Theoretically, in the current codebase, two independent net_devices can
be connected to the same GDM port so we need to check the GDM port is not
used by any other running net_device before setting the forward
configuration to FE_PSE_PORT_DROP.
Moreover, always set in GDM_LONG_LEN_MASK field of REG_GDM_LEN_CFG
register the maximum MTU of all running net_devices connected to the same
GDM port.

Tested-by: Xuegang Lu <xuegang.lu@airoha.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/ethernet/airoha/airoha_eth.c | 59 +++++++++++++++++++++++++-------
 drivers/net/ethernet/airoha/airoha_eth.h |  1 +
 2 files changed, 48 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
index 1d088d95d5fb..44b77a5cc4c5 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.c
+++ b/drivers/net/ethernet/airoha/airoha_eth.c
@@ -1720,8 +1720,8 @@ static int airoha_dev_open(struct net_device *netdev)
 	int err, len = ETH_HLEN + netdev->mtu + ETH_FCS_LEN;
 	struct airoha_gdm_dev *dev = netdev_priv(netdev);
 	struct airoha_gdm_port *port = dev->port;
+	u32 cur_len, pse_port = FE_PSE_PORT_PPE1;
 	struct airoha_qdma *qdma = dev->qdma;
-	u32 pse_port = FE_PSE_PORT_PPE1;
 
 	netif_tx_start_all_queues(netdev);
 	err = airoha_set_vip_for_gdm_port(dev, true);
@@ -1735,10 +1735,20 @@ static int airoha_dev_open(struct net_device *netdev)
 		airoha_fe_clear(qdma->eth, REG_GDM_INGRESS_CFG(port->id),
 				GDM_STAG_EN_MASK);
 
-	airoha_fe_rmw(qdma->eth, REG_GDM_LEN_CFG(port->id),
-		      GDM_SHORT_LEN_MASK | GDM_LONG_LEN_MASK,
-		      FIELD_PREP(GDM_SHORT_LEN_MASK, 60) |
-		      FIELD_PREP(GDM_LONG_LEN_MASK, len));
+	cur_len = airoha_fe_get(qdma->eth, REG_GDM_LEN_CFG(port->id),
+				GDM_LONG_LEN_MASK);
+	if (!port->users || len > cur_len) {
+		/* Opening a sibling net_device with a larger MTU updates the
+		 * MTU of already running devices. This is required to allow
+		 * multiple net_devices with different MTUs to share the same
+		 * GDM port.
+		 */
+		airoha_fe_rmw(qdma->eth, REG_GDM_LEN_CFG(port->id),
+			      GDM_SHORT_LEN_MASK | GDM_LONG_LEN_MASK,
+			      FIELD_PREP(GDM_SHORT_LEN_MASK, 60) |
+			      FIELD_PREP(GDM_LONG_LEN_MASK, len));
+	}
+	port->users++;
 
 	airoha_qdma_set(qdma, REG_QDMA_GLOBAL_CFG,
 			GLOBAL_CFG_TX_DMA_EN_MASK |
@@ -1754,6 +1764,30 @@ static int airoha_dev_open(struct net_device *netdev)
 	return 0;
 }
 
+static void airoha_set_port_mtu(struct airoha_eth *eth,
+				struct airoha_gdm_port *port)
+{
+	u32 len = 0;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(port->devs); i++) {
+		struct airoha_gdm_dev *dev = port->devs[i];
+		struct net_device *netdev;
+
+		if (!dev)
+			continue;
+
+		netdev = netdev_from_priv(dev);
+		if (netif_running(netdev))
+			len = max_t(u32, len, netdev->mtu);
+	}
+	len += ETH_HLEN + ETH_FCS_LEN;
+
+	airoha_fe_rmw(eth, REG_GDM_LEN_CFG(port->id),
+		      GDM_LONG_LEN_MASK,
+		      FIELD_PREP(GDM_LONG_LEN_MASK, len));
+}
+
 static int airoha_dev_stop(struct net_device *netdev)
 {
 	struct airoha_gdm_dev *dev = netdev_priv(netdev);
@@ -1766,8 +1800,12 @@ static int airoha_dev_stop(struct net_device *netdev)
 	for (i = 0; i < netdev->num_tx_queues; i++)
 		netdev_tx_reset_subqueue(netdev, i);
 
-	airoha_set_gdm_port_fwd_cfg(qdma->eth, REG_GDM_FWD_CFG(port->id),
-				    FE_PSE_PORT_DROP);
+	if (--port->users)
+		airoha_set_port_mtu(dev->eth, port);
+	else
+		airoha_set_gdm_port_fwd_cfg(qdma->eth,
+					    REG_GDM_FWD_CFG(port->id),
+					    FE_PSE_PORT_DROP);
 
 	if (atomic_dec_and_test(&qdma->users)) {
 		airoha_qdma_clear(qdma, REG_QDMA_GLOBAL_CFG,
@@ -1922,13 +1960,10 @@ static int airoha_dev_change_mtu(struct net_device *netdev, int mtu)
 {
 	struct airoha_gdm_dev *dev = netdev_priv(netdev);
 	struct airoha_gdm_port *port = dev->port;
-	u32 len = ETH_HLEN + mtu + ETH_FCS_LEN;
-	struct airoha_eth *eth = dev->eth;
 
-	airoha_fe_rmw(eth, REG_GDM_LEN_CFG(port->id),
-		      GDM_LONG_LEN_MASK,
-		      FIELD_PREP(GDM_LONG_LEN_MASK, len));
 	WRITE_ONCE(netdev->mtu, mtu);
+	if (port->users)
+		airoha_set_port_mtu(dev->eth, port);
 
 	return 0;
 }
diff --git a/drivers/net/ethernet/airoha/airoha_eth.h b/drivers/net/ethernet/airoha/airoha_eth.h
index 92fd81bb9269..666e9246e70e 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.h
+++ b/drivers/net/ethernet/airoha/airoha_eth.h
@@ -554,6 +554,7 @@ struct airoha_gdm_dev {
 struct airoha_gdm_port {
 	struct airoha_gdm_dev *devs[AIROHA_MAX_NUM_GDM_DEVS];
 	int id;
+	int users;
 
 	struct airoha_hw_stats stats;
 

-- 
2.54.0