r8169: fix issue caused by buggy BIOS on certain boards with RTL8168d

On some boards with this chip version the BIOS is buggy and misses
to reset the PHY page selector. This results in the PHY ID read
accessing registers on a different page, returning a more or
less random value. Fix this by resetting the page selector first.

Fixes: f1e911d ("r8169: add basic phylib support")
Cc: stable@vger.kernel.org
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/64f2055e-98b8-45ec-8568-665e3d54d4e6@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/realtek/r8169_main.c

@@ -5164,6 +5164,15 @@ static int r8169_mdio_register(struct rtl8169_private *tp)
 	struct mii_bus *new_bus;
 	int ret;
 
+	/* On some boards with this chip version the BIOS is buggy and misses
+	 * to reset the PHY page selector. This results in the PHY ID read
+	 * accessing registers on a different page, returning a more or
+	 * less random value. Fix this by resetting the page selector first.
+	 */
+	if (tp->mac_version == RTL_GIGA_MAC_VER_25 ||
+	    tp->mac_version == RTL_GIGA_MAC_VER_26)
+		r8169_mdio_write(tp, 0x1f, 0);
+
 	new_bus = devm_mdiobus_alloc(&pdev->dev);
 	if (!new_bus)
 		return -ENOMEM;