644
> --- a/include/drm/ttm/ttm_resource.h
> +++ b/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,