GMAC网卡Fixed-Link模式
fixed-link固定链接模式，mac与对端的连接方式是写死的，通常用于mac to mac（不排除mac to phy的情况）。内核要支持fixed-link模式，需要打开CONFIG_FIXED_PHY配置。
社区版linux的gmac网卡platform平台驱动中，在设备树默认下支持fixed-link，gmac网卡platform平台驱动默认不支持ACPI模式。
fixed-link模式的实现，概括起来就两步，
-
通过
fixed_phy_register创建phy device - 连接phy device
fixed-link的link状态通常是固定的，但也可以通过gpio GPIOF_DIR_IN寄存器获取。
设备树Fixed-Link实现
以4.19.90内核版本为例其实现方式如下（内核版本5.3之后使用phylink替代了phy lib，实现接口有所不同）：
设备树配置中定义fixed-link属性
设备树fixed-link配置
stmac驱动实现，of_phy_register_fixed_link函数读取设备树fixed-link属性并通过fixed_phy_register创建phy device，of_phy_connect连接phy device。
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 subnoden");
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);
... ...
}通过of_phy_register_fixed_link函数可知，fixed-link的配置方式不只一种。
/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);ACPI Fixed-Link实现
本质上ACPI和设备树fixed-link实现是一致的，只是部分接口函数不同，ACPI下可以使用phy_connect_direct进行连接（5.3之后的内核版本使用phylink模式，连接函数是phylink_connect_phy）。
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 %dn", 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 failedn");
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 failedn");
phydev = NULL;
}
... ...
}