net: stmmac: clean all pending Tx buffers during suspend

To ensure driver enters low power state without leaving behind Tx frame
that are in Tx DMA ring but not yet returned through Tx Done operation,
we introduce a function here to clean them.

Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>

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

@@ -6271,6 +6271,37 @@ int stmmac_reinit_ringparam(struct net_device *dev, u32 rx_size, u32 tx_size)
 	return ret;
 }
 
+static void stmmac_clean_tx_queue(struct stmmac_priv *priv,
+				  struct stmmac_tx_queue *tx_q)
+{
+	u32 queue = tx_q->queue_index;
+	unsigned int entry;
+
+	entry = tx_q->dirty_tx;
+	while (entry != tx_q->cur_tx) {
+		/* Free all the Tx ring sk_buffs */
+		stmmac_free_tx_buffer(priv, queue, entry);
+
+		entry = STMMAC_GET_ENTRY(entry, priv->dma_tx_size);
+	}
+	tx_q->dirty_tx = entry;
+
+	/* reset BQL for queue */
+	netdev_tx_reset_queue(netdev_get_tx_queue(priv->dev, queue));
+}
+
+void stmmac_clean_all_tx_rings(struct stmmac_priv *priv)
+{
+	u32 tx_count = priv->plat->tx_queues_to_use;
+	u32 queue;
+
+	for (queue = 0; queue < tx_count; queue++) {
+		struct stmmac_tx_queue *tx_q = get_tx_queue(priv, queue);
+
+		stmmac_clean_tx_queue(priv, tx_q);
+	}
+}
+
 /**
  * stmmac_dvr_probe
  * @device: device pointer
@@ -6764,6 +6795,8 @@ int stmmac_suspend(struct device *dev)
 		stmmac_fpe_set_enable(priv, priv->hw, ndev, false);
 	}
 
+	stmmac_clean_all_tx_rings(priv);
+
 	mutex_unlock(&priv->lock);
 
 	priv->speed = SPEED_UNKNOWN;