net: phy: adin: Add flag to allow enabling of 1000base-t retrain

The PHY contains a retrain function which if enabled, retrains the
1000base-t link when the receiver status becomes not okay. If disabled,
the link will simply drop. This retrain function should be enabled in
order to be IEEE compliant, but is disabled by default on the PHY due to
FLD being enabled by default.

Add a device tree flag which can be used to enable the function on the
PHY when desired.

Signed-off-by: Ken Sloat <ken.s@variscite.com>

drivers/net/phy/adin.c

@@ -80,6 +80,8 @@
 #define   ADIN1300_FLD_SLCR_IN_INVLD_1000_EN	BIT(0)
 #define ADIN1300_CLOCK_STOP_REG			0x9400
 #define ADIN1300_LPI_WAKE_ERR_CNT_REG		0xa000
+#define ADIN1300_B_1000_RTRN_EN_REG		0xa001
+#define   ADIN1300_B_1000_RTRN_EN		BIT(0)
 
 #define ADIN1300_CDIAG_RUN			0xba1b
 #define   ADIN1300_CDIAG_RUN_EN			BIT(0)
@@ -505,6 +507,18 @@ static int adin_fast_down_disable(struct phy_device *phydev)
 		return 0;
 }
 
+static int adin_enable_retrain(struct phy_device *phydev)
+{
+	struct device *dev = &phydev->mdio.dev;
+
+	if (device_property_read_bool(dev, "adi,1000base-t-retrain-en"))
+		return phy_set_bits_mmd(phydev, MDIO_MMD_VEND1,
+			      ADIN1300_B_1000_RTRN_EN_REG,
+			      ADIN1300_B_1000_RTRN_EN);
+
+	return 0;
+}
+
 static int adin_config_init(struct phy_device *phydev)
 {
 	int rc;
@@ -531,6 +545,10 @@ static int adin_config_init(struct phy_device *phydev)
 	if (rc < 0)
 		return rc;
 
+	rc = adin_enable_retrain(phydev);
+	if (rc < 0)
+		return rc;
+
 	phydev_dbg(phydev, "PHY is using mode '%s'\n",
 		   phy_modes(phydev->interface));