drm/amdgpu: add optional fence out-parameter to amdgpu_vm_clear_freed

We will add the fence to freed buffer objects in a later commit, to ensure
that the underlying memory can only be re-used after all references in
page tables have been cleared.

Signed-off-by: Nicolai Hähnle <[e-mail]>
Reviewed-by: Chunming Zhou <[e-mail]>
Reviewed-by: Junwei Zhang <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

···
 	if (r)
 		return r;
 
-	r = amdgpu_vm_clear_freed(adev, vm);
+	r = amdgpu_vm_clear_freed(adev, vm, NULL);
 	if (r)
 		return r;
 

drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c

···
 	if (r)
 		goto error;
 
-	r = amdgpu_vm_clear_freed(adev, vm);
+	r = amdgpu_vm_clear_freed(adev, vm, NULL);
 	if (r)
 		goto error;
 

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c

···
  *
  * @adev: amdgpu_device pointer
  * @vm: requested vm
+ * @fence: optional resulting fence (unchanged if no work needed to be done
+ * or if an error occurred)
  *
  * Make sure all freed BOs are cleared in the PT.
  * Returns 0 for success.
···
  * PTs have to be reserved and mutex must be locked!
  */
 int amdgpu_vm_clear_freed(struct amdgpu_device *adev,
-			  struct amdgpu_vm *vm)
+			  struct amdgpu_vm *vm,
+			  struct dma_fence **fence)
 {
 	struct amdgpu_bo_va_mapping *mapping;
-	struct dma_fence *fence = NULL;
+	struct dma_fence *f = NULL;
 	int r;
 
 	while (!list_empty(&vm->freed)) {
···
 		list_del(&mapping->list);
 
 		r = amdgpu_vm_bo_split_mapping(adev, NULL, 0, NULL, vm, mapping,
-					       0, 0, &fence);
-		amdgpu_vm_free_mapping(adev, vm, mapping, fence);
+					       0, 0, &f);
+		amdgpu_vm_free_mapping(adev, vm, mapping, f);
 		if (r) {
-			dma_fence_put(fence);
+			dma_fence_put(f);
 			return r;
 		}
-
 	}
-	dma_fence_put(fence);
+
+	if (fence && f) {
+		dma_fence_put(*fence);
+		*fence = f;
+	} else {
+		dma_fence_put(f);
+	}
+
 	return 0;
 
 }

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h

···
 int amdgpu_vm_update_page_directory(struct amdgpu_device *adev,
 				    struct amdgpu_vm *vm);
 int amdgpu_vm_clear_freed(struct amdgpu_device *adev,
-			  struct amdgpu_vm *vm);
+			  struct amdgpu_vm *vm,
+			  struct dma_fence **fence);
 int amdgpu_vm_clear_invalids(struct amdgpu_device *adev, struct amdgpu_vm *vm,
 			     struct amdgpu_sync *sync);
 int amdgpu_vm_bo_update(struct amdgpu_device *adev,