phylink: Improve error message when validate failed

This should improve the error message when the PHY validate in the MAC
driver failed. I ran into this problem multiple times that I put wrong
interface values into the device tree and was searching why it is
failing with -22 (-EINVAL). This should make it easier to spot the
problem.
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phylink.c

@@ -761,8 +761,14 @@ static int phylink_bringup_phy(struct phylink *pl, struct phy_device *phy,
 		config.interface = interface;
 
 	ret = phylink_validate(pl, supported, &config);
-	if (ret)
+	if (ret) {
+		phylink_warn(pl, "validation of %s with support %*pb and advertisement %*pb failed: %d\n",
+			     phy_modes(config.interface),
+			     __ETHTOOL_LINK_MODE_MASK_NBITS, phy->supported,
+			     __ETHTOOL_LINK_MODE_MASK_NBITS, config.advertising,
+			     ret);
 		return ret;
+	}
 
 	phy->phylink = pl;
 	phy->phy_link_change = phylink_phy_change;