net: devlink: Add unused port flavour

Not all ports of a switch need to be used, particularly in embedded
systems. Add a port flavour for ports which physically exist in the
switch, but are not connected to the front panel etc, and so are
unused. By having unused ports present in devlink, it gives a more
accurate representation of the hardware. It also allows regions to be
associated to such ports, so allowing, for example, to determine
unused ports are correctly powered off, or to compare probable reset
defaults of unused ports to used ports experiences issues.

Actually registering unused ports and setting the flavour to unused is
optional. The DSA core will register all such switch ports, but such
ports are expected to be limited in number. Bigger ASICs may decide
not to list unused ports.

v2:
Expand the description about why it is useful
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Tested-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/devlink.h

@@ -197,6 +197,9 @@ enum devlink_port_flavour {
 				      * port that faces the PCI VF.
 				      */
 	DEVLINK_PORT_FLAVOUR_VIRTUAL, /* Any virtual port facing the user. */
+	DEVLINK_PORT_FLAVOUR_UNUSED, /* Port which exists in the switch, but
+				      * is not used in any way.
+				      */
 };
 
 enum devlink_param_cmode {

net/core/devlink.c

@@ -7612,7 +7612,8 @@ static bool devlink_port_type_should_warn(struct devlink_port *devlink_port)
 {
 	/* Ignore CPU and DSA flavours. */
 	return devlink_port->attrs.flavour != DEVLINK_PORT_FLAVOUR_CPU &&
-	       devlink_port->attrs.flavour != DEVLINK_PORT_FLAVOUR_DSA;
+	       devlink_port->attrs.flavour != DEVLINK_PORT_FLAVOUR_DSA &&
+	       devlink_port->attrs.flavour != DEVLINK_PORT_FLAVOUR_UNUSED;
 }
 
 #define DEVLINK_PORT_TYPE_WARN_TIMEOUT (HZ * 3600)
@@ -7897,6 +7898,7 @@ static int __devlink_port_phys_port_name_get(struct devlink_port *devlink_port,
 		break;
 	case DEVLINK_PORT_FLAVOUR_CPU:
 	case DEVLINK_PORT_FLAVOUR_DSA:
+	case DEVLINK_PORT_FLAVOUR_UNUSED:
 		/* As CPU and DSA ports do not have a netdevice associated
 		 * case should not ever happen.
 		 */