net: stmmac: Tx coe sw fallback

Add sw fallback of tx checksum calculation for those tx queues that
don't support tx checksum offloading. DW xGMAC IP can be synthesized
such that it can support tx checksum offloading only for a few
initial tx queues. Also as Serge pointed out, for the DW QoS IP, tx
coe can be individually configured for each tx queue.

So when tx coe is enabled, for any tx queue that doesn't support
tx coe with 'coe-unsupported' flag set will have a sw fallback
happen in the driver for tx checksum calculation when any packets to
be transmitted on these tx queues.

Signed-off-by: Rohan G Thomas <rohan.g.thomas@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: rohangt07

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

@@ -4401,6 +4401,16 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	WARN_ON(tx_q->tx_skbuff[first_entry]);
 
 	csum_insertion = (skb->ip_summed == CHECKSUM_PARTIAL);
+	/* DWMAC IPs can be synthesized to support tx coe only for a few tx
+	 * queues. In that case, checksum offloading for those queues that don't
+	 * support tx coe needs to fallback to software checksum calculation.
+	 */
+	if (csum_insertion &&
+	    priv->plat->tx_queues_cfg[queue].coe_unsupported) {
+		if (unlikely(skb_checksum_help(skb)))
+			goto dma_map_err;
+		csum_insertion = !csum_insertion;
+	}
 
 	if (likely(priv->extend_desc))
 		desc = (struct dma_desc *)(tx_q->dma_etx + entry);

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

@@ -276,6 +276,9 @@ static int stmmac_mtl_setup(struct platform_device *pdev,
 			plat->tx_queues_cfg[queue].use_prio = true;
 		}
 
+		plat->tx_queues_cfg[queue].coe_unsupported =
+			of_property_read_bool(q_node, "snps,coe-unsupported");
+
 		queue++;
 	}
 	if (queue != plat->tx_queues_to_use) {

include/linux/stmmac.h

@@ -139,6 +139,7 @@ struct stmmac_rxq_cfg {
 
 struct stmmac_txq_cfg {
 	u32 weight;
+	bool coe_unsupported;
 	u8 mode_to_use;
 	/* Credit Base Shaper parameters */
 	u32 send_slope;