netdev - [PATCH net 1/2] bnxt_en: Mask the bd_cnt field in the TX BD properly

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Message-ID: <20250321211639.3812992-2-michael.chan@broadcom.com>
Date: Fri, 21 Mar 2025 14:16:38 -0700
From: Michael Chan <michael.chan@...adcom.com>
To: davem@...emloft.net
Cc: netdev@...r.kernel.org,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	andrew+netdev@...n.ch,
	pavan.chebbi@...adcom.com,
	andrew.gospodarek@...adcom.com,
	osk@...gle.com,
	Kalesh AP <kalesh-anakkur.purayil@...adcom.com>,
	Somnath Kotur <somnath.kotur@...adcom.com>
Subject: [PATCH net 1/2] bnxt_en: Mask the bd_cnt field in the TX BD properly

The bd_cnt field in the TX BD specifies the total number of BDs for
the TX packet.  The bd_cnt field has 5 bits and the maximum number
supported is 32 with the value 0.

CONFIG_MAX_SKB_FRAGS can be modified and the total number of SKB
fragments can approach or exceed the maximum supported by the chip.
Add a macro to properly mask the bd_cnt field so that the value 32
will be properly masked and set to 0 in the bd_cnd field.

Without this patch, the out-of-range bd_cnt value will corrupt the
TX BD and may cause TX timeout.

The next patch will check for values exceeding 32.

Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAGS")
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@...adcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@...adcom.com>
Reviewed-by: Andy Gospodarek <andrew.gospodarek@...adcom.com>
Signed-off-by: Michael Chan <michael.chan@...adcom.com>
---
 drivers/net/ethernet/broadcom/bnxt/bnxt.c     | 4 ++--
 drivers/net/ethernet/broadcom/bnxt/bnxt.h     | 2 ++
 drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c | 3 +--
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
index 0ddc3d41e2d8..158e9789c1f4 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
@@ -564,7 +564,7 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
 					TX_BD_FLAGS_LHINT_512_AND_SMALLER |
 					TX_BD_FLAGS_COAL_NOW |
 					TX_BD_FLAGS_PACKET_END |
-					(2 << TX_BD_FLAGS_BD_CNT_SHIFT));
+					TX_BD_CNT(2));
 
 		if (skb->ip_summed == CHECKSUM_PARTIAL)
 			tx_push1->tx_bd_hsize_lflags =
@@ -639,7 +639,7 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	dma_unmap_addr_set(tx_buf, mapping, mapping);
 	flags = (len << TX_BD_LEN_SHIFT) | TX_BD_TYPE_LONG_TX_BD |
-		((last_frag + 2) << TX_BD_FLAGS_BD_CNT_SHIFT);
+		TX_BD_CNT(last_frag + 2);
 
 	txbd->tx_bd_haddr = cpu_to_le64(mapping);
 	txbd->tx_bd_opaque = SET_TX_OPAQUE(bp, txr, prod, 2 + last_frag);
diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.h b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
index 2373f423a523..3b4a044db73e 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.h
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
@@ -82,6 +82,8 @@ struct tx_bd {
 #define TX_OPAQUE_PROD(bp, opq)	((TX_OPAQUE_IDX(opq) + TX_OPAQUE_BDS(opq)) &\
 				 (bp)->tx_ring_mask)
 
+#define TX_BD_CNT(n)	(((n) << TX_BD_FLAGS_BD_CNT_SHIFT) & TX_BD_FLAGS_BD_CNT)
+
 struct tx_bd_ext {
 	__le32 tx_bd_hsize_lflags;
 	#define TX_BD_FLAGS_TCP_UDP_CHKSUM			(1 << 0)
diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
index 299822cacca4..d71bad3cfd6b 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
@@ -48,8 +48,7 @@ struct bnxt_sw_tx_bd *bnxt_xmit_bd(struct bnxt *bp,
 		tx_buf->page = virt_to_head_page(xdp->data);
 
 	txbd = &txr->tx_desc_ring[TX_RING(bp, prod)][TX_IDX(prod)];
-	flags = (len << TX_BD_LEN_SHIFT) |
-		((num_frags + 1) << TX_BD_FLAGS_BD_CNT_SHIFT) |
+	flags = (len << TX_BD_LEN_SHIFT) | TX_BD_CNT(num_frags + 1) |
 		bnxt_lhint_arr[len >> 9];
 	txbd->tx_bd_len_flags_type = cpu_to_le32(flags);
 	txbd->tx_bd_opaque = SET_TX_OPAQUE(bp, txr, prod, 1 + num_frags);
-- 
2.30.1