net: phylink: require supported_interfaces to be filled

We have been requiring the supported_interfaces bitmap to be filled in
by MAC drivers that have a mac_select_pcs() method. Now that all MAC
drivers fill in the supported_interfaces bitmap, it is time to enforce
this. We have already required supported_interfaces to be set in order
for optical SFPs to be configured in commit f81fa96d ("net: phylink:
use phy_interface_t bitmaps for optical modules").

Refuse phylink creation if supported_interfaces is empty, and remove
code to deal with cases where this mask is empty.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/E1q0K1u-006EIP-ET@rmk-PC.armlinux.org.ukSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/phylink.c

@@ -712,14 +712,11 @@ static int phylink_validate(struct phylink *pl, unsigned long *supported,
 {
 	const unsigned long *interfaces = pl->config->supported_interfaces;
 
-	if (!phy_interface_empty(interfaces)) {
-		if (state->interface == PHY_INTERFACE_MODE_NA)
-			return phylink_validate_mask(pl, supported, state,
-						     interfaces);
+	if (state->interface == PHY_INTERFACE_MODE_NA)
+		return phylink_validate_mask(pl, supported, state, interfaces);
 
-		if (!test_bit(state->interface, interfaces))
-			return -EINVAL;
-	}
+	if (!test_bit(state->interface, interfaces))
+		return -EINVAL;
 
 	return phylink_validate_mac_and_pcs(pl, supported, state);
 }
@@ -1513,19 +1510,18 @@ struct phylink *phylink_create(struct phylink_config *config,
 	struct phylink *pl;
 	int ret;
 
-	if (mac_ops->mac_select_pcs &&
-	    mac_ops->mac_select_pcs(config, PHY_INTERFACE_MODE_NA) !=
-	      ERR_PTR(-EOPNOTSUPP))
-		using_mac_select_pcs = true;
-
 	/* Validate the supplied configuration */
-	if (using_mac_select_pcs &&
-	    phy_interface_empty(config->supported_interfaces)) {
+	if (phy_interface_empty(config->supported_interfaces)) {
 		dev_err(config->dev,
-			"phylink: error: empty supported_interfaces but mac_select_pcs() method present\n");
+			"phylink: error: empty supported_interfaces\n");
 		return ERR_PTR(-EINVAL);
 	}
 
+	if (mac_ops->mac_select_pcs &&
+	    mac_ops->mac_select_pcs(config, PHY_INTERFACE_MODE_NA) !=
+	      ERR_PTR(-EOPNOTSUPP))
+		using_mac_select_pcs = true;
+
 	pl = kzalloc(sizeof(*pl), GFP_KERNEL);
 	if (!pl)
 		return ERR_PTR(-ENOMEM);