To rehash a previous explanation given in commit 1c44ce56 ("net:
mscc: ocelot: fix vlan_filtering when enslaving to bridge before link is
up"), the switch driver operates the in a mode where a single VLAN can
be transmitted as untagged on a particular egress port. That is the
"native VLAN on trunk port" use case.

The configuration for this native VLAN is driven in 2 ways:
 - Set the egress port rewriter to strip the VLAN tag for the native
   VID (as it is egress-untagged, after all).
 - Configure the ingress port to drop untagged and priority-tagged
   traffic, if there is no native VLAN. The intention of this setting is
   that a trunk port with no native VLAN should not accept untagged
   traffic.

Since both of the above configurations for the native VLAN should only
be done if VLAN awareness is requested, they are actually done from the
ocelot_port_vlan_filtering function, after the basic procedure of
toggling the VLAN awareness flag of the port.

But there's a problem with that simplistic approach: we are trying to
juggle with 2 independent variables from a single function:
 - Native VLAN of the port - its value is held in port->vid.
 - VLAN awareness state of the port - currently there are some issues
   here, more on that later*.
The actual problem can be seen when enslaving the switch ports to a VLAN
filtering bridge:
 0. The driver configures a pvid of zero for each port, when in
    standalone mode. While the bridge configures a default_pvid of 1 for
    each port that gets added as a slave to it.
 1. The bridge calls ocelot_port_vlan_filtering with vlan_aware=true.
    The VLAN-filtering-dependent portion of the native VLAN
    configuration is done, considering that the native VLAN is 0.
 2. The bridge calls ocelot_vlan_add with vid=1, pvid=true,
    untagged=true. The native VLAN changes to 1 (change which gets
    propagated to hardware).
 3. ??? - nobody calls ocelot_port_vlan_filtering again, to reapply the
    VLAN-filtering-dependent portion of the native VLAN configuration,
    for the new native VLAN of 1. One can notice that after toggling "ip
    link set dev br0 type bridge vlan_filtering 0 && ip link set dev br0
    type bridge vlan_filtering 1", the new native VLAN finally makes it
    through and untagged traffic finally starts flowing again. But
    obviously that shouldn't be needed.

So it is clear that 2 independent variables need to both re-trigger the
native VLAN configuration. So we introduce the second variable as
ocelot_port->vlan_aware.

*Actually both the DSA Felix driver and the Ocelot driver already had
each its own variable:
 - Ocelot: ocelot_port_private->vlan_aware
 - Felix: dsa_port->vlan_filtering
but the common Ocelot library needs to work with a single, common,
variable, so there is some refactoring done to move the vlan_aware
property from the private structure into the common ocelot_port
structure.

Fixes: 97bb69e1 ("net: mscc: ocelot: break apart ocelot_vlan_port_apply")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>