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docs: net: dsa: sja1105: update list of limitations
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Remove the paragraphs that talk about the various modes of traffic
support, bridging with foreign interfaces, etc etc. There is nothing
that the user needs to know now, it should all work out of the box as
expected.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Vladimir Oltean authored and David S. Miller committed Aug 22, 2021
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218 changes: 1 addition & 217 deletions Documentation/networking/dsa/sja1105.rst
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Expand Up @@ -65,199 +65,6 @@ If that changed setting can be transmitted to the switch through the dynamic
reconfiguration interface, it is; otherwise the switch is reset and
reprogrammed with the updated static configuration.

Traffic support
===============

The switches do not have hardware support for DSA tags, except for "slow
protocols" for switch control as STP and PTP. For these, the switches have two
programmable filters for link-local destination MACs.
These are used to trap BPDUs and PTP traffic to the master netdevice, and are
further used to support STP and 1588 ordinary clock/boundary clock
functionality. For frames trapped to the CPU, source port and switch ID
information is encoded by the hardware into the frames.

But by leveraging ``CONFIG_NET_DSA_TAG_8021Q`` (a software-defined DSA tagging
format based on VLANs), general-purpose traffic termination through the network
stack can be supported under certain circumstances.

Depending on VLAN awareness state, the following operating modes are possible
with the switch:

- Mode 1 (VLAN-unaware): a port is in this mode when it is used as a standalone
net device, or when it is enslaved to a bridge with ``vlan_filtering=0``.
- Mode 2 (fully VLAN-aware): a port is in this mode when it is enslaved to a
bridge with ``vlan_filtering=1``. Access to the entire VLAN range is given to
the user through ``bridge vlan`` commands, but general-purpose (anything
other than STP, PTP etc) traffic termination is not possible through the
switch net devices. The other packets can be still by user space processed
through the DSA master interface (similar to ``DSA_TAG_PROTO_NONE``).
- Mode 3 (best-effort VLAN-aware): a port is in this mode when enslaved to a
bridge with ``vlan_filtering=1``, and the devlink property of its parent
switch named ``best_effort_vlan_filtering`` is set to ``true``. When
configured like this, the range of usable VIDs is reduced (0 to 1023 and 3072
to 4094), so is the number of usable VIDs (maximum of 7 non-pvid VLANs per
port*), and shared VLAN learning is performed (FDB lookup is done only by
DMAC, not also by VID).

To summarize, in each mode, the following types of traffic are supported over
the switch net devices:

+-------------+-----------+--------------+------------+
| | Mode 1 | Mode 2 | Mode 3 |
+=============+===========+==============+============+
| Regular | Yes | No | Yes |
| traffic | | (use master) | |
+-------------+-----------+--------------+------------+
| Management | Yes | Yes | Yes |
| traffic | | | |
| (BPDU, PTP) | | | |
+-------------+-----------+--------------+------------+

To configure the switch to operate in Mode 3, the following steps can be
followed::

ip link add dev br0 type bridge
# swp2 operates in Mode 1 now
ip link set dev swp2 master br0
# swp2 temporarily moves to Mode 2
ip link set dev br0 type bridge vlan_filtering 1
[ 61.204770] sja1105 spi0.1: Reset switch and programmed static config. Reason: VLAN filtering
[ 61.239944] sja1105 spi0.1: Disabled switch tagging
# swp3 now operates in Mode 3
devlink dev param set spi/spi0.1 name best_effort_vlan_filtering value true cmode runtime
[ 64.682927] sja1105 spi0.1: Reset switch and programmed static config. Reason: VLAN filtering
[ 64.711925] sja1105 spi0.1: Enabled switch tagging
# Cannot use VLANs in range 1024-3071 while in Mode 3.
bridge vlan add dev swp2 vid 1025 untagged pvid
RTNETLINK answers: Operation not permitted
bridge vlan add dev swp2 vid 100
bridge vlan add dev swp2 vid 101 untagged
bridge vlan
port vlan ids
swp5 1 PVID Egress Untagged

swp2 1 PVID Egress Untagged
100
101 Egress Untagged

swp3 1 PVID Egress Untagged

swp4 1 PVID Egress Untagged

br0 1 PVID Egress Untagged
bridge vlan add dev swp2 vid 102
bridge vlan add dev swp2 vid 103
bridge vlan add dev swp2 vid 104
bridge vlan add dev swp2 vid 105
bridge vlan add dev swp2 vid 106
bridge vlan add dev swp2 vid 107
# Cannot use mode than 7 VLANs per port while in Mode 3.
[ 3885.216832] sja1105 spi0.1: No more free subvlans

\* "maximum of 7 non-pvid VLANs per port": Decoding VLAN-tagged packets on the
CPU in mode 3 is possible through VLAN retagging of packets that go from the
switch to the CPU. In cross-chip topologies, the port that goes to the CPU
might also go to other switches. In that case, those other switches will see
only a retagged packet (which only has meaning for the CPU). So if they are
interested in this VLAN, they need to apply retagging in the reverse direction,
to recover the original value from it. This consumes extra hardware resources
for this switch. There is a maximum of 32 entries in the Retagging Table of
each switch device.

As an example, consider this cross-chip topology::

+-------------------------------------------------+
| Host SoC |
| +-------------------------+ |
| | DSA master for embedded | |
| | switch (non-sja1105) | |
| +--------+-------------------------+--------+ |
| | embedded L2 switch | |
| | | |
| | +--------------+ +--------------+ | |
| | |DSA master for| |DSA master for| | |
| | | SJA1105 1 | | SJA1105 2 | | |
+--+---+--------------+-----+--------------+---+--+

+-----------------------+ +-----------------------+
| SJA1105 switch 1 | | SJA1105 switch 2 |
+-----+-----+-----+-----+ +-----+-----+-----+-----+
|sw1p0|sw1p1|sw1p2|sw1p3| |sw2p0|sw2p1|sw2p2|sw2p3|
+-----+-----+-----+-----+ +-----+-----+-----+-----+

To reach the CPU, SJA1105 switch 1 (spi/spi2.1) uses the same port as is uses
to reach SJA1105 switch 2 (spi/spi2.2), which would be port 4 (not drawn).
Similarly for SJA1105 switch 2.

Also consider the following commands, that add VLAN 100 to every sja1105 user
port::

devlink dev param set spi/spi2.1 name best_effort_vlan_filtering value true cmode runtime
devlink dev param set spi/spi2.2 name best_effort_vlan_filtering value true cmode runtime
ip link add dev br0 type bridge
for port in sw1p0 sw1p1 sw1p2 sw1p3 \
sw2p0 sw2p1 sw2p2 sw2p3; do
ip link set dev $port master br0
done
ip link set dev br0 type bridge vlan_filtering 1
for port in sw1p0 sw1p1 sw1p2 sw1p3 \
sw2p0 sw2p1 sw2p2; do
bridge vlan add dev $port vid 100
done
ip link add link br0 name br0.100 type vlan id 100 && ip link set dev br0.100 up
ip addr add 192.168.100.3/24 dev br0.100
bridge vlan add dev br0 vid 100 self

bridge vlan
port vlan ids
sw1p0 1 PVID Egress Untagged
100

sw1p1 1 PVID Egress Untagged
100

sw1p2 1 PVID Egress Untagged
100

sw1p3 1 PVID Egress Untagged
100

sw2p0 1 PVID Egress Untagged
100

sw2p1 1 PVID Egress Untagged
100

sw2p2 1 PVID Egress Untagged
100

sw2p3 1 PVID Egress Untagged

br0 1 PVID Egress Untagged
100

SJA1105 switch 1 consumes 1 retagging entry for each VLAN on each user port
towards the CPU. It also consumes 1 retagging entry for each non-pvid VLAN that
it is also interested in, which is configured on any port of any neighbor
switch.

In this case, SJA1105 switch 1 consumes a total of 11 retagging entries, as
follows:

- 8 retagging entries for VLANs 1 and 100 installed on its user ports
(``sw1p0`` - ``sw1p3``)
- 3 retagging entries for VLAN 100 installed on the user ports of SJA1105
switch 2 (``sw2p0`` - ``sw2p2``), because it also has ports that are
interested in it. The VLAN 1 is a pvid on SJA1105 switch 2 and does not need
reverse retagging.

SJA1105 switch 2 also consumes 11 retagging entries, but organized as follows:

- 7 retagging entries for the bridge VLANs on its user ports (``sw2p0`` -
``sw2p3``).
- 4 retagging entries for VLAN 100 installed on the user ports of SJA1105
switch 1 (``sw1p0`` - ``sw1p3``).

Switching features
==================

Expand All @@ -282,33 +89,10 @@ untagged), and therefore this mode is also supported.

Segregating the switch ports in multiple bridges is supported (e.g. 2 + 2), but
all bridges should have the same level of VLAN awareness (either both have
``vlan_filtering`` 0, or both 1). Also an inevitable limitation of the fact
that VLAN awareness is global at the switch level is that once a bridge with
``vlan_filtering`` enslaves at least one switch port, the other un-bridged
ports are no longer available for standalone traffic termination.
``vlan_filtering`` 0, or both 1).

Topology and loop detection through STP is supported.

L2 FDB manipulation (add/delete/dump) is currently possible for the first
generation devices. Aging time of FDB entries, as well as enabling fully static
management (no address learning and no flooding of unknown traffic) is not yet
configurable in the driver.

A special comment about bridging with other netdevices (illustrated with an
example):

A board has eth0, eth1, swp0@eth1, swp1@eth1, swp2@eth1, swp3@eth1.
The switch ports (swp0-3) are under br0.
It is desired that eth0 is turned into another switched port that communicates
with swp0-3.

If br0 has vlan_filtering 0, then eth0 can simply be added to br0 with the
intended results.
If br0 has vlan_filtering 1, then a new br1 interface needs to be created that
enslaves eth0 and eth1 (the DSA master of the switch ports). This is because in
this mode, the switch ports beneath br0 are not capable of regular traffic, and
are only used as a conduit for switchdev operations.

Offloads
========

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