报错：ethernet eth0: Could not attach to PHY
ethernet eth0: stmmac_open: Cannot attach to PHY (error: -19)
分析：
打印来源于：
- drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
- 945
- 946/**
- 947 * stmmac_init_phy - PHY initialization
- 948 * @dev: net device structure
- 949 * Description: it initializes the driver's PHY state, and attaches the PHY
- 950 * to the mac driver.
- 951 * Return value:
- 952 * 0 on success
- 953 */
- 954static int stmmac_init_phy(struct net_device *dev)
- 955{
- ------------------------------------
- 967 if (priv->plat->phy_node) {
- 968 phydev = of_phy_connect(dev, priv->plat->phy_node,
- 969 &stmmac_adjust_link, 0, interface);
- 970 } else {
- 971 snprintf(bus_id, MII_BUS_ID_SIZE, "stmmac-%x",
- 972 priv->plat->bus_id);
- 973
- 974 snprintf(phy_id_fmt, MII_BUS_ID_SIZE + 3, PHY_ID_FMT, bus_id,
- 975