net: phy: at803x: add downshift support

The AR8031 and AR8035 support the link speed downshift. Add driver
support for it. One peculiarity of these PHYs is that it needs a
software reset after changing the setting, thus add the .soft_reset()
op and do a phy_init_hw() if necessary.

This was tested on a custom board with the AR8031.
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/at803x.c

@@ -43,6 +43,9 @@
 #define AT803X_INTR_STATUS			0x13
 
 #define AT803X_SMART_SPEED			0x14
+#define AT803X_SMART_SPEED_ENABLE		BIT(5)
+#define AT803X_SMART_SPEED_RETRY_LIMIT_MASK	GENMASK(4, 2)
+#define AT803X_SMART_SPEED_BYPASS_TIMER		BIT(1)
 #define AT803X_LED_CONTROL			0x18
 
 #define AT803X_DEVICE_ADDR			0x03
@@ -103,6 +106,10 @@
 #define AT803X_CLK_OUT_STRENGTH_HALF		1
 #define AT803X_CLK_OUT_STRENGTH_QUARTER		2
 
+#define AT803X_DEFAULT_DOWNSHIFT 5
+#define AT803X_MIN_DOWNSHIFT 2
+#define AT803X_MAX_DOWNSHIFT 9
+
 #define ATH9331_PHY_ID 0x004dd041
 #define ATH8030_PHY_ID 0x004dd076
 #define ATH8031_PHY_ID 0x004dd074
@@ -713,6 +720,80 @@ static int at803x_read_status(struct phy_device *phydev)
 	return 0;
 }
 
+static int at803x_get_downshift(struct phy_device *phydev, u8 *d)
+{
+	int val;
+
+	val = phy_read(phydev, AT803X_SMART_SPEED);
+	if (val < 0)
+		return val;
+
+	if (val & AT803X_SMART_SPEED_ENABLE)
+		*d = FIELD_GET(AT803X_SMART_SPEED_RETRY_LIMIT_MASK, val) + 2;
+	else
+		*d = DOWNSHIFT_DEV_DISABLE;
+
+	return 0;
+}
+
+static int at803x_set_downshift(struct phy_device *phydev, u8 cnt)
+{
+	u16 mask, set;
+	int ret;
+
+	switch (cnt) {
+	case DOWNSHIFT_DEV_DEFAULT_COUNT:
+		cnt = AT803X_DEFAULT_DOWNSHIFT;
+		fallthrough;
+	case AT803X_MIN_DOWNSHIFT ... AT803X_MAX_DOWNSHIFT:
+		set = AT803X_SMART_SPEED_ENABLE |
+		      AT803X_SMART_SPEED_BYPASS_TIMER |
+		      FIELD_PREP(AT803X_SMART_SPEED_RETRY_LIMIT_MASK, cnt - 2);
+		mask = AT803X_SMART_SPEED_RETRY_LIMIT_MASK;
+		break;
+	case DOWNSHIFT_DEV_DISABLE:
+		set = 0;
+		mask = AT803X_SMART_SPEED_ENABLE |
+		       AT803X_SMART_SPEED_BYPASS_TIMER;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	ret = phy_modify_changed(phydev, AT803X_SMART_SPEED, mask, set);
+
+	/* After changing the smart speed settings, we need to perform a
+	 * software reset, use phy_init_hw() to make sure we set the
+	 * reapply any values which might got lost during software reset.
+	 */
+	if (ret == 1)
+		ret = phy_init_hw(phydev);
+
+	return ret;
+}
+
+static int at803x_get_tunable(struct phy_device *phydev,
+			      struct ethtool_tunable *tuna, void *data)
+{
+	switch (tuna->id) {
+	case ETHTOOL_PHY_DOWNSHIFT:
+		return at803x_get_downshift(phydev, data);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static int at803x_set_tunable(struct phy_device *phydev,
+			      struct ethtool_tunable *tuna, const void *data)
+{
+	switch (tuna->id) {
+	case ETHTOOL_PHY_DOWNSHIFT:
+		return at803x_set_downshift(phydev, *(const u8 *)data);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
 static struct phy_driver at803x_driver[] = {
 {
 	/* Qualcomm Atheros AR8035 */
@@ -722,6 +803,7 @@ static struct phy_driver at803x_driver[] = {
 	.probe			= at803x_probe,
 	.remove			= at803x_remove,
 	.config_init		= at803x_config_init,
+	.soft_reset		= genphy_soft_reset,
 	.set_wol		= at803x_set_wol,
 	.get_wol		= at803x_get_wol,
 	.suspend		= at803x_suspend,
@@ -730,6 +812,8 @@ static struct phy_driver at803x_driver[] = {
 	.read_status		= at803x_read_status,
 	.ack_interrupt		= at803x_ack_interrupt,
 	.config_intr		= at803x_config_intr,
+	.get_tunable		= at803x_get_tunable,
+	.set_tunable		= at803x_set_tunable,
 }, {
 	/* Qualcomm Atheros AR8030 */
 	.phy_id			= ATH8030_PHY_ID,
@@ -754,6 +838,7 @@ static struct phy_driver at803x_driver[] = {
 	.probe			= at803x_probe,
 	.remove			= at803x_remove,
 	.config_init		= at803x_config_init,
+	.soft_reset		= genphy_soft_reset,
 	.set_wol		= at803x_set_wol,
 	.get_wol		= at803x_get_wol,
 	.suspend		= at803x_suspend,
@@ -763,6 +848,8 @@ static struct phy_driver at803x_driver[] = {
 	.aneg_done		= at803x_aneg_done,
 	.ack_interrupt		= &at803x_ack_interrupt,
 	.config_intr		= &at803x_config_intr,
+	.get_tunable		= at803x_get_tunable,
+	.set_tunable		= at803x_set_tunable,
 }, {
 	/* Qualcomm Atheros AR8032 */
 	PHY_ID_MATCH_EXACT(ATH8032_PHY_ID),