net: phy: mscc: RGMII skew delay configuration

This patch adds support for configuring the RGMII skew delays in Rx and
Tx. The Rx and Tx skews are set based on the interface mode. By default
their configuration is set to the default value in hardware (0.2ns);
this means the driver do not rely anymore on the bootloader
configuration.

Then based on the interface mode being used, a 2ns delay is added:
- RGMII_ID adds it for both Rx and Tx.
- RGMII_RXID adds it for Rx.
- RGMII_TXID adds it for Tx.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/net/phy/mscc/mscc_main.c b/drivers/net/phy/mscc/mscc_main.c
index 86bb5c3c911a..5d78732de702 100644
--- a/drivers/net/phy/mscc/mscc_main.c
+++ b/drivers/net/phy/mscc/mscc_main.c
@@ -1288,6 +1288,32 @@ static bool vsc8584_is_pkg_init(struct phy_device *phydev, bool reversed)
 	return false;
 }
 
+static void vsc8584_rgmii_set_skews(struct phy_device *phydev)
+{
+	u32 skew_rx, skew_tx;
+
+	/* We first set the Rx and Tx skews to their default value in h/w
+	 * (0.2 ns).
+	 */
+	skew_rx = VSC8584_RGMII_SKEW_0_2;
+	skew_tx = VSC8584_RGMII_SKEW_0_2;
+
+	/* We then set the skews based on the interface mode. */
+	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
+	    phydev->interface == PHY_INTERFACE_MODE_RGMII_RXID)
+		skew_rx = VSC8584_RGMII_SKEW_2_0;
+	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
+	    phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID)
+		skew_tx = VSC8584_RGMII_SKEW_2_0;
+
+	/* Finally we apply the skews configuration. */
+	phy_modify_paged(phydev, MSCC_PHY_PAGE_EXTENDED_2,
+			 MSCC_PHY_RGMII_SETTINGS,
+			 (0x7 << RGMII_SKEW_RX_POS) | (0x7 << RGMII_SKEW_TX_POS),
+			 (skew_rx << RGMII_SKEW_RX_POS) |
+			 (skew_tx << RGMII_SKEW_TX_POS));
+}
+
 static int vsc8584_config_init(struct phy_device *phydev)
 {
 	struct vsc8531_private *vsc8531 = phydev->priv;
@@ -1422,6 +1448,9 @@ static int vsc8584_config_init(struct phy_device *phydev)
 	if (ret)
 		return ret;
 
+	if (phy_interface_is_rgmii(phydev))
+		vsc8584_rgmii_set_skews(phydev);
+
 	ret = genphy_soft_reset(phydev);
 	if (ret)
 		return ret;