netdev - [PATCH net-next 2/2] net: fec: Set max MTU size to allow the MTU to be changed

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Date:   Sat, 11 Jul 2020 22:32:06 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Chris Healy <cphealy@...il.com>,
        Fugang Duan <fugang.duan@....com>, Andrew Lunn <andrew@...n.ch>
Subject: [PATCH net-next 2/2] net: fec: Set max MTU size to allow the MTU to be changed

The FEC allocates 2K buffers, but looses some of it due to
alignment. It can however support an MTU bigger than the default. This
is particularly interesting when used in combination with Ethernet
switches supporting DSA, which have extra headers. The DSA core will
try to increase the MTU to support these extra headers. If the max
size defaults to that of standard Ethernet we get a warning. By
setting the max to what the driver actually supports, we avoid this
warning.

Signed-off-by: Andrew Lunn <andrew@...n.ch>
---
 drivers/net/ethernet/freescale/fec_main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 9f80a33c5b16..8047dda947f2 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -3710,6 +3710,8 @@ fec_probe(struct platform_device *pdev)
 	fec_enet_clk_enable(ndev, false);
 	pinctrl_pm_select_sleep_state(&pdev->dev);
 
+	ndev->max_mtu = PKT_MAXBUF_SIZE - ETH_HLEN - ETH_FCS_LEN;
+
 	ret = register_netdev(ndev);
 	if (ret)
 		goto failed_register;
-- 
2.27.0.rc2