[PATCH net 5/6] net: bcmasp: account for offload header in TX short packet padding

[Florian Fainelli <florian.fainelli@broadcom.com>]

When hardware checksum offload is enabled for an skb,
bcmasp_csum_offload() prepends a struct bcmasp_pkt_offload header
(20 bytes) to the skb via skb_push(). This increases skb->len and
skb_headlen(skb) by sizeof(struct bcmasp_pkt_offload).

Because the hardware descriptor processor strips this offload header
before transmitting the packet on the wire, the wire packet length is
smaller by sizeof(struct bcmasp_pkt_offload). The padding calculation
did not account for this extra header, causing short frames to skip
padding and be sent on the wire smaller than the minimum Ethernet frame
size (ETH_ZLEN + ETH_FCS_LEN).

Add sizeof(struct bcmasp_pkt_offload) to the minimum padding threshold
when hardware checksum offload is enabled.

Fixes: 490cb412007d ("net: bcmasp: Add support for ASP2.0 Ethernet controller")
Assisted-by: LLM
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 drivers/net/ethernet/broadcom/asp2/bcmasp_intf.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/asp2/bcmasp_intf.c b/drivers/net/ethernet/broadcom/asp2/bcmasp_intf.c
index 7a63a592f158..3370cbf1b395 100644
--- a/drivers/net/ethernet/broadcom/asp2/bcmasp_intf.c
+++ b/drivers/net/ethernet/broadcom/asp2/bcmasp_intf.c
@@ -236,7 +236,7 @@ static struct sk_buff *bcmasp_csum_offload(struct net_device *dev,
 static netdev_tx_t bcmasp_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct bcmasp_intf *intf = netdev_priv(dev);
-	unsigned int total_bytes, size;
+	unsigned int total_bytes, size, min_size;
 	int spb_index, nr_frags, i, j;
 	struct bcmasp_tx_cb *txcb;
 	dma_addr_t mapping, valid;
@@ -267,8 +267,12 @@ static netdev_tx_t bcmasp_xmit(struct sk_buff *skb, struct net_device *dev)
 	for (i = 0; i <= nr_frags; i++) {
 		if (!i) {
 			size = skb_headlen(skb);
-			if (!nr_frags && size < (ETH_ZLEN + ETH_FCS_LEN)) {
-				if (skb_put_padto(skb, ETH_ZLEN + ETH_FCS_LEN))
+			min_size = ETH_ZLEN + ETH_FCS_LEN;
+			if (csum_hw)
+				min_size += sizeof(struct bcmasp_pkt_offload);
+
+			if (!nr_frags && size < min_size) {
+				if (skb_put_padto(skb, min_size))
 					return NETDEV_TX_OK;
 				size = skb->len;
 			}
-- 
2.34.1