net: phy: vitesse: implement downshift in vsc73xx phys

This commit implements downshift feature in vsc73xx family phys.

By default downshift was enabled with maximum tries.
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/vitesse.c

@@ -10,8 +10,10 @@
 #include <linux/mii.h>
 #include <linux/ethtool.h>
 #include <linux/phy.h>
+#include <linux/bitfield.h>
 
 /* Vitesse Extended Page Magic Register(s) */
+#define MII_VSC73XX_EXT_PAGE_1E		0x01
 #define MII_VSC82X4_EXT_PAGE_16E	0x10
 #define MII_VSC82X4_EXT_PAGE_17E	0x11
 #define MII_VSC82X4_EXT_PAGE_18E	0x12
@@ -60,6 +62,15 @@
 /* Vitesse Extended Page Access Register */
 #define MII_VSC82X4_EXT_PAGE_ACCESS	0x1f
 
+/* Vitesse VSC73XX Extended Control Register */
+#define MII_VSC73XX_PHY_CTRL_EXT3		0x14
+
+#define MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_EN	BIT(4)
+#define MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_CNT	GENMASK(3, 2)
+#define MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_STA	BIT(1)
+#define MII_VSC73XX_DOWNSHIFT_MAX		5
+#define MII_VSC73XX_DOWNSHIFT_INVAL		1
+
 /* Vitesse VSC8601 Extended PHY Control Register 1 */
 #define MII_VSC8601_EPHY_CTL		0x17
 #define MII_VSC8601_EPHY_CTL_RGMII_SKEW	(1 << 8)
@@ -128,6 +139,74 @@ static int vsc73xx_write_page(struct phy_device *phydev, int page)
 	return __phy_write(phydev, VSC73XX_EXT_PAGE_ACCESS, page);
 }
 
+static int vsc73xx_get_downshift(struct phy_device *phydev, u8 *data)
+{
+	int val, enable, cnt;
+
+	val = phy_read_paged(phydev, MII_VSC73XX_EXT_PAGE_1E,
+			     MII_VSC73XX_PHY_CTRL_EXT3);
+	if (val < 0)
+		return val;
+
+	enable = FIELD_GET(MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_EN, val);
+	cnt = FIELD_GET(MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_CNT, val) + 2;
+
+	*data = enable ? cnt : DOWNSHIFT_DEV_DISABLE;
+
+	return 0;
+}
+
+static int vsc73xx_set_downshift(struct phy_device *phydev, u8 cnt)
+{
+	u16 mask, val;
+	int ret;
+
+	if (cnt > MII_VSC73XX_DOWNSHIFT_MAX)
+		return -E2BIG;
+	else if (cnt == MII_VSC73XX_DOWNSHIFT_INVAL)
+		return -EINVAL;
+
+	mask = MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_EN;
+
+	if (!cnt) {
+		val = 0;
+	} else {
+		mask |= MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_CNT;
+		val = MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_EN |
+		      FIELD_PREP(MII_VSC73XX_PHY_CTRL_EXT3_DOWNSHIFT_CNT,
+				 cnt - 2);
+	}
+
+	ret = phy_modify_paged(phydev, MII_VSC73XX_EXT_PAGE_1E,
+			       MII_VSC73XX_PHY_CTRL_EXT3, mask, val);
+	if (ret < 0)
+		return ret;
+
+	return genphy_soft_reset(phydev);
+}
+
+static int vsc73xx_get_tunable(struct phy_device *phydev,
+			       struct ethtool_tunable *tuna, void *data)
+{
+	switch (tuna->id) {
+	case ETHTOOL_PHY_DOWNSHIFT:
+		return vsc73xx_get_downshift(phydev, data);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static int vsc73xx_set_tunable(struct phy_device *phydev,
+			       struct ethtool_tunable *tuna, const void *data)
+{
+	switch (tuna->id) {
+	case ETHTOOL_PHY_DOWNSHIFT:
+		return vsc73xx_set_downshift(phydev, *(const u8 *)data);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
 static void vsc73xx_config_init(struct phy_device *phydev)
 {
 	/* Receiver init */
@@ -137,6 +216,9 @@ static void vsc73xx_config_init(struct phy_device *phydev)
 
 	/* Config LEDs 0x61 */
 	phy_modify(phydev, MII_TPISTATUS, 0xff00, 0x0061);
+
+	/* Enable downshift by default */
+	vsc73xx_set_downshift(phydev, MII_VSC73XX_DOWNSHIFT_MAX);
 }
 
 static int vsc738x_config_init(struct phy_device *phydev)
@@ -447,6 +529,8 @@ static struct phy_driver vsc82xx_driver[] = {
 	.config_aneg    = vsc73xx_config_aneg,
 	.read_page      = vsc73xx_read_page,
 	.write_page     = vsc73xx_write_page,
+	.get_tunable    = vsc73xx_get_tunable,
+	.set_tunable    = vsc73xx_set_tunable,
 }, {
 	.phy_id         = PHY_ID_VSC7388,
 	.name           = "Vitesse VSC7388",
@@ -456,6 +540,8 @@ static struct phy_driver vsc82xx_driver[] = {
 	.config_aneg    = vsc73xx_config_aneg,
 	.read_page      = vsc73xx_read_page,
 	.write_page     = vsc73xx_write_page,
+	.get_tunable    = vsc73xx_get_tunable,
+	.set_tunable    = vsc73xx_set_tunable,
 }, {
 	.phy_id         = PHY_ID_VSC7395,
 	.name           = "Vitesse VSC7395",
@@ -465,6 +551,8 @@ static struct phy_driver vsc82xx_driver[] = {
 	.config_aneg    = vsc73xx_config_aneg,
 	.read_page      = vsc73xx_read_page,
 	.write_page     = vsc73xx_write_page,
+	.get_tunable    = vsc73xx_get_tunable,
+	.set_tunable    = vsc73xx_set_tunable,
 }, {
 	.phy_id         = PHY_ID_VSC7398,
 	.name           = "Vitesse VSC7398",
@@ -474,6 +562,8 @@ static struct phy_driver vsc82xx_driver[] = {
 	.config_aneg    = vsc73xx_config_aneg,
 	.read_page      = vsc73xx_read_page,
 	.write_page     = vsc73xx_write_page,
+	.get_tunable    = vsc73xx_get_tunable,
+	.set_tunable    = vsc73xx_set_tunable,
 }, {
 	.phy_id         = PHY_ID_VSC8662,
 	.name           = "Vitesse VSC8662",