[PATCH net v3 RESEND 5/6] net: bcmasp: account for offload header in TX short packet padding

[Florian Fainelli]

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
must account for this extra header; otherwise, short frames are sent on
the wire smaller than the minimum Ethernet frame size (ETH_ZLEN +
ETH_FCS_LEN).

Furthermore, small frames with payload in page fragments (such as small
TCP segments with CHECKSUM_PARTIAL) have nr_frags > 0 and were skipping
padding entirely because the padding check was restricted to
nr_frags == 0.

Perform the padding check on skb->len before the descriptor loop using
skb_put_padto(), adding sizeof(struct bcmasp_pkt_offload) to min_size
when checksum offload is enabled, and re-read nr_frags after padding in
case the skb was linearized.

Fixes: 490cb412007d ("net: bcmasp: Add support for ASP2.0 Ethernet controller")
Assisted-by: LLM
Reviewed-by: Justin Chen <justin.chen@xxxxxxxxxxxx>
Signed-off-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
---
 .../net/ethernet/broadcom/asp2/bcmasp_intf.c    | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/asp2/bcmasp_intf.c b/drivers/net/ethernet/broadcom/asp2/bcmasp_intf.c
index 693e8cdfe960..a855e637b6f0 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;
@@ -262,16 +262,21 @@ static netdev_tx_t bcmasp_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (!skb)
 		return NETDEV_TX_OK;
 
+	min_size = ETH_ZLEN + ETH_FCS_LEN;
+	if (csum_hw)
+		min_size += sizeof(struct bcmasp_pkt_offload);
+
+	if (skb->len < min_size) {
+		if (skb_put_padto(skb, min_size))
+			return NETDEV_TX_OK;
+		nr_frags = skb_shinfo(skb)->nr_frags;
+	}
+
 	spb_index = intf->tx_spb_index;
 	valid = intf->tx_spb_dma_valid;
 	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))
-					return NETDEV_TX_OK;
-				size = skb->len;
-			}
 			mapping = dma_map_single(kdev, skb->data, size,
 						 DMA_TO_DEVICE);
 		} else {
-- 
2.34.1