net: stmmac: set TxQ mode back to DCB after disabling CBS

When disable CBS, mode_to_use parameter is not updated even the operation
mode of Tx Queue is changed to Data Centre Bridging (DCB). Therefore,
when tc_setup_cbs() function is called to re-enable CBS, the operation
mode of Tx Queue remains at DCB, which causing CBS fails to work.

This patch updates the value of mode_to_use parameter to MTL_QUEUE_DCB
after operation mode of Tx Queue is changed to DCB in stmmac_dma_qmode()
callback function.

Fixes: 1f705bc61a ("net: stmmac: Add support for CBS QDISC")
Suggested-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Mohammad Athari Bin Ismail <mohammad.athari.ismail@intel.com>
Signed-off-by: Song, Yoong Siang <yoong.siang.song@intel.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Link: https://lore.kernel.org/r/1612447396-20351-1-git-send-email-yoong.siang.song@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c

@@ -324,7 +324,12 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
 
 		priv->plat->tx_queues_cfg[queue].mode_to_use = MTL_QUEUE_AVB;
 	} else if (!qopt->enable) {
-		return stmmac_dma_qmode(priv, priv->ioaddr, queue, MTL_QUEUE_DCB);
+		ret = stmmac_dma_qmode(priv, priv->ioaddr, queue,
+				       MTL_QUEUE_DCB);
+		if (ret)
+			return ret;
+
+		priv->plat->tx_queues_cfg[queue].mode_to_use = MTL_QUEUE_DCB;
 	}
 
 	/* Port Transmit Rate and Speed Divider */