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
65 Switch tagging protocols
66 ------------------------
68 DSA supports many vendor-specific tagging protocols, one software-defined
69 tagging protocol, and a tag-less mode as well (``DSA_TAG_PROTO_NONE``).
74 - identifies which port the Ethernet frame came from/should be sent to
75 - provides a reason why this frame was forwarded to the management interface
82 1. The switch-specific frame header is located before the Ethernet header,
85 2. The switch-specific frame header is located before the EtherType, keeping
88 3. The switch-specific frame header is located at the tail of the packet,
92 A tagging protocol may tag all packets with switch tags of the same length, or
94 require an extended switch tag, or there might be one tag length on TX and a
97 with the length in octets of the longest switch frame header/trailer. The DSA
102 on a best-effort basis, the allocation of packets with enough extra space such
103 that the act of pushing the switch tag on transmission of a packet does not
106 Even though applications are not expected to parse DSA-specific frame headers,
111 characteristics of the interaction required between the switch hardware and the
117 switch tree use the same tagging protocol. In case of a packet transiting a
118 fabric with more than one switch, the switch-specific frame header is inserted
119 by the first switch in the fabric that the packet was received on. This header
124 other switches from the same fabric, and in this case, the outermost switch
128 by a leaf switch (not connected directly to the CPU) is not the same as what
129 the network stack sees. This can be seen with Marvell switch trees, where the
133 It still remains the case that, if the DSA switch tree is configured for the
134 EDSA tagging protocol, the operating system sees EDSA-tagged packets from the
136 because the Marvell switch connected directly to the CPU is configured to
142 no DSA links in this fabric, and each switch constitutes a disjoint DSA switch
143 tree. The DSA links are viewed as simply a pair of a DSA master (the out-facing
144 port of the upstream DSA switch) and a CPU port (the in-facing port of the
145 downstream DSA switch).
147 The tagging protocol of the attached DSA switch tree can be viewed through the
152 If the hardware and driver are capable, the tagging protocol of the DSA switch
155 all attached switch ports must be down while doing this).
161 regardless of the driver used for the switch control path, and the driver used
165 The passed ``struct sk_buff *skb`` has ``skb->data`` pointing at
169 The job of this method is to prepare the skb in a way that the switch will
177 passed ``struct sk_buff *skb`` has ``skb->data`` pointing at
180 method is to consume the frame header, adjust ``skb->data`` to really point at
181 the first octet after the EtherType, and to change ``skb->dev`` to point to the
182 virtual DSA user network interface corresponding to the physical front-facing
183 switch port that the packet was received on.
207 already expect the switch tag in use, the checksum must be calculated before any
210 when the tag gets stripped by the switch during transmission, it will leave an
214 with DSA-unaware masters, mangling what the master perceives as MAC DA), the
218 Note that this assumes a DSA-unaware master driver, which is the norm.
221 ----------------------
224 the CPU/management Ethernet interface. Such a driver might occasionally need to
230 Ethernet switch.
233 ----------------------
236 networking stack is in order to have the DSA subsystem process the Ethernet
237 switch specific tagging protocol. DSA accomplishes this by registering a
238 specific (and fake) Ethernet type (later becoming ``skb->protocol``) with the
240 Ethernet Frame receive sequence looks like this:
246         - receive function is invoked
247         - basic packet processing is done: getting length, status etc.
248         - packet is prepared to be processed by the Ethernet layer by calling
251 2. net/ethernet/eth.c::
254                   if (dev->dsa_ptr != NULL)
255                           -> skb->protocol = ETH_P_XDSA
257 3. drivers/net/ethernet/\*::
260                   -> iterate over registered packet_type
261                           -> invoke handler for ETH_P_XDSA, calls dsa_switch_rcv()
265           -> dsa_switch_rcv()
266                   -> invoke switch tag specific protocol handler in 'net/dsa/tag_*.c'
270         - inspect and strip switch tag protocol to determine originating port
271         - locate per-port network device
272         - invoke ``eth_type_trans()`` with the DSA slave network device
273         - invoked ``netif_receive_skb()``
275 Past this point, the DSA slave network devices get delivered regular Ethernet
279 ---------------------
283 controlling and data-flowing end-point for each front-panel port of the switch.
286 - insert/remove the switch tag protocol (if it exists) when sending traffic
287   to/from specific switch ports
288 - query the switch for ethtool operations: statistics, link state,
289   Wake-on-LAN, register dumps...
290 - manage external/internal PHY: link, auto-negotiation, etc.
294 stack/ethtool and the switch driver implementation.
297 switch tagging protocol is currently registered with these network devices and
299 switch tag in the Ethernet frames.
302 ``ndo_start_xmit()`` function. Since they contain the appropriate switch tag, the
303 Ethernet switch will be able to process these incoming frames from the
304 management interface and deliver them to the physical switch port.
318 towards the switch.
321 ------------------------
330            +-----------v--|--------------------+
331            |+------+ +------+ +------+ +------+|
333            |+------+-+------+-+------+-+------+|
334            |          DSA switch driver        |
335            +-----------------------------------+
338            switch driver |        | switch driver
340            +-----------------------------------+
342    --------+-----------------------------------+------------
344            +-----------------------------------+
347          switch hardware |        | switch hardware
349            +-----------------------------------+
350            |               Switch              |
351            |+------+ +------+ +------+ +------+|
353            ++------+-+------+-+------+-+------++
356 --------------
358 In order to be able to read to/from a switch PHY built into it, DSA creates a
359 slave MDIO bus which allows a specific switch driver to divert and intercept
360 MDIO reads/writes towards specific PHY addresses. In most MDIO-connected
362 to return standard MII registers from the switch builtin PHYs, allowing the PHY
363 library and/or to return link status, link partner pages, auto-negotiation
366 For Ethernet switches which have both external and internal MDIO buses, the
368 internal or external MDIO devices this switch might be connected to: internal
372 ---------------
377 - ``dsa_chip_data``: platform data configuration for a given switch device,
378   this structure describes a switch device's parent device, its address, as
382 - ``dsa_platform_data``: platform device configuration data which can reference
384   the master network device this switch tree is attached to needs to be
387 - ``dsa_switch_tree``: structure assigned to the master network device under
389   the tagging protocol supported by the switch tree, and which receive/transmit
391   switch is also provided: CPU port. Finally, a collection of dsa_switch are
394 - ``dsa_switch``: structure describing a switch device in the tree, referencing
398 - ``dsa_switch_ops``: structure referencing function pointers, see below for a
405 -------------------------------
410 - inability to fetch switch CPU port statistics counters using ethtool, which
411   can make it harder to debug MDIO switch connected using xMII interfaces
413 - inability to configure the CPU port link parameters based on the Ethernet
416 - inability to configure specific VLAN IDs / trunking VLANs between switches
420 --------------------------------
422 Once a master network device is configured to use DSA (dev->dsa_ptr becomes
423 non-NULL), and the switch behind it expects a tagging protocol, this network
426 will not make us go through the switch tagging protocol transmit function, so
427 the Ethernet switch on the other end, expecting a tag will typically drop this
435 - MDIO/PHY library: ``drivers/net/phy/phy.c``, ``mdio_bus.c``
436 - Switchdev:``net/switchdev/*``
437 - Device Tree for various of_* functions
438 - Devlink: ``net/core/devlink.c``
441 ----------------
447 - internal PHY devices, built into the Ethernet switch hardware
448 - external PHY devices, connected via an internal or external MDIO bus
449 - internal PHY devices, connected via an internal MDIO bus
450 - special, non-autonegotiated or non MDIO-managed PHY devices: SFPs, MoCA; a.k.a
456 - if Device Tree is used, the PHY device is looked up using the standard
457   "phy-handle" property, if found, this PHY device is created and registered
460 - if Device Tree is used and the PHY device is "fixed", that is, conforms to
461   the definition of a non-MDIO managed PHY as defined in
462   ``Documentation/devicetree/bindings/net/fixed-link.txt``, the PHY is registered
465 - finally, if the PHY is built into the switch, as is very common with
466   standalone switch packages, the PHY is probed using the slave MII bus created
471 ---------
475 of per-port slave network devices. As of today, the only SWITCHDEV objects
479 -------
481 DSA registers one devlink device per physical switch in the fabric.
487 - Regions: debugging feature which allows user space to dump driver-defined
488   areas of hardware information in a low-level, binary format. Both global
489   regions as well as per-port regions are supported. It is possible to export
491   to the standard iproute2 user space programs (ip-link, bridge), like address
493   contain additional hardware-specific details which are not visible through
495   the non-user ports too, which are invisible to iproute2 because no network
497 - Params: a feature which enables user to configure certain low-level tunable
499   devlink params, or may add new device-specific devlink params.
500 - Resources: a monitoring feature which enables users to see the degree of
502 - Shared buffers: a QoS feature for adjusting and partitioning memory and frame
504   directions, such that low-priority bulk traffic does not impede the
505   processing of high-priority critical traffic.
510 -----------
515 per-port PHY specific details: interface connection, MDIO bus location, etc.
520 DSA switch drivers need to implement a ``dsa_switch_ops`` structure which will
524 -----------------------------------------
530 Switch registration from the perspective of a driver means passing a valid
532 switch driver's probing function. The following members must be valid in the
535 - ``ds->dev``: will be used to parse the switch's OF node or platform data.
537 - ``ds->num_ports``: will be used to create the port list for this switch, and
540 - ``ds->ops``: a pointer to the ``dsa_switch_ops`` structure holding the DSA
543 - ``ds->priv``: backpointer to a driver-private data structure which can be
547 be configured to obtain driver-specific behavior from the DSA core. Their
550 - ``ds->vlan_filtering_is_global``
552 - ``ds->needs_standalone_vlan_filtering``
554 - ``ds->configure_vlan_while_not_filtering``
556 - ``ds->untag_bridge_pvid``
558 - ``ds->assisted_learning_on_cpu_port``
560 - ``ds->mtu_enforcement_ingress``
562 - ``ds->fdb_isolation``
564 Internally, DSA keeps an array of switch trees (group of switches) global to
566 The tree ID to which the switch is attached is determined by the first u32
567 number of the ``dsa,member`` property of the switch's OF node (0 if missing).
568 The switch ID within the tree is determined by the second u32 number of the
570 switch ID and tree ID is illegal and will cause an error. Using platform data,
571 a single switch and a single switch tree is permitted.
574 The first N-1 callers of ``dsa_register_switch()`` only add their ports to the
575 port list of the tree (``dst->ports``), each port having a backpointer to its
576 associated switch (``dp->ds``). Then, these switches exit their
580 the last switch calls ``dsa_register_switch()``, and this triggers the effective
581 continuation of initialization (including the call to ``ds->ops->setup()``) for
583 switch's probe function.
586 which removes a switch's ports from the port list of the tree. The entire tree
587 is torn down when the first switch unregisters.
589 It is mandatory for DSA switch drivers to implement the ``shutdown()`` callback
607 Switch configuration
608 --------------------
610 - ``get_tag_protocol``: this is to indicate what kind of tagging protocol is
614   upstream switch, in case there are hardware limitations in terms of supported
617 - ``change_tag_protocol``: when the default tagging protocol has compatibility
623 - ``setup``: setup function for the switch, this function is responsible for setting
626   configure the switch to separate all network interfaces from each other, that
627   is, they should be isolated by the switch hardware itself, typically by creating
628   a Port-based VLAN ID for each port and allowing only the CPU port and the
630   platform should be disabled. Past this function, the switch is expected to be
632   to issue a software reset of the switch during this setup function in order to
637 - ``port_setup`` and ``port_teardown``: methods for initialization and
638   destruction of per-port data structures. It is mandatory for some operations
643   PHY cannot be found. In this case, probing of the DSA switch continues
646 - ``port_change_master``: method through which the affinity (association used
655   master->dsa_ptr``. Additionally, the master can also be a LAG device where
657   valid ``master->dsa_ptr`` pointer, however this is not unique, but rather a
665 -------------------------------
667 - ``get_phy_flags``: Some switches are interfaced to various kinds of Ethernet PHYs,
669   on its own (e.g.: coming from switch memory mapped registers), this function
670   should return a 32-bit bitmask of "flags" that is private between the switch
671   driver and the Ethernet PHY driver in ``drivers/net/phy/\*``.
673 - ``phy_read``: Function invoked by the DSA slave MDIO bus when attempting to read
674   the switch port MDIO registers. If unavailable, return 0xffff for each read.
675   For builtin switch Ethernet PHYs, this function should allow reading the link
676   status, auto-negotiation results, link partner pages, etc.
678 - ``phy_write``: Function invoked by the DSA slave MDIO bus when attempting to write
679   to the switch port MDIO registers. If unavailable return a negative error
682 - ``adjust_link``: Function invoked by the PHY library when a slave network device
684   configuring the switch port link parameters: speed, duplex, pause based on
687 - ``fixed_link_update``: Function invoked by the PHY library, and specifically by
688   the fixed PHY driver asking the switch driver for link parameters that could
689   not be auto-negotiated, or obtained by reading the PHY registers through MDIO.
691   MoCA or other kinds of non-MDIO managed PHYs where out of band link
695 ------------------
697 - ``get_strings``: ethtool function used to query the driver's strings, will
700 - ``get_ethtool_stats``: ethtool function used to query per-port statistics and
702   RX/TX counters from the network device, with switch driver specific statistics
705 - ``get_sset_count``: ethtool function used to query the number of statistics items
707 - ``get_wol``: ethtool function used to obtain Wake-on-LAN settings per-port, this
709   Wake-on-LAN settings if this interface needs to participate in Wake-on-LAN
711 - ``set_wol``: ethtool function used to configure Wake-on-LAN settings per-port,
714 - ``set_eee``: ethtool function which is used to configure a switch port EEE (Green
715   Ethernet) settings, can optionally invoke the PHY library to enable EEE at the
716   PHY level if relevant. This function should enable EEE at the switch port MAC
717   controller and data-processing logic
719 - ``get_eee``: ethtool function which is used to query a switch port EEE settings,
720   this function should return the EEE state of the switch port MAC controller
721   and data-processing logic as well as query the PHY for its currently configured
724 - ``get_eeprom_len``: ethtool function returning for a given switch the EEPROM
727 - ``get_eeprom``: ethtool function returning for a given switch the EEPROM contents
729 - ``set_eeprom``: ethtool function writing specified data to a given switch EEPROM
731 - ``get_regs_len``: ethtool function returning the register length for a given
732   switch
734 - ``get_regs``: ethtool function returning the Ethernet switch internal register
735   contents. This function might require user-land code in ethtool to
736   pretty-print register values and registers
739 ----------------
741 - ``suspend``: function invoked by the DSA platform device when the system goes to
742   suspend, should quiesce all Ethernet switch activities, but keep ports
743   participating in Wake-on-LAN active as well as additional wake-up logic if
746 - ``resume``: function invoked by the DSA platform device when the system resumes,
747   should resume all Ethernet switch activities and re-configure the switch to be
750 - ``port_enable``: function invoked by the DSA slave network device ndo_open
752   fully enable a given switch port. DSA takes care of marking the port with
756 - ``port_disable``: function invoked by the DSA slave network device ndo_close
758   fully disable a given switch port. DSA takes care of marking the port with
763 -----------------
772 For example, all ports that belong to a VLAN-unaware bridge (which is
773 *currently* VLAN-unaware) are expected to learn source addresses in the
775 VLAN-unaware bridges). During forwarding and FDB lookup, a packet received on a
776 VLAN-unaware bridge port should be able to find a VLAN-unaware FDB entry having
780 a port which is a member of a different VLAN-unaware bridge (and is therefore
783 Similarly, each VLAN of each offloaded VLAN-aware bridge should have an
788 In this context, a VLAN-unaware database means that all packets are expected to
790 VLAN-aware database means that packets are supposed to match based on the VLAN
793 At the bridge layer, VLAN-unaware FDB entries have the special VID value of 0,
794 whereas VLAN-aware FDB entries have non-zero VID values. Note that a
795 VLAN-unaware bridge may have VLAN-aware (non-zero VID) FDB entries, and a
796 VLAN-aware bridge may have VLAN-unaware FDB entries. As in hardware, the
818 Switch drivers which satisfy certain criteria are able to optimize the naive
819 configuration by removing the CPU port from the flooding domain of the switch,
828 - Primary unicast MAC addresses of ports (``dev->dev_addr``). These are
833 - Secondary unicast and multicast MAC addresses of ports (addresses added
837 - Local/permanent bridge FDB entries (``BR_FDB_LOCAL``). These are the MAC
842 - Static bridge FDB entries installed towards foreign (non-DSA) interfaces
843   present in the same bridge as some DSA switch ports. These are also
846 - Dynamically learned FDB entries on foreign interfaces present in the same
847   bridge as some DSA switch ports, only if ``ds->assisted_learning_on_cpu_port``
854 - ``DSA_DB_PORT``: the FDB (or MDB) entry to be installed or deleted belongs to
855   the port private database of user port ``db->dp``.
856 - ``DSA_DB_BRIDGE``: the entry belongs to one of the address databases of bridge
857   ``db->bridge``. Separation between the VLAN-unaware database and the per-VID
859 - ``DSA_DB_LAG``: the entry belongs to the address database of LAG ``db->lag``.
863 ``port_mdb_add`` etc should declare ``ds->fdb_isolation`` as true.
865 DSA associates each offloaded bridge and each offloaded LAG with a one-based ID
868 scheme (the ID is readable through ``db->bridge.num`` and ``db->lag.id`` or may
874 drivers even if they do not support FDB isolation. However, ``db->bridge.num``
875 and ``db->lag.id`` are always set to 0 in that case (to denote the lack of
878 Note that it is not mandatory for a switch driver to implement physically
882 share the same database, but the reference counting of host-filtered addresses
893 ------------
896 below. They may be absent, return -EOPNOTSUPP, or ``ds->max_num_bridges`` may
897 be non-zero and exceeded, and in this case, joining a bridge port is still
911 ingress switch port. DSA, through ``dsa_port_devlink_setup()``, considers all
912 switch ports part of the same tree ID to be part of the same bridge forwarding
922 packets and have ``skb->offload_fwd_mark`` set to true in the tag protocol
932 VLAN-unaware, and in this case the FID must be equal to the FID used by the
933 driver for its VLAN-unaware address database associated with that bridge.
934 Alternatively, the bridge may be VLAN-aware, and in that case, it is guaranteed
935 that the packet is also VLAN-tagged with the VLAN ID that the bridge processed
937 the egress-untagged ports, or keep the tag on the egress-tagged ones.
939 - ``port_bridge_join``: bridge layer function invoked when a given switch port is
940   added to a bridge, this function should do what's necessary at the switch
946 - ``port_bridge_leave``: bridge layer function invoked when a given switch port is
948   switch level to deny the leaving port from ingress/egress traffic from the
951 - ``port_stp_state_set``: bridge layer function invoked when a given switch port STP
952   state is computed by the bridge layer and should be propagated to switch
955 - ``port_bridge_flags``: bridge layer function invoked when a port must
957   learning. The switch driver is responsible for initial setup of the
966 - ``port_fast_age``: bridge layer function invoked when flushing the
973 ---------------------
975 - ``port_vlan_filtering``: bridge layer function invoked when the bridge gets
980   VLAN ID map/rules.  If there is no PVID programmed into the switch port,
981   untagged frames must be rejected as well. When turned off the switch must
985 - ``port_vlan_add``: bridge layer function invoked when a VLAN is configured
986   (tagged or untagged) for the given switch port. The CPU port becomes a member
994 - ``port_vlan_del``: bridge layer function invoked when a VLAN is removed from the
995   given switch port
997 - ``port_fdb_add``: bridge layer function invoked when the bridge wants to install a
998   Forwarding Database entry, the switch hardware should be programmed with the
1002 - ``port_fdb_del``: bridge layer function invoked when the bridge wants to remove a
1003   Forwarding Database entry, the switch hardware should be programmed to delete
1007 - ``port_fdb_dump``: bridge bypass function invoked by ``ndo_fdb_dump`` on the
1014 - ``port_mdb_add``: bridge layer function invoked when the bridge wants to install
1015   a multicast database entry. The switch hardware should be programmed with the
1019 - ``port_mdb_del``: bridge layer function invoked when the bridge wants to remove a
1020   multicast database entry, the switch hardware should be programmed to delete
1025 ----------------
1042 - ``port_lag_join``: function invoked when a given switch port is added to a
1043   LAG. The driver may return ``-EOPNOTSUPP``, and in this case, DSA will fall
1046 - ``port_lag_leave``: function invoked when a given switch port leaves a LAG
1048 - ``port_lag_change``: function invoked when the link state of any member of
1053 can optionally populate ``ds->num_lag_ids`` from the ``dsa_switch_ops::setup``
1055 retrieved by a DSA switch driver using the ``dsa_lag_id`` function.
1057 IEC 62439-2 (MRP)
1058 -----------------
1073 necessary for the hardware, even if it is not MRP-aware, to be able to extract
1075 implementation. DSA today has no driver which is MRP-aware, therefore it only
1079 - ``port_mrp_add`` and ``port_mrp_del``: notifies driver when an MRP instance
1082 - ``port_mrp_add_ring_role`` and ``port_mrp_del_ring_role``: function invoked
1087 IEC 62439-3 (HSR/PRP)
1088 ---------------------
1093 eliminating the duplicates at the receiver. The High-availability Seamless
1095 the redundant traffic are aware of the fact that it is HSR-tagged (because HSR
1105 interface with a physical switch port does not produce the expected result).
1109 ``Documentation/networking/netdev-features.rst``. Additionally, the following
1112 - ``port_hsr_join``: function invoked when a given switch port is added to a
1113   DANP/DANH. The driver may return ``-EOPNOTSUPP`` and in this case, DSA will
1116 - ``port_hsr_leave``: function invoked when a given switch port leaves a
1123 -------------------------------------------------------------
1126 capable hardware, but does not enforce a strict switch device driver model. On
1128 of the switch specific. At some point we should envision a merger between these