stmmac_platform.c:
static int stmmac_dt_phy(struct plat_stmmacenet_data *plat,
             struct device_node *np, struct device *dev)
{
... ...
    /* If phy-handle is not specified, check if we have a fixed-phy */
    if (!plat->phy_node && of_phy_is_fixed_link(np)) {
		if ((of_phy_register_fixed_link(np) < 0))
            return -ENODEV;

        dev_dbg(dev, "Found fixed-link subnode\n");
        plat->phy_node = of_node_get(np);
        mdio = false;
    }
... ...
}

stmmac_main.c:
static int stmmac_init_phy(struct net_device *dev)
{
... ...
	if (priv->plat->phy_node) {
		phydev = of_phy_connect(dev, priv->plat->phy_node,
					&stmmac_adjust_link, 0, interface);
... ...
}

/drivers/of/of_mdio.c:
int of_phy_register_fixed_link(struct device_node *np)
{
	struct fixed_phy_status status = {};
	struct device_node *fixed_link_node;
	u32 fixed_link_prop[5];
	const char *managed;
	int link_gpio = -1;

	if (of_property_read_string(np, "managed", &managed) == 0 &&
	    strcmp(managed, "in-band-status") == 0) {
		/* status is zeroed, namely its .link member */
		goto register_phy;
	}

	/* New binding */
	fixed_link_node = of_get_child_by_name(np, "fixed-link");
	if (fixed_link_node) {
		status.link = 1;
		status.duplex = of_property_read_bool(fixed_link_node,
						      "full-duplex");
		if (of_property_read_u32(fixed_link_node, "speed",
					 &status.speed)) {
			of_node_put(fixed_link_node);
			return -EINVAL;
		}
		status.pause = of_property_read_bool(fixed_link_node, "pause");
		status.asym_pause = of_property_read_bool(fixed_link_node,
							  "asym-pause");
		link_gpio = of_get_named_gpio_flags(fixed_link_node,
						    "link-gpios", 0, NULL);
		of_node_put(fixed_link_node);
		if (link_gpio == -EPROBE_DEFER)
			return -EPROBE_DEFER;

		goto register_phy;
	}

	/* Old binding */
	if (of_property_read_u32_array(np, "fixed-link", fixed_link_prop,
				       ARRAY_SIZE(fixed_link_prop)) == 0) {
		status.link = 1;
		status.duplex = fixed_link_prop[1];
		status.speed  = fixed_link_prop[2];
		status.pause  = fixed_link_prop[3];
		status.asym_pause = fixed_link_prop[4];
		goto register_phy;
	}

	return -ENODEV;

register_phy:
	return PTR_ERR_OR_ZERO(fixed_phy_register(PHY_POLL, &status, link_gpio,
						  np));
}
EXPORT_SYMBOL(of_phy_register_fixed_link);

stmmac_platform.c:
int fw_phy_register_fixed_link(struct fwnode_handle *np,
			       struct plat_stmmacenet_data *plat)
{
	struct fixed_phy_status status = {};
	u32 fixed_link_prop[5];
	int size = 5, err;
	int link_gpio = -1;
	struct phy_device *phydev = NULL;

	if (FORCE_FIXED_LINK) {
		status.link = 1;
		status.duplex = DUPLEX_FULL;
		status.speed = SPEED_1000;
		pr_info("force fixed-link busid %d\n", plat->bus_id);
	} else {
		err = fwnode_property_read_u32_array(np, "fixed-link", fixed_link_prop, size);
		if (err) {
			pr_err("----there is no fixed-link property in DSD--\n");
			return 0;
		}
		status.link = 1;
		status.duplex = fixed_link_prop[1];
		status.speed = fixed_link_prop[2];
		status.pause  = fixed_link_prop[3];
		status.asym_pause = fixed_link_prop[4];
	}

	phydev = fixed_phy_register(PHY_POLL, &status, link_gpio, 0);
	if (IS_ERR(phydev)) {
		pr_err("fixed_phy_register failed\n");
		return -1;
	}
	plat->fixedphydev = phydev;
	return 0;
}

stmmac_main.c:
static int stmmac_init_phy(struct net_device *dev)
{
... ...
if (priv->plat->fixedphydev) {
		phydev = priv->plat->fixedphydev;
		if (phy_connect_direct(dev, phydev, &stmmac_adjust_link,
				       interface)) {
			netdev_err(priv->dev, "phy_connect_direct failed\n");
			phydev = NULL;
}
... ...
}