mlxsw: spectrum: qdiscs: Update backlog handling of a child qdiscs

When removing a child qdisc its backlog will be decreased from the parent
backlog. The driver backlog count should do the same.
When the parent changes its configuration, the child might need to clean
its stats. However, the backlog can't be cleaned with the rest of the
stats, because it reflects a momentary value that needs to be synced with
the core, not the history of the qdisc.
Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Reviewed-by: Yuval Mintz <yuvalm@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c

@@ -294,6 +294,12 @@ static int
 mlxsw_sp_qdisc_red_destroy(struct mlxsw_sp_port *mlxsw_sp_port,
 			   struct mlxsw_sp_qdisc *mlxsw_sp_qdisc)
 {
+	struct mlxsw_sp_qdisc *root_qdisc = mlxsw_sp_port->root_qdisc;
+
+	if (root_qdisc != mlxsw_sp_qdisc)
+		root_qdisc->stats_base.backlog -=
+					mlxsw_sp_qdisc->stats_base.backlog;
+
 	return mlxsw_sp_tclass_congestion_disable(mlxsw_sp_port,
 						  mlxsw_sp_qdisc->tclass_num);
 }
@@ -358,6 +364,7 @@ mlxsw_sp_qdisc_red_unoffload(struct mlxsw_sp_port *mlxsw_sp_port,
 	backlog = mlxsw_sp_cells_bytes(mlxsw_sp_port->mlxsw_sp,
 				       mlxsw_sp_qdisc->stats_base.backlog);
 	p->qstats->backlog -= backlog;
+	mlxsw_sp_qdisc->stats_base.backlog = 0;
 }
 
 static int
@@ -512,7 +519,7 @@ mlxsw_sp_qdisc_prio_replace(struct mlxsw_sp_port *mlxsw_sp_port,
 {
 	struct tc_prio_qopt_offload_params *p = params;
 	struct mlxsw_sp_qdisc *child_qdisc;
-	int tclass, i, band;
+	int tclass, i, band, backlog;
 	u8 old_priomap;
 	int err;
 
@@ -533,9 +540,12 @@ mlxsw_sp_qdisc_prio_replace(struct mlxsw_sp_port *mlxsw_sp_port,
 			}
 		}
 		if (old_priomap != child_qdisc->prio_bitmap &&
-		    child_qdisc->ops && child_qdisc->ops->clean_stats)
+		    child_qdisc->ops && child_qdisc->ops->clean_stats) {
+			backlog = child_qdisc->stats_base.backlog;
 			child_qdisc->ops->clean_stats(mlxsw_sp_port,
 						      child_qdisc);
+			child_qdisc->stats_base.backlog = backlog;
+		}
 	}
 
 	return 0;