ravb: Add Tx checksum offload support for GbEth

TOE has hardware support for calculating IP header and TCP/UDP/ICMP
checksum for both IPv4 and IPv6.

Add Tx checksum offload supported by TOE for IPv4 and TCP/UDP.

For Tx, the result of checksum calculation is set to the checksum field of
each IPv4 Header/TCP/UDP/ICMP of ethernet frames. For the unsupported
frames, those fields are not changed. If a transmission frame is an UDPv4
frame and its checksum value in the UDP header field is 0x0000, TOE does
not calculate checksum for UDP part of this frame as it is optional
function as per standards.

We can test this functionality by the below commands

ethtool -K eth0 tx on --> to turn on Tx checksum offload
ethtool -K eth0 tx off --> to turn off Tx checksum offload
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://lore.kernel.org/r/20240207092838.160627-3-biju.das.jz@bp.renesas.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/renesas/ravb.h

@@ -208,6 +208,7 @@ enum ravb_reg {
 
 	/* TOE registers (RZ/G2L only) */
 	CSR0    = 0x0800,
+	CSR1    = 0x0804,
 	CSR2    = 0x0808,
 };
 
@@ -981,6 +982,20 @@ enum CSR0_BIT {
 	CSR0_RPE	= 0x00000020,
 };
 
+enum CSR1_BIT {
+	CSR1_TIP4	= 0x00000001,
+	CSR1_TTCP4	= 0x00000010,
+	CSR1_TUDP4	= 0x00000020,
+	CSR1_TICMP4	= 0x00000040,
+	CSR1_TTCP6	= 0x00100000,
+	CSR1_TUDP6	= 0x00200000,
+	CSR1_TICMP6	= 0x00400000,
+	CSR1_THOP	= 0x01000000,
+	CSR1_TROUT	= 0x02000000,
+	CSR1_TAHD	= 0x04000000,
+	CSR1_TDHD	= 0x08000000,
+};
+
 enum CSR2_BIT {
 	CSR2_RIP4	= 0x00000001,
 	CSR2_RTCP4	= 0x00000010,

drivers/net/ethernet/renesas/ravb_main.c

@@ -29,6 +29,7 @@
 #include <linux/spinlock.h>
 #include <linux/reset.h>
 #include <linux/math64.h>
+#include <net/ip.h>
 
 #include "ravb.h"
 
@@ -514,16 +515,28 @@ static int ravb_ring_init(struct net_device *ndev, int q)
 
 static void ravb_csum_init_gbeth(struct net_device *ndev)
 {
-	if (!(ndev->features & NETIF_F_RXCSUM))
+	bool tx_enable = ndev->features & NETIF_F_HW_CSUM;
+	bool rx_enable = ndev->features & NETIF_F_RXCSUM;
+
+	if (!(tx_enable || rx_enable))
 		goto done;
 
 	ravb_write(ndev, 0, CSR0);
-	if (ravb_wait(ndev, CSR0, CSR0_RPE, 0)) {
+	if (ravb_wait(ndev, CSR0, CSR0_TPE | CSR0_RPE, 0)) {
 		netdev_err(ndev, "Timeout enabling hardware checksum\n");
-		ndev->features &= ~NETIF_F_RXCSUM;
+
+		if (tx_enable)
+			ndev->features &= ~NETIF_F_HW_CSUM;
+
+		if (rx_enable)
+			ndev->features &= ~NETIF_F_RXCSUM;
 	} else {
-		ravb_write(ndev, CSR2_RIP4 | CSR2_RTCP4 | CSR2_RUDP4 | CSR2_RICMP4,
-			   CSR2);
+		if (tx_enable)
+			ravb_write(ndev, CSR1_TIP4 | CSR1_TTCP4 | CSR1_TUDP4, CSR1);
+
+		if (rx_enable)
+			ravb_write(ndev, CSR2_RIP4 | CSR2_RTCP4 | CSR2_RUDP4 | CSR2_RICMP4,
+				   CSR2);
 	}
 
 done:
@@ -2053,6 +2066,36 @@ static void ravb_tx_timeout_work(struct work_struct *work)
 	rtnl_unlock();
 }
 
+static bool ravb_can_tx_csum_gbeth(struct sk_buff *skb)
+{
+	struct iphdr *ip = ip_hdr(skb);
+
+	/* TODO: Need to add support for VLAN tag 802.1Q */
+	if (skb_vlan_tag_present(skb))
+		return false;
+
+	/* TODO: Need to add hardware checksum for IPv6 */
+	if (skb->protocol != htons(ETH_P_IP))
+		return false;
+
+	switch (ip->protocol) {
+	case IPPROTO_TCP:
+		break;
+	case IPPROTO_UDP:
+		/* If the checksum value in the UDP header field is 0, TOE does
+		 * not calculate checksum for UDP part of this frame as it is
+		 * optional function as per standards.
+		 */
+		if (udp_hdr(skb)->check == 0)
+			return false;
+		break;
+	default:
+		return false;
+	}
+
+	return true;
+}
+
 /* Packet transmit function for Ethernet AVB */
 static netdev_tx_t ravb_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
@@ -2068,6 +2111,9 @@ static netdev_tx_t ravb_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	u32 entry;
 	u32 len;
 
+	if (skb->ip_summed == CHECKSUM_PARTIAL && !ravb_can_tx_csum_gbeth(skb))
+		skb_checksum_help(skb);
+
 	spin_lock_irqsave(&priv->lock, flags);
 	if (priv->cur_tx[q] - priv->dirty_tx[q] > (priv->num_tx_ring[q] - 1) *
 	    num_tx_desc) {
@@ -2473,6 +2519,17 @@ static int ravb_set_features_gbeth(struct net_device *ndev,
 			goto done;
 	}
 
+	if (changed & NETIF_F_HW_CSUM) {
+		if (features & NETIF_F_HW_CSUM)
+			val = CSR1_TIP4 | CSR1_TTCP4 | CSR1_TUDP4;
+		else
+			val = 0;
+
+		ret = ravb_endisable_csum_gbeth(ndev, CSR1, val, CSR0_TPE);
+		if (ret)
+			goto done;
+	}
+
 	ndev->features = features;
 done:
 	spin_unlock_irqrestore(&priv->lock, flags);
@@ -2657,8 +2714,8 @@ static const struct ravb_hw_info gbeth_hw_info = {
 	.emac_init = ravb_emac_init_gbeth,
 	.gstrings_stats = ravb_gstrings_stats_gbeth,
 	.gstrings_size = sizeof(ravb_gstrings_stats_gbeth),
-	.net_hw_features = NETIF_F_RXCSUM,
-	.net_features = NETIF_F_RXCSUM,
+	.net_hw_features = NETIF_F_RXCSUM | NETIF_F_HW_CSUM,
+	.net_features = NETIF_F_RXCSUM | NETIF_F_HW_CSUM,
 	.stats_len = ARRAY_SIZE(ravb_gstrings_stats_gbeth),
 	.max_rx_len = ALIGN(GBETH_RX_BUFF_MAX, RAVB_ALIGN),
 	.tccr_mask = TCCR_TSRQ0,