drm/ttm: add ttm_bo_pin()/ttm_bo_unpin() v2

As an alternative to the placement flag add a
pin count to the ttm buffer object.

v2: add dma_resv_assert_help() calls
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Link: https://patchwork.freedesktop.org/patch/391596/?series=81973&rev=1

drivers/gpu/drm/ttm/ttm_bo.c

@@ -115,7 +115,7 @@ static void ttm_bo_add_mem_to_lru(struct ttm_buffer_object *bo,
 	struct ttm_bo_device *bdev = bo->bdev;
 	struct ttm_resource_manager *man;
 
-	if (!list_empty(&bo->lru))
+	if (!list_empty(&bo->lru) || bo->pin_count)
 		return;
 
 	if (mem->placement & TTM_PL_FLAG_NO_EVICT)
@@ -165,7 +165,8 @@ void ttm_bo_move_to_lru_tail(struct ttm_buffer_object *bo,
 	ttm_bo_del_from_lru(bo);
 	ttm_bo_add_mem_to_lru(bo, &bo->mem);
 
-	if (bulk && !(bo->mem.placement & TTM_PL_FLAG_NO_EVICT)) {
+	if (bulk && !(bo->mem.placement & TTM_PL_FLAG_NO_EVICT) &&
+	    !bo->pin_count) {
 		switch (bo->mem.mem_type) {
 		case TTM_PL_TT:
 			ttm_bo_bulk_move_set_pos(&bulk->tt[bo->priority], bo);
@@ -544,8 +545,9 @@ static void ttm_bo_release(struct kref *kref)
 		 * shrinkers, now that they are queued for
 		 * destruction.
 		 */
-		if (bo->mem.placement & TTM_PL_FLAG_NO_EVICT) {
+		if (bo->mem.placement & TTM_PL_FLAG_NO_EVICT || bo->pin_count) {
 			bo->mem.placement &= ~TTM_PL_FLAG_NO_EVICT;
+			bo->pin_count = 0;
 			ttm_bo_del_from_lru(bo);
 			ttm_bo_add_mem_to_lru(bo, &bo->mem);
 		}
@@ -1172,6 +1174,7 @@ int ttm_bo_init_reserved(struct ttm_bo_device *bdev,
 	bo->moving = NULL;
 	bo->mem.placement = TTM_PL_FLAG_CACHED;
 	bo->acc_size = acc_size;
+	bo->pin_count = 0;
 	bo->sg = sg;
 	if (resv) {
 		bo->base.resv = resv;

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -352,7 +352,6 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 		return -ENOMEM;
 
 	fbo->base = *bo;
-	fbo->base.mem.placement |= TTM_PL_FLAG_NO_EVICT;
 
 	ttm_bo_get(bo);
 	fbo->bo = bo;
@@ -372,6 +371,7 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 	kref_init(&fbo->base.kref);
 	fbo->base.destroy = &ttm_transfered_destroy;
 	fbo->base.acc_size = 0;
+	fbo->base.pin_count = 1;
 	if (bo->type != ttm_bo_type_sg)
 		fbo->base.base.resv = &fbo->base.base._resv;
 

include/drm/ttm/ttm_bo_api.h

@@ -153,6 +153,7 @@ struct ttm_buffer_object {
 
 	struct dma_fence *moving;
 	unsigned priority;
+	unsigned pin_count;
 
 	/**
 	 * Special members that are protected by the reserve lock
@@ -607,6 +608,31 @@ static inline bool ttm_bo_uses_embedded_gem_object(struct ttm_buffer_object *bo)
 	return bo->base.dev != NULL;
 }
 
+/**
+ * ttm_bo_pin - Pin the buffer object.
+ * @bo: The buffer object to pin
+ *
+ * Make sure the buffer is not evicted any more during memory pressure.
+ */
+static inline void ttm_bo_pin(struct ttm_buffer_object *bo)
+{
+	dma_resv_assert_held(bo->base.resv);
+	++bo->pin_count;
+}
+
+/**
+ * ttm_bo_unpin - Unpin the buffer object.
+ * @bo: The buffer object to unpin
+ *
+ * Allows the buffer object to be evicted again during memory pressure.
+ */
+static inline void ttm_bo_unpin(struct ttm_buffer_object *bo)
+{
+	dma_resv_assert_held(bo->base.resv);
+	WARN_ON_ONCE(!bo->pin_count);
+	--bo->pin_count;
+}
+
 int ttm_mem_evict_first(struct ttm_bo_device *bdev,
 			struct ttm_resource_manager *man,
 			const struct ttm_place *place,