net: dsa: mv88e6060: add phylink_get_caps implementation

Add a phylink_get_caps implementation for Marvell 88e6060 DSA switch.
This is a fast ethernet switch, with internal PHYs for ports 0 through
4. Port 4 also supports MII, REVMII, REVRMII and SNI. Port 5 supports
MII, REVMII, REVRMII and SNI without an internal PHY.

Reviewed-by: Andrew Lunn <[e-mail]>
Signed-off-by: Russell King (Oracle) <[e-mail]>
Reviewed-by: Vladimir Oltean <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/dsa/mv88e6060.c

···
 	return reg_write(priv, addr, regnum, val);
 }
 
+static void mv88e6060_phylink_get_caps(struct dsa_switch *ds, int port,
+				       struct phylink_config *config)
+{
+	unsigned long *interfaces = config->supported_interfaces;
+	struct mv88e6060_priv *priv = ds->priv;
+	int addr = REG_PORT(port);
+	int ret;
+
+	ret = reg_read(priv, addr, PORT_STATUS);
+	if (ret < 0) {
+		dev_err(ds->dev,
+			"port %d: unable to read status register: %pe\n",
+			port, ERR_PTR(ret));
+		return;
+	}
+
+	/* If the port is configured in SNI mode (acts as a 10Mbps PHY),
+	 * it should have phy-mode = "sni", but that doesn't yet exist, so
+	 * forcibly fail validation until the need arises to introduce it.
+	 */
+	if (!(ret & PORT_STATUS_PORTMODE)) {
+		dev_warn(ds->dev, "port %d: SNI mode not supported\n", port);
+		return;
+	}
+
+	config->mac_capabilities = MAC_100 | MAC_10 | MAC_SYM_PAUSE;
+
+	if (port >= 4) {
+		/* Ports 4 and 5 can support MII, REVMII and REVRMII modes */
+		__set_bit(PHY_INTERFACE_MODE_MII, interfaces);
+		__set_bit(PHY_INTERFACE_MODE_REVMII, interfaces);
+		__set_bit(PHY_INTERFACE_MODE_REVRMII, interfaces);
+	}
+	if (port <= 4) {
+		/* Ports 0 to 3 have internal PHYs, and port 4 can optionally
+		 * use an internal PHY.
+		 */
+		/* Internal PHY */
+		__set_bit(PHY_INTERFACE_MODE_INTERNAL, interfaces);
+		/* Default phylib interface mode */
+		__set_bit(PHY_INTERFACE_MODE_GMII, interfaces);
+	}
+}
+
 static const struct dsa_switch_ops mv88e6060_switch_ops = {
 	.get_tag_protocol = mv88e6060_get_tag_protocol,
 	.setup		= mv88e6060_setup,
 	.phy_read	= mv88e6060_phy_read,
 	.phy_write	= mv88e6060_phy_write,
+	.phylink_get_caps = mv88e6060_phylink_get_caps,
 };
 
 static int mv88e6060_probe(struct mdio_device *mdiodev)