linux-kernel - [PATCH net] lan743x: trim all 4 bytes of the FCS; not just 2

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Message-Id: <20210305222445.19053-1-george.mccollister@gmail.com>
Date:   Fri,  5 Mar 2021 16:24:45 -0600
From:   George McCollister <george.mccollister@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Bryan Whitehead <bryan.whitehead@...rochip.com>,
        UNGLinuxDriver@...rochip.com,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Sven Van Asbroeck <thesven73@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        George McCollister <george.mccollister@...il.com>
Subject: [PATCH net] lan743x: trim all 4 bytes of the FCS; not just 2

Trim all 4 bytes of the received FCS; not just 2 of them. Leaving 2
bytes of the FCS on the frame breaks DSA tailing tag drivers.

Fixes: a8db76d40e4d ("lan743x: boost performance on cpu archs w/o dma cache snooping")
Signed-off-by: George McCollister <george.mccollister@...il.com>
---
 drivers/net/ethernet/microchip/lan743x_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/microchip/lan743x_main.c b/drivers/net/ethernet/microchip/lan743x_main.c
index 334e99ffe56f..360d16965a5c 100644
--- a/drivers/net/ethernet/microchip/lan743x_main.c
+++ b/drivers/net/ethernet/microchip/lan743x_main.c
@@ -2040,7 +2040,7 @@ lan743x_rx_trim_skb(struct sk_buff *skb, int frame_length)
 		dev_kfree_skb_irq(skb);
 		return NULL;
 	}
-	frame_length = max_t(int, 0, frame_length - RX_HEAD_PADDING - 2);
+	frame_length = max_t(int, 0, frame_length - RX_HEAD_PADDING - 4);
 	if (skb->len > frame_length) {
 		skb->tail -= skb->len - frame_length;
 		skb->len = frame_length;
-- 
2.11.0