net: dsa: qca8k: add tracking state of master port

MDIO/MIB Ethernet require the master port and the tagger availabale to
correctly work. Use the new api master_state_change to track when master
is operational or not and set a bool in qca8k_priv.
We cache the first cached master available and we check if other cpu
port are operational when the cached one goes down.
This cached master will later be used by mdio read/write and mib request to
correctly use the working function.

qca8k implementation for MDIO/MIB Ethernet is bad. CPU port0 is the only
one that answers with the ack packet or sends MIB Ethernet packets. For
this reason the master_state_change ignore CPU port6 and only checks
CPU port0 if it's operational and enables this mode.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/qca8k.c

@@ -2383,6 +2383,20 @@ qca8k_port_lag_leave(struct dsa_switch *ds, int port,
 	return qca8k_lag_refresh_portmap(ds, port, lag, true);
 }
 
+static void
+qca8k_master_change(struct dsa_switch *ds, const struct net_device *master,
+		    bool operational)
+{
+	struct dsa_port *dp = master->dsa_ptr;
+	struct qca8k_priv *priv = ds->priv;
+
+	/* Ethernet MIB/MDIO is only supported for CPU port 0 */
+	if (dp->index != 0)
+		return;
+
+	priv->mgmt_master = operational ? (struct net_device *)master : NULL;
+}
+
 static const struct dsa_switch_ops qca8k_switch_ops = {
 	.get_tag_protocol	= qca8k_get_tag_protocol,
 	.setup			= qca8k_setup,
@@ -2418,6 +2432,7 @@ static const struct dsa_switch_ops qca8k_switch_ops = {
 	.get_phy_flags		= qca8k_get_phy_flags,
 	.port_lag_join		= qca8k_port_lag_join,
 	.port_lag_leave		= qca8k_port_lag_leave,
+	.master_state_change	= qca8k_master_change,
 };
 
 static int qca8k_read_switch_id(struct qca8k_priv *priv)

drivers/net/dsa/qca8k.h

@@ -353,6 +353,7 @@ struct qca8k_priv {
 	struct dsa_switch_ops ops;
 	struct gpio_desc *reset_gpio;
 	unsigned int port_mtu[QCA8K_NUM_PORTS];
+	struct net_device *mgmt_master; /* Track if mdio/mib Ethernet is available */
 };
 
 struct qca8k_mib_desc {