netdev - [PATCH iwl-next v1 8/8] igc: SW pad preemptible frames for correct mCRC calculation

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Message-Id: <20250428060225.1306986-9-faizal.abdul.rahim@linux.intel.com>
Date: Mon, 28 Apr 2025 02:02:25 -0400
From: Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>
To: Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Vladimir Oltean <vladimir.oltean@....com>
Cc: intel-wired-lan@...ts.osuosl.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>,
	Chwee-Lin Choong <chwee.lin.choong@...el.com>
Subject: [PATCH iwl-next v1 8/8] igc: SW pad preemptible frames for correct mCRC calculation

From: Chwee-Lin Choong <chwee.lin.choong@...el.com>

A hardware-padded frame transmitted from the preemptible queue
results in an incorrect mCRC computation by hardware, as the
padding bytes are not included in the mCRC calculation.

To address this, manually pad frames in preemptible queues to a
minimum length of 60 bytes using skb_padto() before transmission.
This ensures that the hardware includes the padding bytes in the
mCRC computation, producing a correct mCRC value.

Signed-off-by: Chwee-Lin Choong <chwee.lin.choong@...el.com>
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 6b14b0d165f0..d495aee58601 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -1685,6 +1685,15 @@ static netdev_tx_t igc_xmit_frame_ring(struct sk_buff *skb,
 	first->tx_flags = tx_flags;
 	first->protocol = protocol;
 
+	/* For preemptible queue, manually pad the skb so that HW includes
+	 * padding bytes in mCRC calculation
+	 */
+	if (tx_ring->preemptible && skb->len < ETH_ZLEN) {
+		if (skb_padto(skb, ETH_ZLEN))
+			goto out_drop;
+		skb_put(skb, ETH_ZLEN - skb->len);
+	}
+
 	tso = igc_tso(tx_ring, first, launch_time, first_flag, &hdr_len);
 	if (tso < 0)
 		goto out_drop;
-- 
2.34.1