netdev - [PATCH net] stmmac: Revert "stmmac: align RX buffers"

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Date:   Fri, 20 Aug 2021 19:30:02 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     netdev@...r.kernel.org
Cc:     kernel-team@...roid.com, linux-kernel@...r.kernel.org,
        Matteo Croce <mcroce@...ux.microsoft.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>
Subject: [PATCH net] stmmac: Revert "stmmac: align RX buffers"

This reverts commit a955318fe67e ("stmmac: align RX buffers"),
which breaks at least one platform (Nvidia Jetson-X1), causing
packet corruption. This is 100% reproducible, and reverting
the patch results in a working system again.

Given that it is "only" a performance optimisation, let's
return to a known working configuration until we can have a
good understanding of what is happening here.

Cc: Matteo Croce <mcroce@...ux.microsoft.com>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>
Link: https://lore.kernel.org/netdev/871r71azjw.wl-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@...nel.org>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index fcdb1d20389b..43eead726886 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -339,9 +339,9 @@ static inline bool stmmac_xdp_is_enabled(struct stmmac_priv *priv)
 static inline unsigned int stmmac_rx_offset(struct stmmac_priv *priv)
 {
 	if (stmmac_xdp_is_enabled(priv))
-		return XDP_PACKET_HEADROOM + NET_IP_ALIGN;
+		return XDP_PACKET_HEADROOM;
 
-	return NET_SKB_PAD + NET_IP_ALIGN;
+	return 0;
 }
 
 void stmmac_disable_rx_queue(struct stmmac_priv *priv, u32 queue);
-- 
2.30.2