net: phy: micrel: add phy-mode support for the KSZ9031 PHY

Add support for following phy-modes: rgmii, rgmii-id, rgmii-txid, rgmii-rxid.

This PHY has an internal RX delay of 1.2ns and no delay for TX.

The pad skew registers allow to set the total TX delay to max 1.38ns and
the total RX delay to max of 2.58ns (configurable 1.38ns + build in
1.2ns) and a minimal delay of 0ns.

According to the RGMII v1.3 specification the delay provided by PCB traces
should be between 1.5ns and 2.0ns. The RGMII v2.0 allows to provide this
delay by MAC or PHY. So, we configure this PHY to the best values we can
get by this HW: TX delay to 1.38ns (max supported value) and RX delay to
1.80ns (best calculated delay)

The phy-modes can still be fine tuned/overwritten by *-skew-ps
device tree properties described in:
Documentation/devicetree/bindings/net/micrel-ksz90x1.txt
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Philippe Schenker <philippe.schenker@toradex.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/micrel.c

@@ -19,6 +19,7 @@
  *			 ksz9477
  */
 
+#include <linux/bitfield.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/phy.h>
@@ -490,9 +491,50 @@ static int ksz9021_config_init(struct phy_device *phydev)
 
 /* MMD Address 0x2 */
 #define MII_KSZ9031RN_CONTROL_PAD_SKEW	4
+#define MII_KSZ9031RN_RX_CTL_M		GENMASK(7, 4)
+#define MII_KSZ9031RN_TX_CTL_M		GENMASK(3, 0)
+
 #define MII_KSZ9031RN_RX_DATA_PAD_SKEW	5
+#define MII_KSZ9031RN_RXD3		GENMASK(15, 12)
+#define MII_KSZ9031RN_RXD2		GENMASK(11, 8)
+#define MII_KSZ9031RN_RXD1		GENMASK(7, 4)
+#define MII_KSZ9031RN_RXD0		GENMASK(3, 0)
+
 #define MII_KSZ9031RN_TX_DATA_PAD_SKEW	6
+#define MII_KSZ9031RN_TXD3		GENMASK(15, 12)
+#define MII_KSZ9031RN_TXD2		GENMASK(11, 8)
+#define MII_KSZ9031RN_TXD1		GENMASK(7, 4)
+#define MII_KSZ9031RN_TXD0		GENMASK(3, 0)
+
 #define MII_KSZ9031RN_CLK_PAD_SKEW	8
+#define MII_KSZ9031RN_GTX_CLK		GENMASK(9, 5)
+#define MII_KSZ9031RN_RX_CLK		GENMASK(4, 0)
+
+/* KSZ9031 has internal RGMII_IDRX = 1.2ns and RGMII_IDTX = 0ns. To
+ * provide different RGMII options we need to configure delay offset
+ * for each pad relative to build in delay.
+ */
+/* keep rx as "No delay adjustment" and set rx_clk to +0.60ns to get delays of
+ * 1.80ns
+ */
+#define RX_ID				0x7
+#define RX_CLK_ID			0x19
+
+/* set rx to +0.30ns and rx_clk to -0.90ns to compensate the
+ * internal 1.2ns delay.
+ */
+#define RX_ND				0xc
+#define RX_CLK_ND			0x0
+
+/* set tx to -0.42ns and tx_clk to +0.96ns to get 1.38ns delay */
+#define TX_ID				0x0
+#define TX_CLK_ID			0x1f
+
+/* set tx and tx_clk to "No delay adjustment" to keep 0ns
+ * dealy
+ */
+#define TX_ND				0x7
+#define TX_CLK_ND			0xf
 
 /* MMD Address 0x1C */
 #define MII_KSZ9031RN_EDPD		0x23
@@ -501,7 +543,8 @@ static int ksz9021_config_init(struct phy_device *phydev)
 static int ksz9031_of_load_skew_values(struct phy_device *phydev,
 				       const struct device_node *of_node,
 				       u16 reg, size_t field_sz,
-				       const char *field[], u8 numfields)
+				       const char *field[], u8 numfields,
+				       bool *update)
 {
 	int val[4] = {-1, -2, -3, -4};
 	int matches = 0;
@@ -517,6 +560,8 @@ static int ksz9031_of_load_skew_values(struct phy_device *phydev,
 	if (!matches)
 		return 0;
 
+	*update |= true;
+
 	if (matches < numfields)
 		newval = phy_read_mmd(phydev, 2, reg);
 	else
@@ -565,6 +610,67 @@ static int ksz9031_enable_edpd(struct phy_device *phydev)
 			     reg | MII_KSZ9031RN_EDPD_ENABLE);
 }
 
+static int ksz9031_config_rgmii_delay(struct phy_device *phydev)
+{
+	u16 rx, tx, rx_clk, tx_clk;
+	int ret;
+
+	switch (phydev->interface) {
+	case PHY_INTERFACE_MODE_RGMII:
+		tx = TX_ND;
+		tx_clk = TX_CLK_ND;
+		rx = RX_ND;
+		rx_clk = RX_CLK_ND;
+		break;
+	case PHY_INTERFACE_MODE_RGMII_ID:
+		tx = TX_ID;
+		tx_clk = TX_CLK_ID;
+		rx = RX_ID;
+		rx_clk = RX_CLK_ID;
+		break;
+	case PHY_INTERFACE_MODE_RGMII_RXID:
+		tx = TX_ND;
+		tx_clk = TX_CLK_ND;
+		rx = RX_ID;
+		rx_clk = RX_CLK_ID;
+		break;
+	case PHY_INTERFACE_MODE_RGMII_TXID:
+		tx = TX_ID;
+		tx_clk = TX_CLK_ID;
+		rx = RX_ND;
+		rx_clk = RX_CLK_ND;
+		break;
+	default:
+		return 0;
+	}
+
+	ret = phy_write_mmd(phydev, 2, MII_KSZ9031RN_CONTROL_PAD_SKEW,
+			    FIELD_PREP(MII_KSZ9031RN_RX_CTL_M, rx) |
+			    FIELD_PREP(MII_KSZ9031RN_TX_CTL_M, tx));
+	if (ret < 0)
+		return ret;
+
+	ret = phy_write_mmd(phydev, 2, MII_KSZ9031RN_RX_DATA_PAD_SKEW,
+			    FIELD_PREP(MII_KSZ9031RN_RXD3, rx) |
+			    FIELD_PREP(MII_KSZ9031RN_RXD2, rx) |
+			    FIELD_PREP(MII_KSZ9031RN_RXD1, rx) |
+			    FIELD_PREP(MII_KSZ9031RN_RXD0, rx));
+	if (ret < 0)
+		return ret;
+
+	ret = phy_write_mmd(phydev, 2, MII_KSZ9031RN_TX_DATA_PAD_SKEW,
+			    FIELD_PREP(MII_KSZ9031RN_TXD3, tx) |
+			    FIELD_PREP(MII_KSZ9031RN_TXD2, tx) |
+			    FIELD_PREP(MII_KSZ9031RN_TXD1, tx) |
+			    FIELD_PREP(MII_KSZ9031RN_TXD0, tx));
+	if (ret < 0)
+		return ret;
+
+	return phy_write_mmd(phydev, 2, MII_KSZ9031RN_CLK_PAD_SKEW,
+			     FIELD_PREP(MII_KSZ9031RN_GTX_CLK, tx_clk) |
+			     FIELD_PREP(MII_KSZ9031RN_RX_CLK, rx_clk));
+}
+
 static int ksz9031_config_init(struct phy_device *phydev)
 {
 	const struct device *dev = &phydev->mdio.dev;
@@ -597,21 +703,33 @@ static int ksz9031_config_init(struct phy_device *phydev)
 	} while (!of_node && dev_walker);
 
 	if (of_node) {
+		bool update = false;
+
+		if (phy_interface_is_rgmii(phydev)) {
+			result = ksz9031_config_rgmii_delay(phydev);
+			if (result < 0)
+				return result;
+		}
+
 		ksz9031_of_load_skew_values(phydev, of_node,
 				MII_KSZ9031RN_CLK_PAD_SKEW, 5,
-				clk_skews, 2);
+				clk_skews, 2, &update);
 
 		ksz9031_of_load_skew_values(phydev, of_node,
 				MII_KSZ9031RN_CONTROL_PAD_SKEW, 4,
-				control_skews, 2);
+				control_skews, 2, &update);
 
 		ksz9031_of_load_skew_values(phydev, of_node,
 				MII_KSZ9031RN_RX_DATA_PAD_SKEW, 4,
-				rx_data_skews, 4);
+				rx_data_skews, 4, &update);
 
 		ksz9031_of_load_skew_values(phydev, of_node,
 				MII_KSZ9031RN_TX_DATA_PAD_SKEW, 4,
-				tx_data_skews, 4);
+				tx_data_skews, 4, &update);
+
+		if (update && phydev->interface != PHY_INTERFACE_MODE_RGMII)
+			phydev_warn(phydev,
+				    "*-skew-ps values should be used only with phy-mode = \"rgmii\"\n");
 
 		/* Silicon Errata Sheet (DS80000691D or DS80000692D):
 		 * When the device links in the 1000BASE-T slave mode only,