net: phy: realtek: fix enabling of the TX-delay for RTL8211F

The old logic always enabled the TX-delay when the phy-mode was set to
PHY_INTERFACE_MODE_RGMII. There are dedicated phy-modes which tell the
PHY driver to enable the RX and/or TX delays:
- PHY_INTERFACE_MODE_RGMII should disable the RX and TX delay in the
  PHY (if required, the MAC should add the delays in this case)
- PHY_INTERFACE_MODE_RGMII_ID should enable RX and TX delay in the PHY
- PHY_INTERFACE_MODE_RGMII_TXID should enable the TX delay in the PHY
- PHY_INTERFACE_MODE_RGMII_RXID should enable the RX delay in the PHY
  (currently not supported by RTL8211F)

With this patch we enable the TX delay for PHY_INTERFACE_MODE_RGMII_ID
and PHY_INTERFACE_MODE_RGMII_TXID.
Additionally we now explicity disable the TX-delay, which seems to be
enabled automatically after a hard-reset of the PHY (by triggering it's
reset pin) to get a consistent state (as defined by the phy-mode).

This fixes a compatibility problem with some SoCs where the TX-delay was
also added by the MAC. With the TX-delay being applied twice the TX
clock was off and TX traffic was broken or very slow (<10Mbit/s) on
1000Mbit/s links.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/realtek.c

@@ -102,15 +102,19 @@ static int rtl8211f_config_init(struct phy_device *phydev)
 	if (ret < 0)
 		return ret;
 
-	if (phydev->interface == PHY_INTERFACE_MODE_RGMII) {
-		/* enable TXDLY */
 	phy_write(phydev, RTL8211F_PAGE_SELECT, 0xd08);
 	reg = phy_read(phydev, 0x11);
+
+	/* enable TX-delay for rgmii-id and rgmii-txid, otherwise disable it */
+	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
+	    phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID)
 		reg |= RTL8211F_TX_DELAY;
+	else
+		reg &= ~RTL8211F_TX_DELAY;
+
 	phy_write(phydev, 0x11, reg);
 	/* restore to default page 0 */
 	phy_write(phydev, RTL8211F_PAGE_SELECT, 0x0);
-	}
 
 	return 0;
 }