>From 3574f1730e262154e901da140baca76463d0bc3f Mon Sep 17 00:00:00 2001 From: Vladimir Oltean Date: Thu, 27 Oct 2022 13:59:03 +0300 Subject: [PATCH 2/3] net: ftmac100: report the correct maximum MTU of 1500 The driver uses the MAX_PKT_SIZE (1518) for both MTU reporting and for TX. However, the 2 places do not measure the same thing. On TX, skb->len measures the entire L2 packet length (without FCS, which software does not possess). So the comparison against 1518 there is correct. What is not correct is the reporting of dev->max_mtu as 1518. Since MTU measures L2 *payload* length (excluding L2 overhead) and not total L2 packet length, it means that the correct max_mtu supported by this device is the standard 1500. Anything higher than that will be dropped on RX currently. To fix this, subtract VLAN_ETH_HLEN from MAX_PKT_SIZE when reporting the max_mtu, since that is the difference between L2 payload length and total L2 length as seen by software. Signed-off-by: Vladimir Oltean --- drivers/net/ethernet/faraday/ftmac100.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/net/ethernet/faraday/ftmac100.c b/drivers/net/ethernet/faraday/ftmac100.c index 8013f85fc148..7c571b4515a9 100644 --- a/drivers/net/ethernet/faraday/ftmac100.c +++ b/drivers/net/ethernet/faraday/ftmac100.c @@ -11,6 +11,7 @@ #include #include #include +#include #include #include #include @@ -1070,7 +1071,7 @@ static int ftmac100_probe(struct platform_device *pdev) SET_NETDEV_DEV(netdev, &pdev->dev); netdev->ethtool_ops = &ftmac100_ethtool_ops; netdev->netdev_ops = &ftmac100_netdev_ops; - netdev->max_mtu = MAX_PKT_SIZE; + netdev->max_mtu = MAX_PKT_SIZE - VLAN_ETH_HLEN; err = platform_get_ethdev_address(&pdev->dev, netdev); if (err == -EPROBE_DEFER) -- 2.34.1