[PATCH 3/3] net: ethernet: ti: am65-cpsw: Add device tree property to set max MTU

[Sanjuán García, Jorge]

The switch supports ethernet frame sizes between 64 and 2024 bytes
(including VLAN) as stated in the technical reference manual.

This patch adds a new devicetree property so the switch ports can
be configured with an MTU higher than the standar 1500 bytes, making
the max frame length configured on the registers and the max_mtu
advertised on the network device consistent.

Signed-off-by: Jorge Sanjuan Garcia <jorge.sanjuangarcia@xxxxxxxxxx>
---
 drivers/net/ethernet/ti/am65-cpsw-nuss.c | 18 ++++++++++++++----
 drivers/net/ethernet/ti/am65-cpsw-nuss.h |  1 +
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
index a920146d7a60..6a5c8b6e03f4 100644
--- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
+++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
@@ -56,7 +56,7 @@
 #define AM65_CPSW_MAX_PORTS	8
 
 #define AM65_CPSW_MIN_PACKET_SIZE	VLAN_ETH_ZLEN
-#define AM65_CPSW_MAX_PACKET_SIZE	(VLAN_ETH_FRAME_LEN + ETH_FCS_LEN)
+#define AM65_CPSW_MAX_PACKET_SIZE	2024
 
 #define AM65_CPSW_REG_CTL		0x004
 #define AM65_CPSW_REG_STAT_PORT_EN	0x014
@@ -2198,8 +2198,7 @@ am65_cpsw_nuss_init_port_ndev(struct am65_cpsw_common *common, u32 port_idx)
 	eth_hw_addr_set(port->ndev, port->slave.mac_addr);
 
 	port->ndev->min_mtu = AM65_CPSW_MIN_PACKET_SIZE;
-	port->ndev->max_mtu = common->rx_packet_max -
-			      (VLAN_ETH_HLEN + ETH_FCS_LEN);
+	port->ndev->max_mtu = common->max_mtu;
 	port->ndev->hw_features = NETIF_F_SG |
 				  NETIF_F_RXCSUM |
 				  NETIF_F_HW_CSUM |
@@ -2927,8 +2926,19 @@ static int am65_cpsw_nuss_probe(struct platform_device *pdev)
 	if (common->port_num < 1 || common->port_num > AM65_CPSW_MAX_PORTS)
 		return -ENOENT;
 
+	common->max_mtu = VLAN_ETH_DATA_LEN;
+	of_property_read_u32(dev->of_node, "max-frame-size", &common->max_mtu);
+
+	common->rx_packet_max = common->max_mtu + VLAN_ETH_HLEN + ETH_FCS_LEN;
+	if (common->rx_packet_max > AM65_CPSW_MAX_PACKET_SIZE) {
+		common->rx_packet_max = AM65_CPSW_MAX_PACKET_SIZE;
+		common->max_mtu = AM65_CPSW_MAX_PACKET_SIZE -
+				  (VLAN_ETH_HLEN + ETH_FCS_LEN);
+	}
+
+	dev_info(common->dev, "Max RX packet size set to %d\n", common->rx_packet_max);
+
 	common->rx_flow_id_base = -1;
-	common->rx_packet_max = AM65_CPSW_MAX_PACKET_SIZE;
 	init_completion(&common->tdown_complete);
 	common->tx_ch_num = AM65_CPSW_DEFAULT_TX_CHNS;
 	common->pf_p0_rx_ptype_rrobin = false;
diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.h b/drivers/net/ethernet/ti/am65-cpsw-nuss.h
index 141160223d73..3bb0ff94a46a 100644
--- a/drivers/net/ethernet/ti/am65-cpsw-nuss.h
+++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.h
@@ -130,6 +130,7 @@ struct am65_cpsw_common {
 	u32			tx_ch_rate_msk;
 	u32			rx_flow_id_base;
 
+	int			max_mtu;
 	int			rx_packet_max;
 
 	struct am65_cpsw_tx_chn	tx_chns[AM65_CPSW_MAX_TX_QUEUES];
-- 
2.34.1