networking/dsa/dsa.rst

5 This document describes the **Distributed Switch Architecture (DSA)** subsystem
13 The Distributed Switch Architecture subsystem was primarily designed to
14 support Marvell Ethernet switches (MV88E6xxx, a.k.a. Link Street product
19 they configured/queried a switch port network device or a regular network
22 An Ethernet switch typically comprises multiple front-panel ports and one
24 presence of a management port connected to an Ethernet controller capable of
25 receiving Ethernet frames from the switch. This is a very common setup for all
26 kinds of Ethernet switches found in Small Home and Office products: routers,
27 gateways, or even top-of-rack switches. This host Ethernet controller will
32 using upstream and downstream Ethernet links between switches. These specific
34 of multiple switches connected to each other is called a "switch tree".
36 For each front-panel port, DSA creates specialized network devices which are
37 used as controlling and data-flowing endpoints for use by the Linux networking
41 The ideal case for using DSA is when an Ethernet switch supports a "switch tag"
42 which is a hardware feature making the switch insert a specific tag for each
43 Ethernet frame it receives to/from specific ports to help the management
46 - what port is this frame coming from
47 - what was the reason why this frame got forwarded
48 - how to send CPU originated traffic to specific ports
52 on Port-based VLAN IDs).
57 - the "cpu" port is the Ethernet switch facing side of the management
61 - the "dsa" port(s) are just conduits between two or more switches, and as such
63   downstream, or the top-most upstream interface makes sense with that model
69 Switch tagging protocols
70 ------------------------
72 DSA supports many vendor-specific tagging protocols, one software-defined
73 tagging protocol, and a tag-less mode as well (``DSA_TAG_PROTO_NONE``).
78 - identifies which port the Ethernet frame came from/should be sent to
79 - provides a reason why this frame was forwarded to the management interface
86 1. The switch-specific frame header is located before the Ethernet header,
89 2. The switch-specific frame header is located before the EtherType, keeping
92 3. The switch-specific frame header is located at the tail of the packet,
96 A tagging protocol may tag all packets with switch tags of the same length, or
98 require an extended switch tag, or there might be one tag length on TX and a
101 with the length in octets of the longest switch frame header/trailer. The DSA
106 on a best-effort basis, the allocation of packets with enough extra space such
107 that the act of pushing the switch tag on transmission of a packet does not
110 Even though applications are not expected to parse DSA-specific frame headers,
115 characteristics of the interaction required between the switch hardware and the
121 switch tree use the same tagging protocol. In case of a packet transiting a
122 fabric with more than one switch, the switch-specific frame header is inserted
123 by the first switch in the fabric that the packet was received on. This header
128 other switches from the same fabric, and in this case, the outermost switch
132 by a leaf switch (not connected directly to the CPU) is not the same as what
133 the network stack sees. This can be seen with Marvell switch trees, where the
137 It still remains the case that, if the DSA switch tree is configured for the
138 EDSA tagging protocol, the operating system sees EDSA-tagged packets from the
140 because the Marvell switch connected directly to the CPU is configured to
146 no DSA links in this fabric, and each switch constitutes a disjoint DSA switch
147 tree. The DSA links are viewed as simply a pair of a DSA conduit (the out-facing
148 port of the upstream DSA switch) and a CPU port (the in-facing port of the
149 downstream DSA switch).
151 The tagging protocol of the attached DSA switch tree can be viewed through the
156 If the hardware and driver are capable, the tagging protocol of the DSA switch
159 all attached switch ports must be down while doing this).
165 regardless of the driver used for the switch control path, and the driver used
169 The passed ``struct sk_buff *skb`` has ``skb->data`` pointing at
173 The job of this method is to prepare the skb in a way that the switch will
181 passed ``struct sk_buff *skb`` has ``skb->data`` pointing at
184 method is to consume the frame header, adjust ``skb->data`` to really point at
185 the first octet after the EtherType, and to change ``skb->dev`` to point to the
186 virtual DSA user network interface corresponding to the physical front-facing
187 switch port that the packet was received on.
211 already expect the switch tag in use, the checksum must be calculated before any
214 when the tag gets stripped by the switch during transmission, it will leave an
218 with DSA-unaware conduits, mangling what the conduit perceives as MAC DA), the
222 Note that this assumes a DSA-unaware conduit driver, which is the norm.
225 -----------------------
228 the CPU/management Ethernet interface. Such a driver might occasionally need to
234 Ethernet switch.
237 ----------------------
240 networking stack is in order to have the DSA subsystem process the Ethernet
241 switch specific tagging protocol. DSA accomplishes this by registering a
242 specific (and fake) Ethernet type (later becoming ``skb->protocol``) with the
244 Ethernet Frame receive sequence looks like this:
250         - receive function is invoked
251         - basic packet processing is done: getting length, status etc.
252         - packet is prepared to be processed by the Ethernet layer by calling
255 2. net/ethernet/eth.c::
258                   if (dev->dsa_ptr != NULL)
259                           -> skb->protocol = ETH_P_XDSA
261 3. drivers/net/ethernet/\*::
264                   -> iterate over registered packet_type
265                           -> invoke handler for ETH_P_XDSA, calls dsa_switch_rcv()
269           -> dsa_switch_rcv()
270                   -> invoke switch tag specific protocol handler in 'net/dsa/tag_*.c'
274         - inspect and strip switch tag protocol to determine originating port
275         - locate per-port network device
276         - invoke ``eth_type_trans()`` with the DSA user network device
277         - invoked ``netif_receive_skb()``
279 Past this point, the DSA user network devices get delivered regular Ethernet
283 --------------------
287 controlling and data-flowing end-point for each front-panel port of the switch.
290 - insert/remove the switch tag protocol (if it exists) when sending traffic
291   to/from specific switch ports
292 - query the switch for ethtool operations: statistics, link state,
293   Wake-on-LAN, register dumps...
294 - manage external/internal PHY: link, auto-negotiation, etc.
298 stack/ethtool and the switch driver implementation.
301 switch tagging protocol is currently registered with these network devices and
303 switch tag in the Ethernet frames.
306 ``ndo_start_xmit()`` function. Since they contain the appropriate switch tag, the
307 Ethernet switch will be able to process these incoming frames from the
308 management interface and deliver them to the physical switch port.
322 towards the switch.
325 ------------------------
334            +-----------v--|--------------------+
335            |+------+ +------+ +------+ +------+|
337            |+------+-+------+-+------+-+------+|
338            |          DSA switch driver        |
339            +-----------------------------------+
342            switch driver |        | switch driver
344            +-----------------------------------+
346    --------+-----------------------------------+------------
348            +-----------------------------------+
351          switch hardware |        | switch hardware
353            +-----------------------------------+
354            |               Switch              |
355            |+------+ +------+ +------+ +------+|
357            ++------+-+------+-+------+-+------++
360 -------------
362 In order to be able to read to/from a switch PHY built into it, DSA creates an
363 user MDIO bus which allows a specific switch driver to divert and intercept
364 MDIO reads/writes towards specific PHY addresses. In most MDIO-connected
366 to return standard MII registers from the switch builtin PHYs, allowing the PHY
367 library and/or to return link status, link partner pages, auto-negotiation
370 For Ethernet switches which have both external and internal MDIO buses, the
372 internal or external MDIO devices this switch might be connected to: internal
376 ---------------
381 - ``dsa_chip_data``: platform data configuration for a given switch device,
382   this structure describes a switch device's parent device, its address, as
386 - ``dsa_platform_data``: platform device configuration data which can reference
388   the conduit network device this switch tree is attached to needs to be
391 - ``dsa_switch_tree``: structure assigned to the conduit network device under
393   the tagging protocol supported by the switch tree, and which receive/transmit
395   switch is also provided: CPU port. Finally, a collection of dsa_switch are
398 - ``dsa_switch``: structure describing a switch device in the tree, referencing
402 - ``dsa_switch_ops``: structure referencing function pointers, see below for a
409 -------------------------------
414 - inability to fetch switch CPU port statistics counters using ethtool, which
415   can make it harder to debug MDIO switch connected using xMII interfaces
417 - inability to configure the CPU port link parameters based on the Ethernet
420 - inability to configure specific VLAN IDs / trunking VLANs between switches
424 --------------------------------
426 Once a conduit network device is configured to use DSA (dev->dsa_ptr becomes
427 non-NULL), and the switch behind it expects a tagging protocol, this network
430 will not make us go through the switch tagging protocol transmit function, so
431 the Ethernet switch on the other end, expecting a tag will typically drop this
439 - MDIO/PHY library: ``drivers/net/phy/phy.c``, ``mdio_bus.c``
440 - Switchdev:``net/switchdev/*``
441 - Device Tree for various of_* functions
442 - Devlink: ``net/core/devlink.c``
445 ----------------
451 - internal PHY devices, built into the Ethernet switch hardware
452 - external PHY devices, connected via an internal or external MDIO bus
453 - internal PHY devices, connected via an internal MDIO bus
454 - special, non-autonegotiated or non MDIO-managed PHY devices: SFPs, MoCA; a.k.a
460 - if Device Tree is used, the PHY device is looked up using the standard
461   "phy-handle" property, if found, this PHY device is created and registered
464 - if Device Tree is used and the PHY device is "fixed", that is, conforms to
465   the definition of a non-MDIO managed PHY as defined in
466   ``Documentation/devicetree/bindings/net/fixed-link.txt``, the PHY is registered
469 - finally, if the PHY is built into the switch, as is very common with
470   standalone switch packages, the PHY is probed using the user MII bus created
475 ---------
479 of per-port user network devices. As of today, the only SWITCHDEV objects
483 -------
485 DSA registers one devlink device per physical switch in the fabric.
491 - Regions: debugging feature which allows user space to dump driver-defined
492   areas of hardware information in a low-level, binary format. Both global
493   regions as well as per-port regions are supported. It is possible to export
495   to the standard iproute2 user space programs (ip-link, bridge), like address
497   contain additional hardware-specific details which are not visible through
499   the non-user ports too, which are invisible to iproute2 because no network
501 - Params: a feature which enables user to configure certain low-level tunable
503   devlink params, or may add new device-specific devlink params.
504 - Resources: a monitoring feature which enables users to see the degree of
506 - Shared buffers: a QoS feature for adjusting and partitioning memory and frame
508   directions, such that low-priority bulk traffic does not impede the
509   processing of high-priority critical traffic.
514 -----------
519 per-port PHY specific details: interface connection, MDIO bus location, etc.
524 DSA switch drivers need to implement a ``dsa_switch_ops`` structure which will
528 -----------------------------------------
534 Switch registration from the perspective of a driver means passing a valid
536 switch driver's probing function. The following members must be valid in the
539 - ``ds->dev``: will be used to parse the switch's OF node or platform data.
541 - ``ds->num_ports``: will be used to create the port list for this switch, and
544 - ``ds->ops``: a pointer to the ``dsa_switch_ops`` structure holding the DSA
547 - ``ds->priv``: backpointer to a driver-private data structure which can be
551 be configured to obtain driver-specific behavior from the DSA core. Their
554 - ``ds->vlan_filtering_is_global``
556 - ``ds->needs_standalone_vlan_filtering``
558 - ``ds->configure_vlan_while_not_filtering``
560 - ``ds->untag_bridge_pvid``
562 - ``ds->assisted_learning_on_cpu_port``
564 - ``ds->mtu_enforcement_ingress``
566 - ``ds->fdb_isolation``
568 Internally, DSA keeps an array of switch trees (group of switches) global to
570 The tree ID to which the switch is attached is determined by the first u32
571 number of the ``dsa,member`` property of the switch's OF node (0 if missing).
572 The switch ID within the tree is determined by the second u32 number of the
574 switch ID and tree ID is illegal and will cause an error. Using platform data,
575 a single switch and a single switch tree is permitted.
578 The first N-1 callers of ``dsa_register_switch()`` only add their ports to the
579 port list of the tree (``dst->ports``), each port having a backpointer to its
580 associated switch (``dp->ds``). Then, these switches exit their
584 the last switch calls ``dsa_register_switch()``, and this triggers the effective
585 continuation of initialization (including the call to ``ds->ops->setup()``) for
587 switch's probe function.
590 which removes a switch's ports from the port list of the tree. The entire tree
591 is torn down when the first switch unregisters.
593 It is mandatory for DSA switch drivers to implement the ``shutdown()`` callback
611 Switch configuration
612 --------------------
614 - ``get_tag_protocol``: this is to indicate what kind of tagging protocol is
618   upstream switch, in case there are hardware limitations in terms of supported
621 - ``change_tag_protocol``: when the default tagging protocol has compatibility
627 - ``setup``: setup function for the switch, this function is responsible for setting
630   configure the switch to separate all network interfaces from each other, that
631   is, they should be isolated by the switch hardware itself, typically by creating
632   a Port-based VLAN ID for each port and allowing only the CPU port and the
634   platform should be disabled. Past this function, the switch is expected to be
636   to issue a software reset of the switch during this setup function in order to
641 - ``port_setup`` and ``port_teardown``: methods for initialization and
642   destruction of per-port data structures. It is mandatory for some operations
647   PHY cannot be found. In this case, probing of the DSA switch continues
650 - ``port_change_conduit``: method through which the affinity (association used
659   conduit->dsa_ptr``. Additionally, the conduit can also be a LAG device where
661   valid ``conduit->dsa_ptr`` pointer, however this is not unique, but rather a
669 -------------------------------
671 - ``get_phy_flags``: Some switches are interfaced to various kinds of Ethernet PHYs,
673   on its own (e.g.: coming from switch memory mapped registers), this function
674   should return a 32-bit bitmask of "flags" that is private between the switch
675   driver and the Ethernet PHY driver in ``drivers/net/phy/\*``.
677 - ``phy_read``: Function invoked by the DSA user MDIO bus when attempting to read
678   the switch port MDIO registers. If unavailable, return 0xffff for each read.
679   For builtin switch Ethernet PHYs, this function should allow reading the link
680   status, auto-negotiation results, link partner pages, etc.
682 - ``phy_write``: Function invoked by the DSA user MDIO bus when attempting to write
683   to the switch port MDIO registers. If unavailable return a negative error
686 - ``adjust_link``: Function invoked by the PHY library when a user network device
688   configuring the switch port link parameters: speed, duplex, pause based on
691 - ``fixed_link_update``: Function invoked by the PHY library, and specifically by
692   the fixed PHY driver asking the switch driver for link parameters that could
693   not be auto-negotiated, or obtained by reading the PHY registers through MDIO.
695   MoCA or other kinds of non-MDIO managed PHYs where out of band link
699 ------------------
701 - ``get_strings``: ethtool function used to query the driver's strings, will
704 - ``get_ethtool_stats``: ethtool function used to query per-port statistics and
706   RX/TX counters from the network device, with switch driver specific statistics
709 - ``get_sset_count``: ethtool function used to query the number of statistics items
711 - ``get_wol``: ethtool function used to obtain Wake-on-LAN settings per-port, this
713   Wake-on-LAN settings if this interface needs to participate in Wake-on-LAN
715 - ``set_wol``: ethtool function used to configure Wake-on-LAN settings per-port,
718 - ``set_eee``: ethtool function which is used to configure a switch port EEE (Green
719   Ethernet) settings, can optionally invoke the PHY library to enable EEE at the
720   PHY level if relevant. This function should enable EEE at the switch port MAC
721   controller and data-processing logic
723 - ``get_eee``: ethtool function which is used to query a switch port EEE settings,
724   this function should return the EEE state of the switch port MAC controller
725   and data-processing logic as well as query the PHY for its currently configured
728 - ``get_eeprom_len``: ethtool function returning for a given switch the EEPROM
731 - ``get_eeprom``: ethtool function returning for a given switch the EEPROM contents
733 - ``set_eeprom``: ethtool function writing specified data to a given switch EEPROM
735 - ``get_regs_len``: ethtool function returning the register length for a given
736   switch
738 - ``get_regs``: ethtool function returning the Ethernet switch internal register
739   contents. This function might require user-land code in ethtool to
740   pretty-print register values and registers
743 ----------------
745 - ``suspend``: function invoked by the DSA platform device when the system goes to
746   suspend, should quiesce all Ethernet switch activities, but keep ports
747   participating in Wake-on-LAN active as well as additional wake-up logic if
750 - ``resume``: function invoked by the DSA platform device when the system resumes,
751   should resume all Ethernet switch activities and re-configure the switch to be
754 - ``port_enable``: function invoked by the DSA user network device ndo_open
756   fully enable a given switch port. DSA takes care of marking the port with
760 - ``port_disable``: function invoked by the DSA user network device ndo_close
762   fully disable a given switch port. DSA takes care of marking the port with
767 -----------------
776 For example, all ports that belong to a VLAN-unaware bridge (which is
777 *currently* VLAN-unaware) are expected to learn source addresses in the
779 VLAN-unaware bridges). During forwarding and FDB lookup, a packet received on a
780 VLAN-unaware bridge port should be able to find a VLAN-unaware FDB entry having
784 a port which is a member of a different VLAN-unaware bridge (and is therefore
787 Similarly, each VLAN of each offloaded VLAN-aware bridge should have an
792 In this context, a VLAN-unaware database means that all packets are expected to
794 VLAN-aware database means that packets are supposed to match based on the VLAN
797 At the bridge layer, VLAN-unaware FDB entries have the special VID value of 0,
798 whereas VLAN-aware FDB entries have non-zero VID values. Note that a
799 VLAN-unaware bridge may have VLAN-aware (non-zero VID) FDB entries, and a
800 VLAN-aware bridge may have VLAN-unaware FDB entries. As in hardware, the
822 Switch drivers which satisfy certain criteria are able to optimize the naive
823 configuration by removing the CPU port from the flooding domain of the switch,
832 - Primary unicast MAC addresses of ports (``dev->dev_addr``). These are
837 - Secondary unicast and multicast MAC addresses of ports (addresses added
841 - Local/permanent bridge FDB entries (``BR_FDB_LOCAL``). These are the MAC
846 - Static bridge FDB entries installed towards foreign (non-DSA) interfaces
847   present in the same bridge as some DSA switch ports. These are also
850 - Dynamically learned FDB entries on foreign interfaces present in the same
851   bridge as some DSA switch ports, only if ``ds->assisted_learning_on_cpu_port``
858 - ``DSA_DB_PORT``: the FDB (or MDB) entry to be installed or deleted belongs to
859   the port private database of user port ``db->dp``.
860 - ``DSA_DB_BRIDGE``: the entry belongs to one of the address databases of bridge
861   ``db->bridge``. Separation between the VLAN-unaware database and the per-VID
863 - ``DSA_DB_LAG``: the entry belongs to the address database of LAG ``db->lag``.
867 ``port_mdb_add`` etc should declare ``ds->fdb_isolation`` as true.
869 DSA associates each offloaded bridge and each offloaded LAG with a one-based ID
872 scheme (the ID is readable through ``db->bridge.num`` and ``db->lag.id`` or may
878 drivers even if they do not support FDB isolation. However, ``db->bridge.num``
879 and ``db->lag.id`` are always set to 0 in that case (to denote the lack of
882 Note that it is not mandatory for a switch driver to implement physically
886 share the same database, but the reference counting of host-filtered addresses
897 ------------
900 below. They may be absent, return -EOPNOTSUPP, or ``ds->max_num_bridges`` may
901 be non-zero and exceeded, and in this case, joining a bridge port is still
915 ingress switch port. DSA, through ``dsa_port_devlink_setup()``, considers all
916 switch ports part of the same tree ID to be part of the same bridge forwarding
926 packets and have ``skb->offload_fwd_mark`` set to true in the tag protocol
936 VLAN-unaware, and in this case the FID must be equal to the FID used by the
937 driver for its VLAN-unaware address database associated with that bridge.
938 Alternatively, the bridge may be VLAN-aware, and in that case, it is guaranteed
939 that the packet is also VLAN-tagged with the VLAN ID that the bridge processed
941 the egress-untagged ports, or keep the tag on the egress-tagged ones.
943 - ``port_bridge_join``: bridge layer function invoked when a given switch port is
944   added to a bridge, this function should do what's necessary at the switch
950 - ``port_bridge_leave``: bridge layer function invoked when a given switch port is
952   switch level to deny the leaving port from ingress/egress traffic from the
955 - ``port_stp_state_set``: bridge layer function invoked when a given switch port STP
956   state is computed by the bridge layer and should be propagated to switch
959 - ``port_bridge_flags``: bridge layer function invoked when a port must
961   learning. The switch driver is responsible for initial setup of the
970 - ``port_fast_age``: bridge layer function invoked when flushing the
977 ---------------------
979 - ``port_vlan_filtering``: bridge layer function invoked when the bridge gets
984   VLAN ID map/rules.  If there is no PVID programmed into the switch port,
985   untagged frames must be rejected as well. When turned off the switch must
989 - ``port_vlan_add``: bridge layer function invoked when a VLAN is configured
990   (tagged or untagged) for the given switch port. The CPU port becomes a member
998 - ``port_vlan_del``: bridge layer function invoked when a VLAN is removed from the
999   given switch port
1001 - ``port_fdb_add``: bridge layer function invoked when the bridge wants to install a
1002   Forwarding Database entry, the switch hardware should be programmed with the
1006 - ``port_fdb_del``: bridge layer function invoked when the bridge wants to remove a
1007   Forwarding Database entry, the switch hardware should be programmed to delete
1011 - ``port_fdb_dump``: bridge bypass function invoked by ``ndo_fdb_dump`` on the
1018 - ``port_mdb_add``: bridge layer function invoked when the bridge wants to install
1019   a multicast database entry. The switch hardware should be programmed with the
1023 - ``port_mdb_del``: bridge layer function invoked when the bridge wants to remove a
1024   multicast database entry, the switch hardware should be programmed to delete
1029 ----------------
1046 - ``port_lag_join``: function invoked when a given switch port is added to a
1047   LAG. The driver may return ``-EOPNOTSUPP``, and in this case, DSA will fall
1050 - ``port_lag_leave``: function invoked when a given switch port leaves a LAG
1052 - ``port_lag_change``: function invoked when the link state of any member of
1057 can optionally populate ``ds->num_lag_ids`` from the ``dsa_switch_ops::setup``
1059 retrieved by a DSA switch driver using the ``dsa_lag_id`` function.
1061 IEC 62439-2 (MRP)
1062 -----------------
1077 necessary for the hardware, even if it is not MRP-aware, to be able to extract
1079 implementation. DSA today has no driver which is MRP-aware, therefore it only
1083 - ``port_mrp_add`` and ``port_mrp_del``: notifies driver when an MRP instance
1086 - ``port_mrp_add_ring_role`` and ``port_mrp_del_ring_role``: function invoked
1091 IEC 62439-3 (HSR/PRP)
1092 ---------------------
1097 eliminating the duplicates at the receiver. The High-availability Seamless
1099 the redundant traffic are aware of the fact that it is HSR-tagged (because HSR
1109 interface with a physical switch port does not produce the expected result).
1113 ``Documentation/networking/netdev-features.rst``. Additionally, the following
1116 - ``port_hsr_join``: function invoked when a given switch port is added to a
1117   DANP/DANH. The driver may return ``-EOPNOTSUPP`` and in this case, DSA will
1120 - ``port_hsr_leave``: function invoked when a given switch port leaves a
1127 -------------------------------------------------------------
1130 capable hardware, but does not enforce a strict switch device driver model. On
1132 of the switch specific. At some point we should envision a merger between these