Introduced in commit 38b5beeae7a4 ("net: dsa: sja1105: prepare tagger
for handling DSA tags and VLAN simultaneously"), the sja1105_xmit_tpid
function solved quite a different problem than our needs are now.

Then, we used best-effort VLAN filtering and we were using the xmit_tpid
to tunnel packets coming from an 8021q upper through the TX VLAN allocated
by tag_8021q to that egress port. The need for a different VLAN protocol
depending on switch revision came from the fact that this in itself was
more of a hack to trick the hardware into accepting tunneled VLANs in
the first place.

Right now, we deny 8021q uppers (see sja1105_prechangeupper). Even if we
supported them again, we would not do that using the same method of
{tunneling the VLAN on egress, retagging the VLAN on ingress} that we
had in the best-effort VLAN filtering mode. It seems rather simpler that
we just allocate a VLAN in the VLAN table that is simply not used by the
bridge at all, or by any other port.

Anyway, I have 2 gripes with the current sja1105_xmit_tpid:

1. When sending packets on behalf of a VLAN-aware bridge (with the new
   TX forwarding offload framework) plus untagged (with the tag_8021q
   VLAN added by the tagger) packets, we can see that on SJA1105P/Q/R/S
   and later (which have a qinq_tpid of ETH_P_8021AD), some packets sent
   through the DSA master have a VLAN protocol of 0x8100 and others of
   0x88a8. This is strange and there is no reason for it now. If we have
   a bridge and are therefore forced to send using that bridge's TPID,
   we can as well blend with that bridge's VLAN protocol for all packets.

2. The sja1105_xmit_tpid introduces a dependency on the sja1105 driver,
   because it looks inside dp->priv. It is desirable to keep as much
   separation between taggers and switch drivers as possible. Now it
   doesn't do that anymore.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The sja1105 driver is a bit special in its use of VLAN headers as DSA
tags. This is because in VLAN-aware mode, the VLAN headers use an actual
TPID of 0x8100, which is understood even by the DSA master as an actual
VLAN header.

Furthermore, control packets such as PTP and STP are transmitted with no
VLAN header as a DSA tag, because, depending on switch generation, there
are ways to steer these control packets towards a precise egress port
other than VLAN tags. Transmitting control packets as untagged means
leaving a door open for traffic in general to be transmitted as untagged
from the DSA master, and for it to traverse the switch and exit a random
switch port according to the FDB lookup.

This behavior is a bit out of line with other DSA drivers which have
native support for DSA tagging. There, it is to be expected that the
switch only accepts DSA-tagged packets on its CPU port, dropping
everything that does not match this pattern.

We perhaps rely a bit too much on the switches' hardware dropping on the
CPU port, and place no other restrictions in the kernel data path to
avoid that. For example, sja1105 is also a bit special in that STP/PTP
packets are transmitted using "management routes"
(sja1105_port_deferred_xmit): when sending a link-local packet from the
CPU, we must first write a SPI message to the switch to tell it to
expect a packet towards multicast MAC DA 01-80-c2-00-00-0e, and to route
it towards port 3 when it gets it. This entry expires as soon as it
matches a packet received by the switch, and it needs to be reinstalled
for the next packet etc. All in all quite a ghetto mechanism, but it is
all that the sja1105 switches offer for injecting a control packet.
The driver takes a mutex for serializing control packets and making the
pairs of SPI writes of a management route and its associated skb atomic,
but to be honest, a mutex is only relevant as long as all parties agree
to take it. With the DSA design, it is possible to open an AF_PACKET
socket on the DSA master net device, and blast packets towards
01-80-c2-00-00-0e, and whatever locking the DSA switch driver might use,
it all goes kaput because management routes installed by the driver will
match skbs sent by the DSA master, and not skbs generated by the driver
itself. So they will end up being routed on the wrong port.

So through the lens of that, maybe it would make sense to avoid that
from happening by doing something in the network stack, like: introduce
a new bit in struct sk_buff, like xmit_from_dsa. Then, somewhere around
dev_hard_start_xmit(), introduce the following check:

	if (netdev_uses_dsa(dev) && !skb->xmit_from_dsa)
		kfree_skb(skb);

Ok, maybe that is a bit drastic, but that would at least prevent a bunch
of problems. For example, right now, even though the majority of DSA
switches drop packets without DSA tags sent by the DSA master (and
therefore the majority of garbage that user space daemons like avahi and
udhcpcd and friends create), it is still conceivable that an aggressive
user space program can open an AF_PACKET socket and inject a spoofed DSA
tag directly on the DSA master. We have no protection against that; the
packet will be understood by the switch and be routed wherever user
space says. Furthermore: there are some DSA switches where we even have
register access over Ethernet, using DSA tags. So even user space
drivers are possible in this way. This is a huge hole.

However, the biggest thing that bothers me is that udhcpcd attempts to
ask for an IP address on all interfaces by default, and with sja1105, it
will attempt to get a valid IP address on both the DSA master as well as
on sja1105 switch ports themselves. So with IP addresses in the same
subnet on multiple interfaces, the routing table will be messed up and
the system will be unusable for traffic until it is configured manually
to not ask for an IP address on the DSA master itself.

It turns out that it is possible to avoid that in the sja1105 driver, at
least very superficially, by requesting the switch to drop VLAN-untagged
packets on the CPU port. With the exception of control packets, all
traffic originated from tag_sja1105.c is already VLAN-tagged, so only
STP and PTP packets need to be converted. For that, we need to uphold
the equivalence between an untagged and a pvid-tagged packet, and to
remember that the CPU port of sja1105 uses a pvid of 4095.

Now that we drop untagged traffic on the CPU port, non-aggressive user
space applications like udhcpcd stop bothering us, and sja1105 effectively
becomes just as vulnerable to the aggressive kind of user space programs
as other DSA switches are (ok, users can also create 8021q uppers on top
of the DSA master in the case of sja1105, but in future patches we can
easily deny that, but it still doesn't change the fact that VLAN-tagged
packets can still be injected over raw sockets).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Add support for tag_sja1105 running on non-sja1105 DSA ports, by making
sure that every time we dereference dp->priv, we check the switch's
dsa_switch_ops (otherwise we access a struct sja1105_port structure that
is in fact something else).

This adds an unconditional build-time dependency between sja1105 being
built as module => tag_sja1105 must also be built as module. This was
there only for PTP before.

Some sane defaults must also take place when not running on sja1105
hardware. These are:

- sja1105_xmit_tpid: the sja1105 driver uses different VLAN protocols
  depending on VLAN awareness and switch revision (when an encapsulated
  VLAN must be sent). Default to 0x8100.

- sja1105_rcv_meta_state_machine: this aggregates PTP frames with their
  metadata timestamp frames. When running on non-sja1105 hardware, don't
  do that and accept all frames unmodified.

- sja1105_defer_xmit: calls sja1105_port_deferred_xmit in sja1105_main.c
  which writes a management route over SPI. When not running on sja1105
  hardware, bypass the SPI write and send the frame as-is.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The main desire for having this feature in sja1105 is to support network
stack termination for traffic coming from a VLAN-aware bridge.

For sja1105, offloading the bridge data plane means sending packets
as-is, with the proper VLAN tag, to the chip. The chip will look up its
FDB and forward them to the correct destination port.

But we support bridge data plane offload even for VLAN-unaware bridges,
and the implementation there is different. In fact, VLAN-unaware
bridging is governed by tag_8021q, so it makes sense to have the
.bridge_fwd_offload_add() implementation fully within tag_8021q.
The key difference is that we only support 1 VLAN-aware bridge, but we
support multiple VLAN-unaware bridges. So we need to make sure that the
forwarding domain is not crossed by packets injected from the stack.

For this, we introduce the concept of a tag_8021q TX VLAN for bridge
forwarding offload. As opposed to the regular TX VLANs which contain
only 2 ports (the user port and the CPU port), a bridge data plane TX
VLAN is "multicast" (or "imprecise"): it contains all the ports that are
part of a certain bridge, and the hardware will select where the packet
goes within this "imprecise" forwarding domain.

Each VLAN-unaware bridge has its own "imprecise" TX VLAN, so we make use
of the unique "bridge_num" provided by DSA for the data plane offload.
We use the same 3 bits from the tag_8021q VLAN ID format to encode this
bridge number.

Note that these 3 bit positions have been used before for sub-VLANs in
best-effort VLAN filtering mode. The difference is that for best-effort,
the sub-VLANs were only valid on RX (and it was documented that the
sub-VLAN field needed to be transmitted as zero). Whereas for the bridge
data plane offload, these 3 bits are only valid on TX.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The big problem which mandates cross-chip notifiers for tag_8021q is
this:

                                             |
    sw0p0     sw0p1     sw0p2     sw0p3     sw0p4
 [  user ] [  user ] [  user ] [  dsa  ] [  cpu  ]
                                   |
                                   +---------+
                                             |
    sw1p0     sw1p1     sw1p2     sw1p3     sw1p4
 [  user ] [  user ] [  user ] [  dsa  ] [  dsa  ]
                                   |
                                   +---------+
                                             |
    sw2p0     sw2p1     sw2p2     sw2p3     sw2p4
 [  user ] [  user ] [  user ] [  dsa  ] [  dsa  ]

When the user runs:

ip link add br0 type bridge
ip link set sw0p0 master br0
ip link set sw2p0 master br0

It doesn't work.

This is because dsa_8021q_crosschip_bridge_join() assumes that "ds" and
"other_ds" are at most 1 hop away from each other, so it is sufficient
to add the RX VLAN of {ds, port} into {other_ds, other_port} and vice
versa and presto, the cross-chip link works. When there is another
switch in the middle, such as in this case switch 1 with its DSA links
sw1p3 and sw1p4, somebody needs to tell it about these VLANs too.

Which is exactly why the problem is quadratic: when a port joins a
bridge, for each port in the tree that's already in that same bridge we
notify a tag_8021q VLAN addition of that port's RX VLAN to the entire
tree. It is a very complicated web of VLANs.

It must be mentioned that currently we install tag_8021q VLANs on too
many ports (DSA links - to be precise, on all of them). For example,
when sw2p0 joins br0, and assuming sw1p0 was part of br0 too, we add the
RX VLAN of sw2p0 on the DSA links of switch 0 too, even though there
isn't any port of switch 0 that is a member of br0 (at least yet).
In theory we could notify only the switches which sit in between the
port joining the bridge and the port reacting to that bridge_join event.
But in practice that is impossible, because of the way 'link' properties
are described in the device tree. The DSA bindings require DT writers to
list out not only the real/physical DSA links, but in fact the entire
routing table, like for example switch 0 above will have:

	sw0p3: port@3 {
		link = <&sw1p4 &sw2p4>;
	};

This was done because:

/* TODO: ideally DSA ports would have a single dp->link_dp member,
 * and no dst->rtable nor this struct dsa_link would be needed,
 * but this would require some more complex tree walking,
 * so keep it stupid at the moment and list them all.
 */

but it is a perfect example of a situation where too much information is
actively detrimential, because we are now in the position where we
cannot distinguish a real DSA link from one that is put there to avoid
the 'complex tree walking'. And because DT is ABI, there is not much we
can change.

And because we do not know which DSA links are real and which ones
aren't, we can't really know if DSA switch A is in the data path between
switches B and C, in the general case.

So this is why tag_8021q RX VLANs are added on all DSA links, and
probably why it will never change.

On the other hand, at least the number of additions/deletions is well
balanced, and this means that once we implement reference counting at
the cross-chip notifier level a la fdb/mdb, there is absolutely zero
need for a struct dsa_8021q_crosschip_link, it's all self-managing.

In fact, with the tag_8021q notifiers emitted from the bridge join
notifiers, it becomes so generic that sja1105 does not need to do
anything anymore, we can just delete its implementation of the
.crosschip_bridge_{join,leave} methods.

Among other things we can simply delete is the home-grown implementation
of sja1105_notify_crosschip_switches(). The reason why that is wrong is
because it is not quadratic - it only covers remote switches to which we
have a cross-chip bridging link and that does not cover in-between
switches. This deletion is part of the same patch because sja1105 used
to poke deep inside the guts of the tag_8021q context in order to do
that. Because the cross-chip links went away, so needs the sja1105 code.

Last but not least, dsa_8021q_setup_port() is simplified (and also
renamed). Because our TAG_8021Q_VLAN_ADD notifier is designed to react
on the CPU port too, the four dsa_8021q_vid_apply() calls:
- 1 for RX VLAN on user port
- 1 for the user port's RX VLAN on the CPU port
- 1 for TX VLAN on user port
- 1 for the user port's TX VLAN on the CPU port

now get squashed into only 2 notifier calls via
dsa_port_tag_8021q_vlan_add.

And because the notifiers to add and to delete a tag_8021q VLAN are
distinct, now we finally break up the port setup and teardown into
separate functions instead of relying on a "bool enabled" flag which
tells us what to do. Arguably it should have been this way from the
get go.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Right now, setting up tag_8021q is a 2-step operation for a driver,
first the context structure needs to be created, then the VLANs need to
be installed on the ports. A similar thing is true for teardown.

Merge the 2 steps into the register/unregister methods, to be as
transparent as possible for the driver as to what tag_8021q does behind
the scenes. This also gets rid of the funny "bool setup == true means
setup, == false means teardown" API that tag_8021q used to expose.

Note that dsa_tag_8021q_register() must be called at least in the
.setup() driver method and never earlier (like in the driver probe
function). This is because the DSA switch tree is not initialized at
probe time, and the cross-chip notifiers will not work.

For symmetry with .setup(), the unregister method should be put in
.teardown().

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Make tag_8021q a more central element of DSA and move the 2 driver
specific operations outside of struct dsa_8021q_context (which is
supposed to hold dynamic data and not really constant function
pointers).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The basic problem description is as follows:

Be there 3 switches in a daisy chain topology:

                                             |
    sw0p0     sw0p1     sw0p2     sw0p3     sw0p4
 [  user ] [  user ] [  user ] [  dsa  ] [  cpu  ]
                                   |
                                   +---------+
                                             |
    sw1p0     sw1p1     sw1p2     sw1p3     sw1p4
 [  user ] [  user ] [  user ] [  dsa  ] [  dsa  ]
                                   |
                                   +---------+
                                             |
    sw2p0     sw2p1     sw2p2     sw2p3     sw2p4
 [  user ] [  user ] [  user ] [  user ] [  dsa  ]

The CPU will not be able to ping through the user ports of the
bottom-most switch (like for example sw2p0), simply because tag_8021q
was not coded up for this scenario - it has always assumed DSA switch
trees with a single switch.

To add support for the topology above, we must admit that the RX VLAN of
sw2p0 must be added on some ports of switches 0 and 1 as well. This is
in fact a textbook example of thing that can use the cross-chip notifier
framework that DSA has set up in switch.c.

There is only one problem: core DSA (switch.c) is not able right now to
make the connection between a struct dsa_switch *ds and a struct
dsa_8021q_context *ctx. Right now, it is drivers who call into
tag_8021q.c and always provide a struct dsa_8021q_context *ctx pointer,
and tag_8021q.c calls them back with the .tag_8021q_vlan_{add,del}
methods.

But with cross-chip notifiers, it is possible for tag_8021q to call
drivers without drivers having ever asked for anything. A good example
is right above: when sw2p0 wants to set itself up for tag_8021q,
the .tag_8021q_vlan_add method needs to be called for switches 1 and 0,
so that they transport sw2p0's VLANs towards the CPU without dropping
them.

So instead of letting drivers manage the tag_8021q context, add a
tag_8021q_ctx pointer inside of struct dsa_switch, which will be
populated when dsa_tag_8021q_register() returns success.

The patch is fairly long-winded because we are partly reverting commit
5899ee367ab3 ("net: dsa: tag_8021q: add a context structure") which made
the driver-facing tag_8021q API use "ctx" instead of "ds". Now that we
can access "ctx" directly from "ds", this is no longer needed.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

In preparation of moving tag_8021q to core DSA, move all initialization
and teardown related to tag_8021q which is currently done by drivers in
2 functions called "register" and "unregister". These will gather more
functionality in future patches, which will better justify the chosen
naming scheme.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This is no longer necessary since tag_8021q doesn't register itself as a
full-blown tagger anymore.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>