[PATCH net 6/6] net: phy: vitesse: repair vsc73xx autonegotiation

[Pawel Dembicki <paweldembicki@gmail.com>]

When the vsc73xx mdio bus work properly, the generic autonegotiation
configuration works well.

Vsc73xx have auto MDI-X disabled by default in forced mode. This commit
enables it.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
---
This patch came from net-next series[0].
Changes since net-next:
  - rebased to netdev/main only

[0] https://patchwork.kernel.org/project/netdevbpf/patch/20240729210615.279952-6-paweldembicki@gmail.com/
---
 drivers/net/phy/vitesse.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/net/phy/vitesse.c b/drivers/net/phy/vitesse.c
index 897b979ec03c..19b7bf189be5 100644
--- a/drivers/net/phy/vitesse.c
+++ b/drivers/net/phy/vitesse.c
@@ -60,6 +60,11 @@
 /* Vitesse Extended Page Access Register */
 #define MII_VSC82X4_EXT_PAGE_ACCESS	0x1f
 
+/* VSC73XX PHY_BYPASS_CTRL register*/
+#define MII_VSC73XX_PHY_BYPASS_CTRL		MII_DCOUNTER
+#define MII_PBC_FORCED_SPEED_AUTO_MDIX_DIS	BIT(7)
+#define MII_VSC73XX_PBC_AUTO_NP_EXCHANGE_DIS	BIT(1)
+
 /* Vitesse VSC8601 Extended PHY Control Register 1 */
 #define MII_VSC8601_EPHY_CTL		0x17
 #define MII_VSC8601_EPHY_CTL_RGMII_SKEW	(1 << 8)
@@ -239,12 +244,20 @@ static int vsc739x_config_init(struct phy_device *phydev)
 
 static int vsc73xx_config_aneg(struct phy_device *phydev)
 {
-	/* The VSC73xx switches does not like to be instructed to
-	 * do autonegotiation in any way, it prefers that you just go
-	 * with the power-on/reset defaults. Writing some registers will
-	 * just make autonegotiation permanently fail.
-	 */
-	return 0;
+	int ret;
+
+	/* Enable Auto MDI-X in forced 10/100 mode */
+	if (phydev->autoneg != AUTONEG_ENABLE && phydev->speed <= SPEED_100) {
+		ret = genphy_setup_forced(phydev);
+
+		if (ret < 0) /* error */
+			return ret;
+
+		return phy_clear_bits(phydev, MII_VSC73XX_PHY_BYPASS_CTRL,
+				      MII_PBC_FORCED_SPEED_AUTO_MDIX_DIS);
+	}
+
+	return genphy_config_aneg(phydev);
 }
 
 /* This adds a skew for both TX and RX clocks, so the skew should only be
-- 
2.34.1