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Vladimir Oltean says:

====================
Update DSA documentation

These are some updates of dsa.rst, since it hasn't kept up with
development (in some cases, even since 2017). I've added Fixes: tags as
I thought was appropriate.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2022-07-18 12:44:37 +01:00
commit c32349f325
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Documentation/networking/dsa/dsa.rst
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@ -503,26 +503,108 @@ per-port PHY specific details: interface connection, MDIO bus location, etc.
Driver development
==================
DSA switch drivers need to implement a dsa_switch_ops structure which will
DSA switch drivers need to implement a ``dsa_switch_ops`` structure which will
contain the various members described below.
``register_switch_driver()`` registers this dsa_switch_ops in its internal list
of drivers to probe for. ``unregister_switch_driver()`` does the exact opposite.
Probing, registration and device lifetime
-----------------------------------------
Unless requested differently by setting the priv_size member accordingly, DSA
does not allocate any driver private context space.
DSA switches are regular ``device`` structures on buses (be they platform, SPI,
I2C, MDIO or otherwise). The DSA framework is not involved in their probing
with the device core.
Switch registration from the perspective of a driver means passing a valid
``struct dsa_switch`` pointer to ``dsa_register_switch()``, usually from the
switch driver's probing function. The following members must be valid in the
provided structure:
- ``ds->dev``: will be used to parse the switch's OF node or platform data.
- ``ds->num_ports``: will be used to create the port list for this switch, and
to validate the port indices provided in the OF node.
- ``ds->ops``: a pointer to the ``dsa_switch_ops`` structure holding the DSA
method implementations.
- ``ds->priv``: backpointer to a driver-private data structure which can be
retrieved in all further DSA method callbacks.
In addition, the following flags in the ``dsa_switch`` structure may optionally
be configured to obtain driver-specific behavior from the DSA core. Their
behavior when set is documented through comments in ``include/net/dsa.h``.
- ``ds->vlan_filtering_is_global``
- ``ds->needs_standalone_vlan_filtering``
- ``ds->configure_vlan_while_not_filtering``
- ``ds->untag_bridge_pvid``
- ``ds->assisted_learning_on_cpu_port``
- ``ds->mtu_enforcement_ingress``
- ``ds->fdb_isolation``
Internally, DSA keeps an array of switch trees (group of switches) global to
the kernel, and attaches a ``dsa_switch`` structure to a tree on registration.
The tree ID to which the switch is attached is determined by the first u32
number of the ``dsa,member`` property of the switch's OF node (0 if missing).
The switch ID within the tree is determined by the second u32 number of the
same OF property (0 if missing). Registering multiple switches with the same
switch ID and tree ID is illegal and will cause an error. Using platform data,
a single switch and a single switch tree is permitted.
In case of a tree with multiple switches, probing takes place asymmetrically.
The first N-1 callers of ``dsa_register_switch()`` only add their ports to the
port list of the tree (``dst->ports``), each port having a backpointer to its
associated switch (``dp->ds``). Then, these switches exit their
``dsa_register_switch()`` call early, because ``dsa_tree_setup_routing_table()``
has determined that the tree is not yet complete (not all ports referenced by
DSA links are present in the tree's port list). The tree becomes complete when
the last switch calls ``dsa_register_switch()``, and this triggers the effective
continuation of initialization (including the call to ``ds->ops->setup()``) for
all switches within that tree, all as part of the calling context of the last
switch's probe function.
The opposite of registration takes place when calling ``dsa_unregister_switch()``,
which removes a switch's ports from the port list of the tree. The entire tree
is torn down when the first switch unregisters.
It is mandatory for DSA switch drivers to implement the ``shutdown()`` callback
of their respective bus, and call ``dsa_switch_shutdown()`` from it (a minimal
version of the full teardown performed by ``dsa_unregister_switch()``).
The reason is that DSA keeps a reference on the master net device, and if the
driver for the master device decides to unbind on shutdown, DSA's reference
will block that operation from finalizing.
Either ``dsa_switch_shutdown()`` or ``dsa_unregister_switch()`` must be called,
but not both, and the device driver model permits the bus' ``remove()`` method
to be called even if ``shutdown()`` was already called. Therefore, drivers are
expected to implement a mutual exclusion method between ``remove()`` and
``shutdown()`` by setting their drvdata to NULL after any of these has run, and
checking whether the drvdata is NULL before proceeding to take any action.
After ``dsa_switch_shutdown()`` or ``dsa_unregister_switch()`` was called, no
further callbacks via the provided ``dsa_switch_ops`` may take place, and the
driver may free the data structures associated with the ``dsa_switch``.
Switch configuration
--------------------
- ``tag_protocol``: this is to indicate what kind of tagging protocol is supported,
should be a valid value from the ``dsa_tag_protocol`` enum
- ``get_tag_protocol``: this is to indicate what kind of tagging protocol is
supported, should be a valid value from the ``dsa_tag_protocol`` enum.
The returned information does not have to be static; the driver is passed the
CPU port number, as well as the tagging protocol of a possibly stacked
upstream switch, in case there are hardware limitations in terms of supported
tag formats.
- ``probe``: probe routine which will be invoked by the DSA platform device upon
registration to test for the presence/absence of a switch device. For MDIO
devices, it is recommended to issue a read towards internal registers using
the switch pseudo-PHY and return whether this is a supported device. For other
buses, return a non-NULL string
- ``change_tag_protocol``: when the default tagging protocol has compatibility
problems with the master or other issues, the driver may support changing it
at runtime, either through a device tree property or through sysfs. In that
case, further calls to ``get_tag_protocol`` should report the protocol in
current use.
- ``setup``: setup function for the switch, this function is responsible for setting
up the ``dsa_switch_ops`` private structure with all it needs: register maps,
@ -535,7 +617,17 @@ Switch configuration
fully configured and ready to serve any kind of request. It is recommended
to issue a software reset of the switch during this setup function in order to
avoid relying on what a previous software agent such as a bootloader/firmware
may have previously configured.
may have previously configured. The method responsible for undoing any
applicable allocations or operations done here is ``teardown``.
- ``port_setup`` and ``port_teardown``: methods for initialization and
destruction of per-port data structures. It is mandatory for some operations
such as registering and unregistering devlink port regions to be done from
these methods, otherwise they are optional. A port will be torn down only if
it has been previously set up. It is possible for a port to be set up during
probing only to be torn down immediately afterwards, for example in case its
PHY cannot be found. In this case, probing of the DSA switch continues
without that particular port.
PHY devices and link management
-------------------------------
@ -635,26 +727,198 @@ Power management
``BR_STATE_DISABLED`` and propagating changes to the hardware if this port is
disabled while being a bridge member
Address databases
-----------------
Switching hardware is expected to have a table for FDB entries, however not all
of them are active at the same time. An address database is the subset (partition)
of FDB entries that is active (can be matched by address learning on RX, or FDB
lookup on TX) depending on the state of the port. An address database may
occasionally be called "FID" (Filtering ID) in this document, although the
underlying implementation may choose whatever is available to the hardware.
For example, all ports that belong to a VLAN-unaware bridge (which is
*currently* VLAN-unaware) are expected to learn source addresses in the
database associated by the driver with that bridge (and not with other
VLAN-unaware bridges). During forwarding and FDB lookup, a packet received on a
VLAN-unaware bridge port should be able to find a VLAN-unaware FDB entry having
the same MAC DA as the packet, which is present on another port member of the
same bridge. At the same time, the FDB lookup process must be able to not find
an FDB entry having the same MAC DA as the packet, if that entry points towards
a port which is a member of a different VLAN-unaware bridge (and is therefore
associated with a different address database).
Similarly, each VLAN of each offloaded VLAN-aware bridge should have an
associated address database, which is shared by all ports which are members of
that VLAN, but not shared by ports belonging to different bridges that are
members of the same VID.
In this context, a VLAN-unaware database means that all packets are expected to
match on it irrespective of VLAN ID (only MAC address lookup), whereas a
VLAN-aware database means that packets are supposed to match based on the VLAN
ID from the classified 802.1Q header (or the pvid if untagged).
At the bridge layer, VLAN-unaware FDB entries have the special VID value of 0,
whereas VLAN-aware FDB entries have non-zero VID values. Note that a
VLAN-unaware bridge may have VLAN-aware (non-zero VID) FDB entries, and a
VLAN-aware bridge may have VLAN-unaware FDB entries. As in hardware, the
software bridge keeps separate address databases, and offloads to hardware the
FDB entries belonging to these databases, through switchdev, asynchronously
relative to the moment when the databases become active or inactive.
When a user port operates in standalone mode, its driver should configure it to
use a separate database called a port private database. This is different from
the databases described above, and should impede operation as standalone port
(packet in, packet out to the CPU port) as little as possible. For example,
on ingress, it should not attempt to learn the MAC SA of ingress traffic, since
learning is a bridging layer service and this is a standalone port, therefore
it would consume useless space. With no address learning, the port private
database should be empty in a naive implementation, and in this case, all
received packets should be trivially flooded to the CPU port.
DSA (cascade) and CPU ports are also called "shared" ports because they service
multiple address databases, and the database that a packet should be associated
to is usually embedded in the DSA tag. This means that the CPU port may
simultaneously transport packets coming from a standalone port (which were
classified by hardware in one address database), and from a bridge port (which
were classified to a different address database).
Switch drivers which satisfy certain criteria are able to optimize the naive
configuration by removing the CPU port from the flooding domain of the switch,
and just program the hardware with FDB entries pointing towards the CPU port
for which it is known that software is interested in those MAC addresses.
Packets which do not match a known FDB entry will not be delivered to the CPU,
which will save CPU cycles required for creating an skb just to drop it.
DSA is able to perform host address filtering for the following kinds of
addresses:
- Primary unicast MAC addresses of ports (``dev->dev_addr``). These are
associated with the port private database of the respective user port,
and the driver is notified to install them through ``port_fdb_add`` towards
the CPU port.
- Secondary unicast and multicast MAC addresses of ports (addresses added
through ``dev_uc_add()`` and ``dev_mc_add()``). These are also associated
with the port private database of the respective user port.
- Local/permanent bridge FDB entries (``BR_FDB_LOCAL``). These are the MAC
addresses of the bridge ports, for which packets must be terminated locally
and not forwarded. They are associated with the address database for that
bridge.
- Static bridge FDB entries installed towards foreign (non-DSA) interfaces
present in the same bridge as some DSA switch ports. These are also
associated with the address database for that bridge.
- Dynamically learned FDB entries on foreign interfaces present in the same
bridge as some DSA switch ports, only if ``ds->assisted_learning_on_cpu_port``
is set to true by the driver. These are associated with the address database
for that bridge.
For various operations detailed below, DSA provides a ``dsa_db`` structure
which can be of the following types:
- ``DSA_DB_PORT``: the FDB (or MDB) entry to be installed or deleted belongs to
the port private database of user port ``db->dp``.
- ``DSA_DB_BRIDGE``: the entry belongs to one of the address databases of bridge
``db->bridge``. Separation between the VLAN-unaware database and the per-VID
databases of this bridge is expected to be done by the driver.
- ``DSA_DB_LAG``: the entry belongs to the address database of LAG ``db->lag``.
Note: ``DSA_DB_LAG`` is currently unused and may be removed in the future.
The drivers which act upon the ``dsa_db`` argument in ``port_fdb_add``,
``port_mdb_add`` etc should declare ``ds->fdb_isolation`` as true.
DSA associates each offloaded bridge and each offloaded LAG with a one-based ID
(``struct dsa_bridge :: num``, ``struct dsa_lag :: id``) for the purposes of
refcounting addresses on shared ports. Drivers may piggyback on DSA's numbering
scheme (the ID is readable through ``db->bridge.num`` and ``db->lag.id`` or may
implement their own.
Only the drivers which declare support for FDB isolation are notified of FDB
entries on the CPU port belonging to ``DSA_DB_PORT`` databases.
For compatibility/legacy reasons, ``DSA_DB_BRIDGE`` addresses are notified to
drivers even if they do not support FDB isolation. However, ``db->bridge.num``
and ``db->lag.id`` are always set to 0 in that case (to denote the lack of
isolation, for refcounting purposes).
Note that it is not mandatory for a switch driver to implement physically
separate address databases for each standalone user port. Since FDB entries in
the port private databases will always point to the CPU port, there is no risk
for incorrect forwarding decisions. In this case, all standalone ports may
share the same database, but the reference counting of host-filtered addresses
(not deleting the FDB entry for a port's MAC address if it's still in use by
another port) becomes the responsibility of the driver, because DSA is unaware
that the port databases are in fact shared. This can be achieved by calling
``dsa_fdb_present_in_other_db()`` and ``dsa_mdb_present_in_other_db()``.
The down side is that the RX filtering lists of each user port are in fact
shared, which means that user port A may accept a packet with a MAC DA it
shouldn't have, only because that MAC address was in the RX filtering list of
user port B. These packets will still be dropped in software, however.
Bridge layer
------------
Offloading the bridge forwarding plane is optional and handled by the methods
below. They may be absent, return -EOPNOTSUPP, or ``ds->max_num_bridges`` may
be non-zero and exceeded, and in this case, joining a bridge port is still
possible, but the packet forwarding will take place in software, and the ports
under a software bridge must remain configured in the same way as for
standalone operation, i.e. have all bridging service functions (address
learning etc) disabled, and send all received packets to the CPU port only.
Concretely, a port starts offloading the forwarding plane of a bridge once it
returns success to the ``port_bridge_join`` method, and stops doing so after
``port_bridge_leave`` has been called. Offloading the bridge means autonomously
learning FDB entries in accordance with the software bridge port's state, and
autonomously forwarding (or flooding) received packets without CPU intervention.
This is optional even when offloading a bridge port. Tagging protocol drivers
are expected to call ``dsa_default_offload_fwd_mark(skb)`` for packets which
have already been autonomously forwarded in the forwarding domain of the
ingress switch port. DSA, through ``dsa_port_devlink_setup()``, considers all
switch ports part of the same tree ID to be part of the same bridge forwarding
domain (capable of autonomous forwarding to each other).
Offloading the TX forwarding process of a bridge is a distinct concept from
simply offloading its forwarding plane, and refers to the ability of certain
driver and tag protocol combinations to transmit a single skb coming from the
bridge device's transmit function to potentially multiple egress ports (and
thereby avoid its cloning in software).
Packets for which the bridge requests this behavior are called data plane
packets and have ``skb->offload_fwd_mark`` set to true in the tag protocol
driver's ``xmit`` function. Data plane packets are subject to FDB lookup,
hardware learning on the CPU port, and do not override the port STP state.
Additionally, replication of data plane packets (multicast, flooding) is
handled in hardware and the bridge driver will transmit a single skb for each
packet that may or may not need replication.
When the TX forwarding offload is enabled, the tag protocol driver is
responsible to inject packets into the data plane of the hardware towards the
correct bridging domain (FID) that the port is a part of. The port may be
VLAN-unaware, and in this case the FID must be equal to the FID used by the
driver for its VLAN-unaware address database associated with that bridge.
Alternatively, the bridge may be VLAN-aware, and in that case, it is guaranteed
that the packet is also VLAN-tagged with the VLAN ID that the bridge processed
this packet in. It is the responsibility of the hardware to untag the VID on
the egress-untagged ports, or keep the tag on the egress-tagged ones.
- ``port_bridge_join``: bridge layer function invoked when a given switch port is
added to a bridge, this function should do what's necessary at the switch
level to permit the joining port to be added to the relevant logical
domain for it to ingress/egress traffic with other members of the bridge.
By setting the ``tx_fwd_offload`` argument to true, the TX forwarding process
of this bridge is also offloaded.
- ``port_bridge_leave``: bridge layer function invoked when a given switch port is
removed from a bridge, this function should do what's necessary at the
switch level to deny the leaving port from ingress/egress traffic from the
remaining bridge members. When the port leaves the bridge, it should be aged
out at the switch hardware for the switch to (re) learn MAC addresses behind
this port.
remaining bridge members.
- ``port_stp_state_set``: bridge layer function invoked when a given switch port STP
state is computed by the bridge layer and should be propagated to switch
hardware to forward/block/learn traffic. The switch driver is responsible for
computing a STP state change based on current and asked parameters and perform
the relevant ageing based on the intersection results
hardware to forward/block/learn traffic.
- ``port_bridge_flags``: bridge layer function invoked when a port must
configure its settings for e.g. flooding of unknown traffic or source address
@ -667,21 +931,11 @@ Bridge layer
CPU port, and flooding towards the CPU port should also be enabled, due to a
lack of an explicit address filtering mechanism in the DSA core.
- ``port_bridge_tx_fwd_offload``: bridge layer function invoked after
``port_bridge_join`` when a driver sets ``ds->num_fwd_offloading_bridges`` to
a non-zero value. Returning success in this function activates the TX
forwarding offload bridge feature for this port, which enables the tagging
protocol driver to inject data plane packets towards the bridging domain that
the port is a part of. Data plane packets are subject to FDB lookup, hardware
learning on the CPU port, and do not override the port STP state.
Additionally, replication of data plane packets (multicast, flooding) is
handled in hardware and the bridge driver will transmit a single skb for each
packet that needs replication. The method is provided as a configuration
point for drivers that need to configure the hardware for enabling this
feature.
- ``port_bridge_tx_fwd_unoffload``: bridge layer function invoked when a driver
leaves a bridge port which had the TX forwarding offload feature enabled.
- ``port_fast_age``: bridge layer function invoked when flushing the
dynamically learned FDB entries on the port is necessary. This is called when
transitioning from an STP state where learning should take place to an STP
state where it shouldn't, or when leaving a bridge, or when address learning
is turned off via ``port_bridge_flags``.
Bridge VLAN filtering
---------------------
@ -697,55 +951,44 @@ Bridge VLAN filtering
allowed.
- ``port_vlan_add``: bridge layer function invoked when a VLAN is configured
(tagged or untagged) for the given switch port. If the operation is not
supported by the hardware, this function should return ``-EOPNOTSUPP`` to
inform the bridge code to fallback to a software implementation.
(tagged or untagged) for the given switch port. The CPU port becomes a member
of a VLAN only if a foreign bridge port is also a member of it (and
forwarding needs to take place in software), or the VLAN is installed to the
VLAN group of the bridge device itself, for termination purposes
(``bridge vlan add dev br0 vid 100 self``). VLANs on shared ports are
reference counted and removed when there is no user left. Drivers do not need
to manually install a VLAN on the CPU port.
- ``port_vlan_del``: bridge layer function invoked when a VLAN is removed from the
given switch port
- ``port_vlan_dump``: bridge layer function invoked with a switchdev callback
function that the driver has to call for each VLAN the given port is a member
of. A switchdev object is used to carry the VID and bridge flags.
- ``port_fdb_add``: bridge layer function invoked when the bridge wants to install a
Forwarding Database entry, the switch hardware should be programmed with the
specified address in the specified VLAN Id in the forwarding database
associated with this VLAN ID. If the operation is not supported, this
function should return ``-EOPNOTSUPP`` to inform the bridge code to fallback to
a software implementation.
.. note:: VLAN ID 0 corresponds to the port private database, which, in the context
of DSA, would be its port-based VLAN, used by the associated bridge device.
associated with this VLAN ID.
- ``port_fdb_del``: bridge layer function invoked when the bridge wants to remove a
Forwarding Database entry, the switch hardware should be programmed to delete
the specified MAC address from the specified VLAN ID if it was mapped into
this port forwarding database
- ``port_fdb_dump``: bridge layer function invoked with a switchdev callback
function that the driver has to call for each MAC address known to be behind
the given port. A switchdev object is used to carry the VID and FDB info.
- ``port_fdb_dump``: bridge bypass function invoked by ``ndo_fdb_dump`` on the
physical DSA port interfaces. Since DSA does not attempt to keep in sync its
hardware FDB entries with the software bridge, this method is implemented as
a means to view the entries visible on user ports in the hardware database.
The entries reported by this function have the ``self`` flag in the output of
the ``bridge fdb show`` command.
- ``port_mdb_add``: bridge layer function invoked when the bridge wants to install
a multicast database entry. If the operation is not supported, this function
should return ``-EOPNOTSUPP`` to inform the bridge code to fallback to a
software implementation. The switch hardware should be programmed with the
a multicast database entry. The switch hardware should be programmed with the
specified address in the specified VLAN ID in the forwarding database
associated with this VLAN ID.
.. note:: VLAN ID 0 corresponds to the port private database, which, in the context
of DSA, would be its port-based VLAN, used by the associated bridge device.
- ``port_mdb_del``: bridge layer function invoked when the bridge wants to remove a
multicast database entry, the switch hardware should be programmed to delete
the specified MAC address from the specified VLAN ID if it was mapped into
this port forwarding database.
- ``port_mdb_dump``: bridge layer function invoked with a switchdev callback
function that the driver has to call for each MAC address known to be behind
the given port. A switchdev object is used to carry the VID and MDB info.
Link aggregation
----------------