netdev - [PATCH] net: bcmgenet: Fix FCS generation for fragmented skbuffs

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Message-ID: <20231226171907.651412-1-adriancinal1@gmail.com>
Date: Tue, 26 Dec 2023 18:19:07 +0100
From: Adrian Cinal <adriancinal1@...il.com>
To: netdev@...r.kernel.org
Cc: opendmb@...il.com,
	florian.fainelli@...adcom.com,
	bcm-kernel-feedback-list@...adcom.com,
	Adrian Cinal <adriancinal1@...il.com>
Subject: [PATCH] net: bcmgenet: Fix FCS generation for fragmented skbuffs

The flag DMA_TX_APPEND_CRC was written to the first (instead of the last)
DMA descriptor in the TX path, with each descriptor corresponding to a
single skbuff fragment (or the skbuff head). This lead to packets with no
FCS appearing on the wire if the kernel allocated the packet in fragments,
which would always happen when using PACKET_MMAP/TPACKET
(cf. tpacket_fill_skb() in af_packet.c).

Signed-off-by: Adrian Cinal <adriancinal1@...il.com>
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index 1174684a7f23..df4b0e557c76 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -2137,16 +2137,16 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
 		len_stat = (size << DMA_BUFLENGTH_SHIFT) |
 			   (priv->hw_params->qtag_mask << DMA_TX_QTAG_SHIFT);
 
-		/* Note: if we ever change from DMA_TX_APPEND_CRC below we
-		 * will need to restore software padding of "runt" packets
-		 */
 		if (!i) {
-			len_stat |= DMA_TX_APPEND_CRC | DMA_SOP;
+			len_stat |= DMA_SOP;
 			if (skb->ip_summed == CHECKSUM_PARTIAL)
 				len_stat |= DMA_TX_DO_CSUM;
 		}
+		/* Note: if we ever change from DMA_TX_APPEND_CRC below we
+		 * will need to restore software padding of "runt" packets
+		 */
 		if (i == nr_frags)
-			len_stat |= DMA_EOP;
+			len_stat |= DMA_TX_APPEND_CRC | DMA_EOP;
 
 		dmadesc_set(priv, tx_cb_ptr->bd_addr, mapping, len_stat);
 	}
-- 
2.43.0