[PATCH 2/2] net: dsa: microchip: Provide Module 4 KSZ9477 errata (DS80000754C)

[Lukasz Majewski <lukma@denx.de>]

The KSZ9477 errata points out the link up/down problem when EEE is enabled
in the device to which the KSZ9477 tries to auto negotiate.

The suggested workaround is to clear advertisement EEE registers
(accessed as per port MMD one).

Signed-off-by: Lukasz Majewski <lukma@denx.de>
---
 drivers/net/dsa/microchip/ksz9477.c | 40 ++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index cb6aa7c668a8..563f497ba656 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -1128,6 +1128,44 @@ int ksz9477_enable_stp_addr(struct ksz_device *dev)
 	return 0;
 }
 
+static int ksz9477_errata(struct dsa_switch *ds)
+{
+	struct ksz_device *dev = ds->priv;
+	u16 val;
+	int p;
+
+	/* 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.
+	 *
+	 *   Only PHY ports (dsa user) [0-4] need to have the EEE advertisement
+	 *   bits cleared.
+	 */
+
+	for (p = 0; p < ds->num_ports; p++) {
+		if (!dsa_is_user_port(ds, p))
+			continue;
+
+		ksz9477_port_mmd_read(dev, p, MMD_DEVICE_ID_EEE_ADV,
+				      MMD_EEE_ADV, &val, 1);
+
+		pr_err("%s: PORT: %d val: 0x%x pc: %d\n", __func__, p, val,
+		       ds->num_ports);
+
+		val &= ~(EEE_ADV_100MBIT | EEE_ADV_1GBIT);
+		ksz9477_port_mmd_write(dev, p, MMD_DEVICE_ID_EEE_ADV,
+				       MMD_EEE_ADV, &val, 1);
+	}
+
+	return 0;
+}
+
 int ksz9477_setup(struct dsa_switch *ds)
 {
 	struct ksz_device *dev = ds->priv;
@@ -1157,7 +1195,7 @@ int ksz9477_setup(struct dsa_switch *ds)
 	/* enable global MIB counter freeze function */
 	ksz_cfg(dev, REG_SW_MAC_CTRL_6, SW_MIB_COUNTER_FREEZE, true);
 
-	return 0;
+	return ksz9477_errata(ds);
 }
 
 u32 ksz9477_get_port_addr(int port, int offset)
-- 
2.20.1