bnxt_en: Linearize TX SKB if the fragments exceed the max

JIRA: https://issues.redhat.com/browse/RHEL-76565

commit b91e821
Author: Michael Chan <michael.chan@broadcom.com>
Date:   Fri Mar 21 14:16:39 2025 -0700

    bnxt_en: Linearize TX SKB if the fragments exceed the max

    If skb_shinfo(skb)->nr_frags excceds what the chip can support,
    linearize the SKB and warn once to let the user know.
    net.core.max_skb_frags can be lowered, for example, to avoid the
    issue.

    Fixes: 3948b05 ("net: introduce a config option to tweak MAX_SKB_FRAGS")
    Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
    Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
    Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
    Signed-off-by: Michael Chan <michael.chan@broadcom.com>
    Reviewed-by: Simon Horman <horms@kernel.org>
    Link: https://patch.msgid.link/20250321211639.3812992-3-michael.chan@broadcom.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Shruti Parab <shruti.parab@broadcom.com>

Author: Shruti Parab

drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -485,6 +485,17 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	txr = &bp->tx_ring[bp->tx_ring_map[i]];
 	prod = txr->tx_prod;
 
+#if (MAX_SKB_FRAGS > TX_MAX_FRAGS)
+	if (skb_shinfo(skb)->nr_frags > TX_MAX_FRAGS) {
+		netdev_warn_once(dev, "SKB has too many (%d) fragments, max supported is %d.  SKB will be linearized.\n",
+				 skb_shinfo(skb)->nr_frags, TX_MAX_FRAGS);
+		if (skb_linearize(skb)) {
+			dev_kfree_skb_any(skb);
+			dev_core_stats_tx_dropped_inc(dev);
+			return NETDEV_TX_OK;
+		}
+	}
+#endif
 	free_size = bnxt_tx_avail(bp, txr);
 	if (unlikely(free_size < skb_shinfo(skb)->nr_frags + 2)) {
 		/* We must have raced with NAPI cleanup */

drivers/net/ethernet/broadcom/bnxt/bnxt.h

@@ -84,6 +84,10 @@ struct tx_bd {
 
 #define TX_BD_CNT(n)	(((n) << TX_BD_FLAGS_BD_CNT_SHIFT) & TX_BD_FLAGS_BD_CNT)
 
+#define TX_MAX_BD_CNT	32
+
+#define TX_MAX_FRAGS		(TX_MAX_BD_CNT - 2)
+
 struct tx_bd_ext {
 	__le32 tx_bd_hsize_lflags;
 	#define TX_BD_FLAGS_TCP_UDP_CHKSUM			(1 << 0)