net: stmmac: dwmac-qcom-ethqos: add support for the optional serdes phy

On sa8775p platforms, there's a SGMII SerDes PHY between the MAC and
external PHY that we need to enable and configure.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c

@@ -6,6 +6,7 @@
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
 #include <linux/phy.h>
+#include <linux/phy/phy.h>
 #include <linux/property.h>
 
 #include "stmmac.h"
@@ -93,6 +94,7 @@ struct qcom_ethqos {
 
 	unsigned int rgmii_clk_rate;
 	struct clk *rgmii_clk;
+	struct phy *serdes_phy;
 	unsigned int speed;
 
 	const struct ethqos_emac_por *por;
@@ -565,6 +567,30 @@ static void ethqos_fix_mac_speed(void *priv, unsigned int speed)
 	ethqos_configure(ethqos);
 }
 
+static int qcom_ethqos_serdes_powerup(struct net_device *ndev, void *priv)
+{
+	struct qcom_ethqos *ethqos = priv;
+	int ret;
+
+	ret = phy_init(ethqos->serdes_phy);
+	if (ret)
+		return ret;
+
+	ret = phy_power_on(ethqos->serdes_phy);
+	if (ret)
+		return ret;
+
+	return phy_set_speed(ethqos->serdes_phy, ethqos->speed);
+}
+
+static void qcom_ethqos_serdes_powerdown(struct net_device *ndev, void *priv)
+{
+	struct qcom_ethqos *ethqos = priv;
+
+	phy_power_off(ethqos->serdes_phy);
+	phy_exit(ethqos->serdes_phy);
+}
+
 static int ethqos_clks_config(void *priv, bool enabled)
 {
 	struct qcom_ethqos *ethqos = priv;
@@ -650,6 +676,12 @@ static int qcom_ethqos_probe(struct platform_device *pdev)
 	if (ret)
 		goto out_config_dt;
 
+	ethqos->serdes_phy = devm_phy_optional_get(dev, "serdes");
+	if (IS_ERR(ethqos->serdes_phy)) {
+		ret = PTR_ERR(ethqos->serdes_phy);
+		goto out_config_dt;
+	}
+
 	ethqos->speed = SPEED_1000;
 	ethqos_update_rgmii_clk(ethqos, SPEED_1000);
 	ethqos_set_func_clk_en(ethqos);
@@ -665,6 +697,11 @@ static int qcom_ethqos_probe(struct platform_device *pdev)
 	if (of_device_is_compatible(np, "qcom,qcs404-ethqos"))
 		plat_dat->rx_clk_runs_in_lpi = 1;
 
+	if (ethqos->serdes_phy) {
+		plat_dat->serdes_powerup = qcom_ethqos_serdes_powerup;
+		plat_dat->serdes_powerdown  = qcom_ethqos_serdes_powerdown;
+	}
+
 	ret = stmmac_dvr_probe(dev, plat_dat, &stmmac_res);
 	if (ret)
 		goto out_config_dt;