[PATCH net-next v2] net: phylink: add phylink_pcs_loopback() method for PCS loopback support

@@ -168,6 +168,22 @@ static void dwmac_integrated_pcs_an_restart(struct phylink_pcs *pcs)
 	}
 }
 
+static int dwmac_integrated_pcs_loopback(struct phylink_pcs *pcs, bool enable)
+{
+	struct stmmac_pcs *spcs = phylink_pcs_to_stmmac_pcs(pcs);
+	void __iomem *an_control = spcs->base + GMAC_AN_CTRL(0);
+	u32 ctrl;
+
+	ctrl = readl(an_control);
+	if (enable)
+		ctrl |= GMAC_AN_CTRL_ELE;
+	else
+		ctrl &= ~GMAC_AN_CTRL_ELE;
+	writel(ctrl, an_control);
+
+	return 0;
+}
+
 static const struct phylink_pcs_ops dwmac_integrated_pcs_ops = {
 	.pcs_inband_caps = dwmac_integrated_pcs_inband_caps,
 	.pcs_enable = dwmac_integrated_pcs_enable,

@@ -175,6 +191,7 @@ static const struct phylink_pcs_ops dwmac_integrated_pcs_ops = {
 	.pcs_get_state = dwmac_integrated_pcs_get_state,
 	.pcs_config = dwmac_integrated_pcs_config,
 	.pcs_an_restart = dwmac_integrated_pcs_an_restart,
+	.pcs_loopback = dwmac_integrated_pcs_loopback,
 };
 
 void stmmac_integrated_pcs_irq(struct stmmac_priv *priv, u32 status,

@@ -19,6 +19,7 @@
 #include <net/udp.h>
 #include <net/tc_act/tc_gact.h>
 #include "stmmac.h"
+#include "stmmac_pcs.h"
 
 struct stmmachdr {
 	__be32 version;

@@ -374,23 +375,51 @@ static int stmmac_test_mac_loopback(struct stmmac_priv *priv)
 	return __stmmac_test_loopback(priv, &attr);
 }
 
+static struct phylink_pcs *stmmac_selftest_get_pcs(struct stmmac_priv *priv)
+{
+	/* Try glue driver's PCS first, then the integrated PCS. */
+	if (priv->hw->phylink_pcs)
+		return priv->hw->phylink_pcs;
+
+	if (priv->integrated_pcs)
+		return &priv->integrated_pcs->pcs;
+
+	return NULL;
+}
+
 static int stmmac_test_phy_loopback(struct stmmac_priv *priv)
 {
 	struct stmmac_packet_attrs attr = { };
+	struct phylink_pcs *pcs;
 	int ret;
 
-	if (!priv->dev->phydev)
-		return -EOPNOTSUPP;
+	if (priv->dev->phydev) {
+		ret = phy_loopback(priv->dev->phydev, true, 0);
+		if (ret)
+			return ret;
 
-	ret = phy_loopback(priv->dev->phydev, true, 0);
-	if (ret)
+		attr.dst = priv->dev->dev_addr;
+		ret = __stmmac_test_loopback(priv, &attr);
+
+		phy_loopback(priv->dev->phydev, false, 0);
 		return ret;
+	}
 
-	attr.dst = priv->dev->dev_addr;
-	ret = __stmmac_test_loopback(priv, &attr);
+	/* Use PCS loopback for interfaces without an external PHY. */
+	pcs = stmmac_selftest_get_pcs(priv);
+	if (pcs) {
+		ret = phylink_pcs_loopback(pcs, true);
+		if (ret)
+			return ret;
 
-	phy_loopback(priv->dev->phydev, false, 0);
-	return ret;
+		attr.dst = priv->dev->dev_addr;
+		ret = __stmmac_test_loopback(priv, &attr);
+
+		phylink_pcs_loopback(pcs, false);
+		return ret;
+	}
+
+	return -EOPNOTSUPP;
 }
 
 static int stmmac_test_mmc(struct stmmac_priv *priv)

@@ -1986,6 +2015,9 @@ void stmmac_selftest_run(struct net_device *dev,
 			ret = -EOPNOTSUPP;
 			if (dev->phydev)
 				ret = phy_loopback(dev->phydev, true, 0);
+			else
+				ret = phylink_pcs_loopback(stmmac_selftest_get_pcs(priv),
+							   true);
 			if (!ret)
 				break;
 			fallthrough;

@@ -2019,6 +2051,9 @@ void stmmac_selftest_run(struct net_device *dev,
 			ret = -EOPNOTSUPP;
 			if (dev->phydev)
 				ret = phy_loopback(dev->phydev, false, 0);
+			else
+				ret = phylink_pcs_loopback(stmmac_selftest_get_pcs(priv),
+							   false);
 			if (!ret)
 				break;
 			fallthrough;

@@ -997,6 +997,25 @@ int phylink_pcs_pre_init(struct phylink *pl, struct phylink_pcs *pcs)
 }
 EXPORT_SYMBOL_GPL(phylink_pcs_pre_init);
 
+/**
+ * phylink_pcs_loopback() - Enable or disable loopback at the PCS
+ * @pcs: a pointer to a &struct phylink_pcs.
+ * @enable: true to enable loopback, false to disable
+ *
+ * Enable or disable loopback mode at the PCS level. This is used by MAC
+ * drivers for selftest purposes when no external PHY is present.
+ *
+ * Returns 0 on success, negative error code on failure.
+ */
+int phylink_pcs_loopback(struct phylink_pcs *pcs, bool enable)
+{
+	if (pcs && pcs->ops->pcs_loopback)
+		return pcs->ops->pcs_loopback(pcs, enable);
+
+	return -EOPNOTSUPP;
+}
+EXPORT_SYMBOL_GPL(phylink_pcs_loopback);
+
 static void phylink_mac_config(struct phylink *pl,
 			       const struct phylink_link_state *state)
 {

@@ -518,6 +518,7 @@ struct phylink_pcs {
  *		    the MAC.
  * @pcs_pre_init: configure PCS components necessary for MAC hardware
  *                initialization e.g. RX clock for stmmac.
+ * @pcs_loopback: enable/disable loopback mode at the PCS.
  */
 struct phylink_pcs_ops {
 	int (*pcs_validate)(struct phylink_pcs *pcs, unsigned long *supported,

@@ -542,6 +543,7 @@ struct phylink_pcs_ops {
 	void (*pcs_disable_eee)(struct phylink_pcs *pcs);
 	void (*pcs_enable_eee)(struct phylink_pcs *pcs);
 	int (*pcs_pre_init)(struct phylink_pcs *pcs);
+	int (*pcs_loopback)(struct phylink_pcs *pcs, bool enable);
 };
 
 #if 0 /* For kernel-doc purposes only. */

@@ -717,8 +719,22 @@ void pcs_enable_eee(struct phylink_pcs *pcs);
  */
 int pcs_pre_init(struct phylink_pcs *pcs);
 
+/**
+ * pcs_loopback() - Enable or disable loopback at the PCS
+ * @pcs: a pointer to a &struct phylink_pcs.
+ * @enable: true to enable loopback, false to disable
+ *
+ * Enable or disable loopback mode at the PCS level. This is used by MAC
+ * drivers for selftest purposes when no external PHY is present.
+ *
+ * Returns 0 on success, or a negative error code on failure.
+ */
+int pcs_loopback(struct phylink_pcs *pcs, bool enable);
+
 #endif
 
+int phylink_pcs_loopback(struct phylink_pcs *pcs, bool enable);
+
 struct phylink *phylink_create(struct phylink_config *,
 			       const struct fwnode_handle *,
 			       phy_interface_t,