[PATCH net 1/3] net: lan966x: Fix the MTU calculation

[Horatiu Vultur <horatiu.vultur@microchip.com>]

When the MTU was changed, the lan966x didn't take in consideration
the L2 header and the FCS. So the HW was configured with a smaller
value than what was desired. Therefore the correct value to configure
the HW would be new_mtu + ETH_HLEN + ETH_FCS_LEN.
The vlan tag is not considered here, because at the time when the
blamed commit was added, there was no vlan filtering support. The
vlan fix will be part of the next patch.

Fixes: d28d6d2e37d1 ("net: lan966x: add port module support")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
---
 drivers/net/ethernet/microchip/lan966x/lan966x_main.c | 2 +-
 drivers/net/ethernet/microchip/lan966x/lan966x_main.h | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_main.c b/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
index be2fd030cccbe..b3070c3fcad0a 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
@@ -386,7 +386,7 @@ static int lan966x_port_change_mtu(struct net_device *dev, int new_mtu)
 	int old_mtu = dev->mtu;
 	int err;
 
-	lan_wr(DEV_MAC_MAXLEN_CFG_MAX_LEN_SET(new_mtu),
+	lan_wr(DEV_MAC_MAXLEN_CFG_MAX_LEN_SET(LAN966X_HW_MTU(new_mtu)),
 	       lan966x, DEV_MAC_MAXLEN_CFG(port->chip_port));
 	dev->mtu = new_mtu;
 
diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_main.h b/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
index 9656071b8289e..4ec33999e4df6 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
@@ -26,6 +26,8 @@
 #define LAN966X_BUFFER_MEMORY		(160 * 1024)
 #define LAN966X_BUFFER_MIN_SZ		60
 
+#define LAN966X_HW_MTU(mtu)		((mtu) + ETH_HLEN + ETH_FCS_LEN)
+
 #define PGID_AGGR			64
 #define PGID_SRC			80
 #define PGID_ENTRIES			89
-- 
2.38.0