[PATCH] bmips: bcm6368-enetsw: Bump max MTU to 1536

[Linus Walleij]

The max MTU for this ethernet switch is 1536 bytes, not 1510 as it is
right now. The available overhead is needed when using the DSA switch with
a cascaded DSA switch, which is something that exist in real products,
in this case the Inteno XG6846.

Before this patch (on the lan1 DSA port in this case):
dsa_slave_change_mtu: master->max_mtu = 9724, dev->max_mtu = 10218, DSA overhead = 8
dsa_slave_change_mtu: master = extsw, dev = lan1
dsa_slave_change_mtu: master->max_mtu = 1510, dev->max_mtu = 9724, DSA overhead = 6
dsa_slave_change_mtu: master = eth0, dev = extsw
dsa_slave_change_mtu new_master_mtu 1514 > mtu_limit 1510
mdio_mux-0.1:00: nonfatal error -34 setting MTU to 1500 on port 0

After this patch the error is gone.

Cc: Álvaro Fernández Rojas <noltari at gmail.com>
Cc: Jonas Gorski <jonas.gorski at gmail.com>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
 .../bmips/files/drivers/net/ethernet/broadcom/bcm6368-enetsw.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/target/linux/bmips/files/drivers/net/ethernet/broadcom/bcm6368-enetsw.c b/target/linux/bmips/files/drivers/net/ethernet/broadcom/bcm6368-enetsw.c
index 321e95dbbb3d..96f4c303a433 100644
--- a/target/linux/bmips/files/drivers/net/ethernet/broadcom/bcm6368-enetsw.c
+++ b/target/linux/bmips/files/drivers/net/ethernet/broadcom/bcm6368-enetsw.c
@@ -24,6 +24,7 @@
 
 /* MTU */
 #define ENETSW_TAG_SIZE			(6 + VLAN_HLEN)
+#define ENETSW_MAX_MTU			1536
 #define ENETSW_MTU_OVERHEAD		(VLAN_ETH_HLEN + VLAN_HLEN + \
 					 ENETSW_TAG_SIZE)
 #define ENETSW_FRAG_SIZE(x)		(SKB_DATA_ALIGN(NET_SKB_PAD + x + \
@@ -1067,7 +1068,7 @@ static int bcm6368_enetsw_probe(struct platform_device *pdev)
 	ndev->netdev_ops = &bcm6368_enetsw_ops;
 	ndev->min_mtu = ETH_ZLEN;
 	ndev->mtu = ETH_DATA_LEN + ENETSW_TAG_SIZE;
-	ndev->max_mtu = ETH_DATA_LEN + ENETSW_TAG_SIZE;
+	ndev->max_mtu = ENETSW_MAX_MTU;
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(6,1,0)
 	netif_napi_add(ndev, &priv->napi, bcm6368_enetsw_poll);
 #else
-- 
2.34.1