+static int tsnep_mdiobus_read(struct mii_bus *bus, int addr, int regnum)
+{
+	struct tsnep_adapter *adapter = bus->priv;
+	u16 data;
+	int retval;
+
+	if (adapter->loopback)
+		return 0;
+
+	retval = tsnep_read_md(adapter, addr, regnum, &data);
+	if (retval != 0)
+		return retval;

It appears your MDIO bus can only do C22. Please add a test for C45 and return -EOPNOTSUPP.

+static void tsnep_phy_link_status_change(struct net_device *netdev)
+{
+	struct tsnep_adapter *adapter = netdev_priv(netdev);
+	struct phy_device *phydev = netdev->phydev;
+
+	if (adapter->loopback)
+		return;
+
+	if (adapter->gmii2rgmii) {
+		u16 val;
+
+		if (phydev->link && phydev->speed == 1000)
+			val = BMCR_SPEED1000;
+		else
+			val = BMCR_SPEED100;
+		tsnep_write_md(adapter, ECM_GMII2RGMII_ADDR,
+			       ECM_GMII2RGMII_BMCR, val);
+	}

I _think_ this is wrong. They way the PHYs are chained means you
should not need to do this, the xgmiitorgmii_read_status() does it.
Maybe you have the chaining setup wrong?

+static int tsnep_phy_open(struct tsnep_adapter *adapter)
+{
+	__ETHTOOL_DECLARE_LINK_MODE_MASK(mask);
+	struct ethtool_eee ethtool_eee;
+	int retval;
+
+	retval = phy_connect_direct(adapter->netdev, adapter->phydev,
+				    tsnep_phy_link_status_change,
+				    adapter->phy_mode);
+	if (retval)
+		return -EIO;

phy_connect_direct() returns an error code. Use it, rather than
changing it to something else. This applies everywhere. You must have
a good reason to change error codes, and then it is wise to put a
comment why you change it.

+
+	/* MAC supports only 100Mbps|1000Mbps full duplex
+	 * SPE (Single Pair Ethernet) is also an option but not implemented yet
+	 */
+	linkmode_zero(mask);
+	linkmode_set_bit(ETHTOOL_LINK_MODE_Autoneg_BIT, mask);
+	linkmode_set_bit(ETHTOOL_LINK_MODE_100baseT_Full_BIT, mask);
+	linkmode_set_bit(ETHTOOL_LINK_MODE_1000baseT_Full_BIT, mask);
+	linkmode_and(mask, adapter->phydev->supported, mask);
+	linkmode_copy(adapter->phydev->supported, mask);
+	linkmode_copy(adapter->phydev->advertising, mask);

You should not be accessing the phydev directly. Use
phy_remove_link_mode(phydev, ETHTOOL_LINK_MODE_1000baseT_Half_BIT),
etc.

+static int tsnep_phy_init(struct tsnep_adapter *adapter)
+{
+	struct device_node *dn;
+	u16 val;
+	u32 id;
+	int retval;
+
+	retval = of_get_phy_mode(adapter->pdev->dev.of_node,
+				 &adapter->phy_mode);
+	if (retval)
+		adapter->phy_mode = PHY_INTERFACE_MODE_GMII;
+
+	dn = of_parse_phandle(adapter->pdev->dev.of_node, "phy-handle", 0);
+	adapter->phydev = of_phy_find_device(dn);
+	if (!adapter->phydev)
+		adapter->phydev = phy_find_first(adapter->mdiobus);
+	if (!adapter->phydev)
+		return -EIO;
+
+	/* detect optional GMII2RGMII */
+	retval = tsnep_read_md(adapter, ECM_GMII2RGMII_ADDR, MII_PHYSID1, &val);
+	if (retval)
+		return retval;
+	id = val << 16;
+	retval = tsnep_read_md(adapter, ECM_GMII2RGMII_ADDR, MII_PHYSID2, &val);
+	if (retval)
+		return retval;
+	id |= val;
+	if (id == 0)
+		adapter->gmii2rgmii = true;

This is where i think GMII2RGMII goes wrong. MAC phy-handle should
point to the GMII2RGMII device in DT. The GMII2RGMII should have a
phy-handle which points to the PHY.

+	/* reset PHY */
+	retval = tsnep_write_md(adapter, adapter->phydev->mdio.addr, MII_BMCR,
+				BMCR_RESET);
+	if (retval)
+		return retval;
+
+	/* reset GMII2RGMII */
+	if (adapter->gmii2rgmii) {
+		retval = tsnep_write_md(adapter, ECM_GMII2RGMII_ADDR,
+					ECM_GMII2RGMII_BMCR, BMCR_RESET);
+		if (retval)
+			return retval;
+		retval = tsnep_write_md(adapter, ECM_GMII2RGMII_ADDR,
+					ECM_GMII2RGMII_BMCR, BMCR_SPEED100);
+		if (retval)
+			return retval;
+	}

The PHY driver is in control of the PHY, not the MAC. Please remove.

    Andrew