net: ethernet: ti: cpsw: fix min eth packet size for non-switch use-cases

The CPSW switchdev driver inherited fix from commit 9421c9015047 ("net:
ethernet: ti: cpsw: fix min eth packet size") which changes min TX packet
size to 64bytes (VLAN_ETH_ZLEN, excluding ETH_FCS). It was done to fix HW
packed drop issue when packets are sent from Host to the port with PVID and
un-tagging enabled. Unfortunately this breaks some other non-switch
specific use-cases, like:
- [1] CPSW port as DSA CPU port with DSA-tag applied at the end of the
packet
- [2] Some industrial protocols, which expects min TX packet size 60Bytes
(excluding FCS).

Fix it by configuring min TX packet size depending on driver mode
- 60Bytes (ETH_ZLEN) for multi mac (dual-mac) mode
- 64Bytes (VLAN_ETH_ZLEN) for switch mode
and update it during driver mode change and annotate with
READ_ONCE()/WRITE_ONCE() as it can be read by napi while writing.

[1] https://lore.kernel.org/netdev/20210531124051.GA15218@cephalopod/
[2] https://e2e.ti.com/support/arm/sitara_arm/f/791/t/701669

Cc: [e-mail]
Fixes: ed3525eda4c4 ("net: ethernet: ti: introduce cpsw switchdev based driver part 1 - dual-emac")
Reported-by: Ben Hutchings <[e-mail]>
Signed-off-by: Grygorii Strashko <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/ti/cpsw_new.c

···
 	struct cpdma_chan *txch;
 	int ret, q_idx;
 
-	if (skb_padto(skb, CPSW_MIN_PACKET_SIZE)) {
+	if (skb_put_padto(skb, READ_ONCE(priv->tx_packet_min))) {
 		cpsw_err(priv, tx_err, "packet pad failed\n");
 		ndev->stats.tx_dropped++;
 		return NET_XMIT_DROP;
···
 
 	for (i = 0; i < n; i++) {
 		xdpf = frames[i];
-		if (xdpf->len < CPSW_MIN_PACKET_SIZE)
+		if (xdpf->len < READ_ONCE(priv->tx_packet_min))
 			break;
 
 		if (cpsw_xdp_tx_frame(priv, xdpf, NULL, priv->emac_port))
···
 		priv->dev  = dev;
 		priv->msg_enable = netif_msg_init(debug_level, CPSW_DEBUG);
 		priv->emac_port = i + 1;
+		priv->tx_packet_min = CPSW_MIN_PACKET_SIZE;
 
 		if (is_valid_ether_addr(slave_data->mac_addr)) {
 			ether_addr_copy(priv->mac_addr, slave_data->mac_addr);
···
 
 			priv = netdev_priv(sl_ndev);
 			slave->port_vlan = vlan;
+			WRITE_ONCE(priv->tx_packet_min, CPSW_MIN_PACKET_SIZE_VLAN);
 			if (netif_running(sl_ndev))
 				cpsw_port_add_switch_def_ale_entries(priv,
 								     slave);
···
 
 			priv = netdev_priv(slave->ndev);
 			slave->port_vlan = slave->data->dual_emac_res_vlan;
+			WRITE_ONCE(priv->tx_packet_min, CPSW_MIN_PACKET_SIZE);
 			cpsw_port_add_dual_emac_def_ale_entries(priv, slave);
 		}
 

drivers/net/ethernet/ti/cpsw_priv.h

···
 
 #define CPSW_POLL_WEIGHT	64
 #define CPSW_RX_VLAN_ENCAP_HDR_SIZE		4
-#define CPSW_MIN_PACKET_SIZE	(VLAN_ETH_ZLEN)
+#define CPSW_MIN_PACKET_SIZE_VLAN	(VLAN_ETH_ZLEN)
+#define CPSW_MIN_PACKET_SIZE	(ETH_ZLEN)
 #define CPSW_MAX_PACKET_SIZE	(VLAN_ETH_FRAME_LEN +\
 				 ETH_FCS_LEN +\
 				 CPSW_RX_VLAN_ENCAP_HDR_SIZE)
···
 	u32 emac_port;
 	struct cpsw_common *cpsw;
 	int offload_fwd_mark;
+	u32 tx_packet_min;
 };
 
 #define ndev_to_cpsw(ndev) (((struct cpsw_priv *)netdev_priv(ndev))->cpsw)