netdev - [PATCH net v1] Revert "lan743x: trim all 4 bytes of the FCS; not just 2"

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Date:   Thu,  8 Apr 2021 13:23:53 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Bryan Whitehead <bryan.whitehead@...rochip.com>,
        David S Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        George McCollister <george.mccollister@...il.com>
Cc:     Sven Van Asbroeck <thesven73@...il.com>,
        UNGLinuxDriver@...rochip.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net v1] Revert "lan743x: trim all 4 bytes of the FCS; not just 2"

From: Sven Van Asbroeck <thesven73@...il.com>

This reverts commit 3e21a10fdea3c2e4e4d1b72cb9d720256461af40.

The reverted patch completely breaks all network connectivity on the
lan7430. tcpdump indicates missing bytes when receiving ping
packets from an external host:

host$ ping $lan7430_ip
lan7430$ tcpdump -v
IP truncated-ip - 2 bytes missing! (tos 0x0, ttl 64, id 21715,
    offset 0, flags [DF], proto ICMP (1), length 84)

Fixes: 3e21a10fdea3 ("lan743x: trim all 4 bytes of the FCS; not just 2")
Signed-off-by: Sven Van Asbroeck <thesven73@...il.com>
---

To: Bryan Whitehead <bryan.whitehead@...rochip.com>
To: "David S. Miller" <davem@...emloft.net>
To: Jakub Kicinski <kuba@...nel.org>
To: George McCollister <george.mccollister@...il.com>
Cc: UNGLinuxDriver@...rochip.com
Cc: netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org

 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 1c3e204d727c..dbdfabff3b00 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 - 4);
+	frame_length = max_t(int, 0, frame_length - RX_HEAD_PADDING - 2);
 	if (skb->len > frame_length) {
 		skb->tail -= skb->len - frame_length;
 		skb->len = frame_length;
-- 
2.17.1