Subject: [net-next PATCH 02/11] net: ravb: Disable IP header RX checksum offloading

From: Paul Barker <[email-masked]>
Date: Mon, 30 Sep 2024 17:08:36 +0100

From: Paul Barker <[email-masked]>

For IPv4 packets, the header checksum will always be checked in software
in the RX path (inet_gro_receive() calls ip_fast_csum() unconditionally)
so there is no advantage in asking the hardware to also calculate this
checksum.

Signed-off-by: Paul Barker <[email-masked]>
---
 drivers/net/ethernet/renesas/ravb.h      |  2 +-
 drivers/net/ethernet/renesas/ravb_main.c | 16 +++++++++-------
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
index 4e1e0a754cd9..98496aa39f3d 100644
--- a/drivers/net/ethernet/renesas/ravb.h
+++ b/drivers/net/ethernet/renesas/ravb.h
@@ -1014,7 +1014,7 @@ enum CSR2_BIT {
 	CSR2_RDHD	= 0x08000000,
 };
 
-#define CSR2_CSUM_ENABLE (CSR2_RIP4 | CSR2_RTCP4 | CSR2_RUDP4 | CSR2_RICMP4)
+#define CSR2_CSUM_ENABLE (CSR2_RTCP4 | CSR2_RUDP4 | CSR2_RICMP4)
 
 #define DBAT_ENTRY_NUM	22
 #define RX_QUEUE_OFFSET	4
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index b53f6062a106..f1b487152555 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -749,13 +749,18 @@ static void ravb_get_tx_tstamp(struct net_device *ndev)
 static void ravb_rx_csum_gbeth(struct sk_buff *skb)
 {
 	struct skb_shared_info *shinfo = skb_shinfo(skb);
-	__wsum csum_ip_hdr, csum_proto;
+	__wsum csum_proto;
 	skb_frag_t *last_frag;
 	u8 *hw_csum;
 
 	/* The hardware checksum status is contained in sizeof(__sum16) * 2 = 4
-	 * bytes appended to packet data. First 2 bytes is ip header checksum
-	 * and last 2 bytes is protocol checksum.
+	 * bytes appended to packet data.
+	 *
+	 * For ipv4, the first 2 bytes are the ip header checksum status. We can
+	 * ignore this as it will always be re-checked in inet_gro_receive().
+	 *
+	 * The last 2 bytes are the protocol checksum status which will be zero
+	 * if the checksum has been validated.
 	 */
 	if (unlikely(skb->len < sizeof(__sum16) * 2))
 		return;
@@ -771,16 +776,13 @@ static void ravb_rx_csum_gbeth(struct sk_buff *skb)
 	hw_csum -= sizeof(__sum16);
 	csum_proto = csum_unfold((__force __sum16)get_unaligned_le16(hw_csum));
 
-	hw_csum -= sizeof(__sum16);
-	csum_ip_hdr = csum_unfold((__force __sum16)get_unaligned_le16(hw_csum));
-
 	if (skb_is_nonlinear(skb))
 		skb_frag_size_sub(last_frag, 2 * sizeof(__sum16));
 	else
 		skb_trim(skb, skb->len - 2 * sizeof(__sum16));
 
 	/* TODO: IPV6 Rx checksum */
-	if (skb->protocol == htons(ETH_P_IP) && !csum_ip_hdr && !csum_proto)
+	if (skb->protocol == htons(ETH_P_IP) && !csum_proto)
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
 }
 
-- 
2.43.0