The KSZ9477 errata points out (in 'Module 4') the link up/down problem
when EEE (Energy Efficient Ethernet) is enabled in the device to which
the KSZ9477 tries to auto negotiate.

The suggested workaround is to clear advertisement of EEE for PHYs in
this chip driver.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
---
 drivers/net/phy/micrel.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
index 87b090ad2874..469dcd8a5711 100644
--- a/drivers/net/phy/micrel.c
+++ b/drivers/net/phy/micrel.c

@@ -1418,6 +1418,35 @@ static int ksz9131_get_features(struct phy_device *phydev)
 	return 0;
 }
 
+static int ksz9477_get_features(struct phy_device *phydev)
+{
+	__ETHTOOL_DECLARE_LINK_MODE_MASK(zero) = { 0, };
+	int ret;
+
+	ret = genphy_read_abilities(phydev);
+	if (ret)
+		return ret;
+
+	/* KSZ9477 Errata DS80000754C
+	 *
+	 * Module 4: Energy Efficient Ethernet (EEE) feature select must be
+	 * manually disabled
+	 *   The EEE feature is enabled by default, but it is not fully
+	 *   operational. It must be manually disabled through register
+	 *   controls. If not disabled, the PHY ports can auto-negotiate
+	 *   to enable EEE, and this feature can cause link drops when linked
+	 *   to another device supporting EEE.
+	 *
+	 *   Although, the KSZ9477 MMD register
+	 *   (MMD_DEVICE_ID_EEE_ADV.MMD_EEE_ADV) advertise that EEE is
+	 *   operational one needs to manualy clear them to follow the chip
+	 *   errata.
+	 */
+	linkmode_and(phydev->supported_eee, phydev->supported, zero);
+
+	return 0;
+}
+
 #define KSZ8873MLL_GLOBAL_CONTROL_4	0x06
 #define KSZ8873MLL_GLOBAL_CONTROL_4_DUPLEX	BIT(6)
 #define KSZ8873MLL_GLOBAL_CONTROL_4_SPEED	BIT(4)

@@ -4871,7 +4900,7 @@ static struct phy_driver ksphy_driver[] = {
 	.handle_interrupt = kszphy_handle_interrupt,
 	.suspend	= genphy_suspend,
 	.resume		= genphy_resume,
-	.get_features	= ksz9131_get_features,
+	.get_features	= ksz9477_get_features,