1============ 2Architecture 3============ 4 5This document describes the **Distributed Switch Architecture (DSA)** subsystem 6design principles, limitations, interactions with other subsystems, and how to 7develop drivers for this subsystem as well as a TODO for developers interested 8in joining the effort. 9 10Design principles 11================= 12 13The Distributed Switch Architecture subsystem was primarily designed to 14support Marvell Ethernet switches (MV88E6xxx, a.k.a. Link Street product 15line) using Linux, but has since evolved to support other vendors as well. 16 17The original philosophy behind this design was to be able to use unmodified 18Linux tools such as bridge, iproute2, ifconfig to work transparently whether 19they configured/queried a switch port network device or a regular network 20device. 21 22An Ethernet switch typically comprises multiple front-panel ports and one 23or more CPU or management ports. The DSA subsystem currently relies on the 24presence of a management port connected to an Ethernet controller capable of 25receiving Ethernet frames from the switch. This is a very common setup for all 26kinds of Ethernet switches found in Small Home and Office products: routers, 27gateways, or even top-of-rack switches. This host Ethernet controller will 28be later referred to as "conduit" and "cpu" in DSA terminology and code. 29 30The D in DSA stands for Distributed, because the subsystem has been designed 31with the ability to configure and manage cascaded switches on top of each other 32using upstream and downstream Ethernet links between switches. These specific 33ports are referred to as "dsa" ports in DSA terminology and code. A collection 34of multiple switches connected to each other is called a "switch tree". 35 36For each front-panel port, DSA creates specialized network devices which are 37used as controlling and data-flowing endpoints for use by the Linux networking 38stack. These specialized network interfaces are referred to as "user" network 39interfaces in DSA terminology and code. 40 41The ideal case for using DSA is when an Ethernet switch supports a "switch tag" 42which is a hardware feature making the switch insert a specific tag for each 43Ethernet frame it receives to/from specific ports to help the management 44interface figure out: 45 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 49 50The subsystem does support switches not capable of inserting/stripping tags, but 51the features might be slightly limited in that case (traffic separation relies 52on Port-based VLAN IDs). 53 54Note that DSA does not currently create network interfaces for the "cpu" and 55"dsa" ports because: 56 57- the "cpu" port is the Ethernet switch facing side of the management 58 controller, and as such, would create a duplication of feature, since you 59 would get two interfaces for the same conduit: conduit netdev, and "cpu" netdev 60 61- the "dsa" port(s) are just conduits between two or more switches, and as such 62 cannot really be used as proper network interfaces either, only the 63 downstream, or the top-most upstream interface makes sense with that model 64 65NB: for the past 15 years, the DSA subsystem had been making use of the terms 66"master" (rather than "conduit") and "slave" (rather than "user"). These terms 67have been removed from the DSA codebase and phased out of the uAPI. 68 69Switch tagging protocols 70------------------------ 71 72DSA supports many vendor-specific tagging protocols, one software-defined 73tagging protocol, and a tag-less mode as well (``DSA_TAG_PROTO_NONE``). 74 75The exact format of the tag protocol is vendor specific, but in general, they 76all contain something which: 77 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 80 81All tagging protocols are in ``net/dsa/tag_*.c`` files and implement the 82methods of the ``struct dsa_device_ops`` structure, which are detailed below. 83 84Tagging protocols generally fall in one of three categories: 85 861. The switch-specific frame header is located before the Ethernet header, 87 shifting to the right (from the perspective of the DSA conduit's frame 88 parser) the MAC DA, MAC SA, EtherType and the entire L2 payload. 892. The switch-specific frame header is located before the EtherType, keeping 90 the MAC DA and MAC SA in place from the DSA conduit's perspective, but 91 shifting the 'real' EtherType and L2 payload to the right. 923. The switch-specific frame header is located at the tail of the packet, 93 keeping all frame headers in place and not altering the view of the packet 94 that the DSA conduit's frame parser has. 95 96A tagging protocol may tag all packets with switch tags of the same length, or 97the tag length might vary (for example packets with PTP timestamps might 98require an extended switch tag, or there might be one tag length on TX and a 99different one on RX). Either way, the tagging protocol driver must populate the 100``struct dsa_device_ops::needed_headroom`` and/or ``struct dsa_device_ops::needed_tailroom`` 101with the length in octets of the longest switch frame header/trailer. The DSA 102framework will automatically adjust the MTU of the conduit interface to 103accommodate for this extra size in order for DSA user ports to support the 104standard MTU (L2 payload length) of 1500 octets. The ``needed_headroom`` and 105``needed_tailroom`` properties are also used to request from the network stack, 106on a best-effort basis, the allocation of packets with enough extra space such 107that the act of pushing the switch tag on transmission of a packet does not 108cause it to reallocate due to lack of memory. 109 110Even though applications are not expected to parse DSA-specific frame headers, 111the format on the wire of the tagging protocol represents an Application Binary 112Interface exposed by the kernel towards user space, for decoders such as 113``libpcap``. The tagging protocol driver must populate the ``proto`` member of 114``struct dsa_device_ops`` with a value that uniquely describes the 115characteristics of the interaction required between the switch hardware and the 116data path driver: the offset of each bit field within the frame header and any 117stateful processing required to deal with the frames (as may be required for 118PTP timestamping). 119 120From the perspective of the network stack, all switches within the same DSA 121switch tree use the same tagging protocol. In case of a packet transiting a 122fabric with more than one switch, the switch-specific frame header is inserted 123by the first switch in the fabric that the packet was received on. This header 124typically contains information regarding its type (whether it is a control 125frame that must be trapped to the CPU, or a data frame to be forwarded). 126Control frames should be decapsulated only by the software data path, whereas 127data frames might also be autonomously forwarded towards other user ports of 128other switches from the same fabric, and in this case, the outermost switch 129ports must decapsulate the packet. 130 131Note that in certain cases, it might be the case that the tagging format used 132by a leaf switch (not connected directly to the CPU) is not the same as what 133the network stack sees. This can be seen with Marvell switch trees, where the 134CPU port can be configured to use either the DSA or the Ethertype DSA (EDSA) 135format, but the DSA links are configured to use the shorter (without Ethertype) 136DSA frame header, in order to reduce the autonomous packet forwarding overhead. 137It still remains the case that, if the DSA switch tree is configured for the 138EDSA tagging protocol, the operating system sees EDSA-tagged packets from the 139leaf switches that tagged them with the shorter DSA header. This can be done 140because the Marvell switch connected directly to the CPU is configured to 141perform tag translation between DSA and EDSA (which is simply the operation of 142adding or removing the ``ETH_P_EDSA`` EtherType and some padding octets). 143 144It is possible to construct cascaded setups of DSA switches even if their 145tagging protocols are not compatible with one another. In this case, there are 146no DSA links in this fabric, and each switch constitutes a disjoint DSA switch 147tree. The DSA links are viewed as simply a pair of a DSA conduit (the out-facing 148port of the upstream DSA switch) and a CPU port (the in-facing port of the 149downstream DSA switch). 150 151The tagging protocol of the attached DSA switch tree can be viewed through the 152``dsa/tagging`` sysfs attribute of the DSA conduit:: 153 154 cat /sys/class/net/eth0/dsa/tagging 155 156If the hardware and driver are capable, the tagging protocol of the DSA switch 157tree can be changed at runtime. This is done by writing the new tagging 158protocol name to the same sysfs device attribute as above (the DSA conduit and 159all attached switch ports must be down while doing this). 160 161It is desirable that all tagging protocols are testable with the ``dsa_loop`` 162mockup driver, which can be attached to any network interface. The goal is that 163any network interface should be capable of transmitting the same packet in the 164same way, and the tagger should decode the same received packet in the same way 165regardless of the driver used for the switch control path, and the driver used 166for the DSA conduit. 167 168The transmission of a packet goes through the tagger's ``xmit`` function. 169The passed ``struct sk_buff *skb`` has ``skb->data`` pointing at 170``skb_mac_header(skb)``, i.e. at the destination MAC address, and the passed 171``struct net_device *dev`` represents the virtual DSA user network interface 172whose hardware counterpart the packet must be steered to (i.e. ``swp0``). 173The job of this method is to prepare the skb in a way that the switch will 174understand what egress port the packet is for (and not deliver it towards other 175ports). Typically this is fulfilled by pushing a frame header. Checking for 176insufficient size in the skb headroom or tailroom is unnecessary provided that 177the ``needed_headroom`` and ``needed_tailroom`` properties were filled out 178properly, because DSA ensures there is enough space before calling this method. 179 180The reception of a packet goes through the tagger's ``rcv`` function. The 181passed ``struct sk_buff *skb`` has ``skb->data`` pointing at 182``skb_mac_header(skb) + ETH_ALEN`` octets, i.e. to where the first octet after 183the EtherType would have been, were this frame not tagged. The role of this 184method is to consume the frame header, adjust ``skb->data`` to really point at 185the first octet after the EtherType, and to change ``skb->dev`` to point to the 186virtual DSA user network interface corresponding to the physical front-facing 187switch port that the packet was received on. 188 189Since tagging protocols in category 1 and 2 break software (and most often also 190hardware) packet dissection on the DSA conduit, features such as RPS (Receive 191Packet Steering) on the DSA conduit would be broken. The DSA framework deals 192with this by hooking into the flow dissector and shifting the offset at which 193the IP header is to be found in the tagged frame as seen by the DSA conduit. 194This behavior is automatic based on the ``overhead`` value of the tagging 195protocol. If not all packets are of equal size, the tagger can implement the 196``flow_dissect`` method of the ``struct dsa_device_ops`` and override this 197default behavior by specifying the correct offset incurred by each individual 198RX packet. Tail taggers do not cause issues to the flow dissector. 199 200Checksum offload should work with category 1 and 2 taggers when the DSA conduit 201driver declares NETIF_F_HW_CSUM in vlan_features and looks at csum_start and 202csum_offset. For those cases, DSA will shift the checksum start and offset by 203the tag size. If the DSA conduit driver still uses the legacy NETIF_F_IP_CSUM 204or NETIF_F_IPV6_CSUM in vlan_features, the offload might only work if the 205offload hardware already expects that specific tag (perhaps due to matching 206vendors). DSA user ports inherit those flags from the conduit, and it is up to 207the driver to correctly fall back to software checksum when the IP header is not 208where the hardware expects. If that check is ineffective, the packets might go 209to the network without a proper checksum (the checksum field will have the 210pseudo IP header sum). For category 3, when the offload hardware does not 211already expect the switch tag in use, the checksum must be calculated before any 212tag is inserted (i.e. inside the tagger). Otherwise, the DSA conduit would 213include the tail tag in the (software or hardware) checksum calculation. Then, 214when the tag gets stripped by the switch during transmission, it will leave an 215incorrect IP checksum in place. 216 217Due to various reasons (most common being category 1 taggers being associated 218with DSA-unaware conduits, mangling what the conduit perceives as MAC DA), the 219tagging protocol may require the DSA conduit to operate in promiscuous mode, to 220receive all frames regardless of the value of the MAC DA. This can be done by 221setting the ``promisc_on_conduit`` property of the ``struct dsa_device_ops``. 222Note that this assumes a DSA-unaware conduit driver, which is the norm. 223 224Conduit network devices 225----------------------- 226 227Conduit network devices are regular, unmodified Linux network device drivers for 228the CPU/management Ethernet interface. Such a driver might occasionally need to 229know whether DSA is enabled (e.g.: to enable/disable specific offload features), 230but the DSA subsystem has been proven to work with industry standard drivers: 231``e1000e,`` ``mv643xx_eth`` etc. without having to introduce modifications to these 232drivers. Such network devices are also often referred to as conduit network 233devices since they act as a pipe between the host processor and the hardware 234Ethernet switch. 235 236Networking stack hooks 237---------------------- 238 239When a conduit netdev is used with DSA, a small hook is placed in the 240networking stack is in order to have the DSA subsystem process the Ethernet 241switch specific tagging protocol. DSA accomplishes this by registering a 242specific (and fake) Ethernet type (later becoming ``skb->protocol``) with the 243networking stack, this is also known as a ``ptype`` or ``packet_type``. A typical 244Ethernet Frame receive sequence looks like this: 245 246Conduit network device (e.g.: e1000e): 247 2481. Receive interrupt fires: 249 250 - 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 253 ``eth_type_trans`` 254 2552. net/ethernet/eth.c:: 256 257 eth_type_trans(skb, dev) 258 if (dev->dsa_ptr != NULL) 259 -> skb->protocol = ETH_P_XDSA 260 2613. drivers/net/ethernet/\*:: 262 263 netif_receive_skb(skb) 264 -> iterate over registered packet_type 265 -> invoke handler for ETH_P_XDSA, calls dsa_switch_rcv() 266 2674. net/dsa/dsa.c:: 268 269 -> dsa_switch_rcv() 270 -> invoke switch tag specific protocol handler in 'net/dsa/tag_*.c' 271 2725. net/dsa/tag_*.c: 273 274 - 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()`` 278 279Past this point, the DSA user network devices get delivered regular Ethernet 280frames that can be processed by the networking stack. 281 282User network devices 283-------------------- 284 285User network devices created by DSA are stacked on top of their conduit network 286device, each of these network interfaces will be responsible for being a 287controlling and data-flowing end-point for each front-panel port of the switch. 288These interfaces are specialized in order to: 289 290- 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. 295 296These user network devices have custom net_device_ops and ethtool_ops function 297pointers which allow DSA to introduce a level of layering between the networking 298stack/ethtool and the switch driver implementation. 299 300Upon frame transmission from these user network devices, DSA will look up which 301switch tagging protocol is currently registered with these network devices and 302invoke a specific transmit routine which takes care of adding the relevant 303switch tag in the Ethernet frames. 304 305These frames are then queued for transmission using the conduit network device 306``ndo_start_xmit()`` function. Since they contain the appropriate switch tag, the 307Ethernet switch will be able to process these incoming frames from the 308management interface and deliver them to the physical switch port. 309 310When using multiple CPU ports, it is possible to stack a LAG (bonding/team) 311device between the DSA user devices and the physical DSA conduits. The LAG 312device is thus also a DSA conduit, but the LAG slave devices continue to be DSA 313conduits as well (just with no user port assigned to them; this is needed for 314recovery in case the LAG DSA conduit disappears). Thus, the data path of the LAG 315DSA conduit is used asymmetrically. On RX, the ``ETH_P_XDSA`` handler, which 316calls ``dsa_switch_rcv()``, is invoked early (on the physical DSA conduit; 317LAG slave). Therefore, the RX data path of the LAG DSA conduit is not used. 318On the other hand, TX takes place linearly: ``dsa_user_xmit`` calls 319``dsa_enqueue_skb``, which calls ``dev_queue_xmit`` towards the LAG DSA conduit. 320The latter calls ``dev_queue_xmit`` towards one physical DSA conduit or the 321other, and in both cases, the packet exits the system through a hardware path 322towards the switch. 323 324Graphical representation 325------------------------ 326 327Summarized, this is basically how DSA looks like from a network device 328perspective:: 329 330 Unaware application 331 opens and binds socket 332 | ^ 333 | | 334 +-----------v--|--------------------+ 335 |+------+ +------+ +------+ +------+| 336 || swp0 | | swp1 | | swp2 | | swp3 || 337 |+------+-+------+-+------+-+------+| 338 | DSA switch driver | 339 +-----------------------------------+ 340 | ^ 341 Tag added by | | Tag consumed by 342 switch driver | | switch driver 343 v | 344 +-----------------------------------+ 345 | Unmodified host interface driver | Software 346 --------+-----------------------------------+------------ 347 | Host interface (eth0) | Hardware 348 +-----------------------------------+ 349 | ^ 350 Tag consumed by | | Tag added by 351 switch hardware | | switch hardware 352 v | 353 +-----------------------------------+ 354 | Switch | 355 |+------+ +------+ +------+ +------+| 356 || swp0 | | swp1 | | swp2 | | swp3 || 357 ++------+-+------+-+------+-+------++ 358 359User MDIO bus 360------------- 361 362In order to be able to read to/from a switch PHY built into it, DSA creates an 363user MDIO bus which allows a specific switch driver to divert and intercept 364MDIO reads/writes towards specific PHY addresses. In most MDIO-connected 365switches, these functions would utilize direct or indirect PHY addressing mode 366to return standard MII registers from the switch builtin PHYs, allowing the PHY 367library and/or to return link status, link partner pages, auto-negotiation 368results, etc. 369 370For Ethernet switches which have both external and internal MDIO buses, the 371user MII bus can be utilized to mux/demux MDIO reads and writes towards either 372internal or external MDIO devices this switch might be connected to: internal 373PHYs, external PHYs, or even external switches. 374 375Data structures 376--------------- 377 378DSA data structures are defined in ``include/net/dsa.h`` as well as 379``net/dsa/dsa_priv.h``: 380 381- ``dsa_chip_data``: platform data configuration for a given switch device, 382 this structure describes a switch device's parent device, its address, as 383 well as various properties of its ports: names/labels, and finally a routing 384 table indication (when cascading switches) 385 386- ``dsa_switch_tree``: structure assigned to the conduit network device under 387 ``dsa_ptr``, this structure references a dsa_platform_data structure as well as 388 the tagging protocol supported by the switch tree, and which receive/transmit 389 function hooks should be invoked, information about the directly attached 390 switch is also provided: CPU port. Finally, a collection of dsa_switch are 391 referenced to address individual switches in the tree. 392 393- ``dsa_switch``: structure describing a switch device in the tree, referencing 394 a ``dsa_switch_tree`` as a backpointer, user network devices, conduit network 395 device, and a reference to the backing``dsa_switch_ops`` 396 397- ``dsa_switch_ops``: structure referencing function pointers, see below for a 398 full description. 399 400Design limitations 401================== 402 403Lack of CPU/DSA network devices 404------------------------------- 405 406DSA does not currently create user network devices for the CPU or DSA ports, as 407described before. This might be an issue in the following cases: 408 409- inability to fetch switch CPU port statistics counters using ethtool, which 410 can make it harder to debug MDIO switch connected using xMII interfaces 411 412- inability to configure the CPU port link parameters based on the Ethernet 413 controller capabilities attached to it: http://patchwork.ozlabs.org/patch/509806/ 414 415- inability to configure specific VLAN IDs / trunking VLANs between switches 416 when using a cascaded setup 417 418Common pitfalls using DSA setups 419-------------------------------- 420 421Once a conduit network device is configured to use DSA (dev->dsa_ptr becomes 422non-NULL), and the switch behind it expects a tagging protocol, this network 423interface can only exclusively be used as a conduit interface. Sending packets 424directly through this interface (e.g.: opening a socket using this interface) 425will not make us go through the switch tagging protocol transmit function, so 426the Ethernet switch on the other end, expecting a tag will typically drop this 427frame. 428 429Interactions with other subsystems 430================================== 431 432DSA currently leverages the following subsystems: 433 434- MDIO/PHY library: ``drivers/net/phy/phy.c``, ``mdio_bus.c`` 435- Switchdev:``net/switchdev/*`` 436- Device Tree for various of_* functions 437- Devlink: ``net/core/devlink.c`` 438 439MDIO/PHY library 440---------------- 441 442User network devices exposed by DSA may or may not be interfacing with PHY 443devices (``struct phy_device`` as defined in ``include/linux/phy.h)``, but the DSA 444subsystem deals with all possible combinations: 445 446- internal PHY devices, built into the Ethernet switch hardware 447- external PHY devices, connected via an internal or external MDIO bus 448- internal PHY devices, connected via an internal MDIO bus 449- special, non-autonegotiated or non MDIO-managed PHY devices: SFPs, MoCA; a.k.a 450 fixed PHYs 451 452The PHY configuration is done by the ``dsa_user_phy_setup()`` function and the 453logic basically looks like this: 454 455- if Device Tree is used, the PHY device is looked up using the standard 456 "phy-handle" property, if found, this PHY device is created and registered 457 using ``of_phy_connect()`` 458 459- if Device Tree is used and the PHY device is "fixed", that is, conforms to 460 the definition of a non-MDIO managed PHY as defined in 461 ``Documentation/devicetree/bindings/net/fixed-link.txt``, the PHY is registered 462 and connected transparently using the special fixed MDIO bus driver 463 464- finally, if the PHY is built into the switch, as is very common with 465 standalone switch packages, the PHY is probed using the user MII bus created 466 by DSA 467 468 469SWITCHDEV 470--------- 471 472DSA directly utilizes SWITCHDEV when interfacing with the bridge layer, and 473more specifically with its VLAN filtering portion when configuring VLANs on top 474of per-port user network devices. As of today, the only SWITCHDEV objects 475supported by DSA are the FDB and VLAN objects. 476 477Devlink 478------- 479 480DSA registers one devlink device per physical switch in the fabric. 481For each devlink device, every physical port (i.e. user ports, CPU ports, DSA 482links or unused ports) is exposed as a devlink port. 483 484DSA drivers can make use of the following devlink features: 485 486- Regions: debugging feature which allows user space to dump driver-defined 487 areas of hardware information in a low-level, binary format. Both global 488 regions as well as per-port regions are supported. It is possible to export 489 devlink regions even for pieces of data that are already exposed in some way 490 to the standard iproute2 user space programs (ip-link, bridge), like address 491 tables and VLAN tables. For example, this might be useful if the tables 492 contain additional hardware-specific details which are not visible through 493 the iproute2 abstraction, or it might be useful to inspect these tables on 494 the non-user ports too, which are invisible to iproute2 because no network 495 interface is registered for them. 496- Params: a feature which enables user to configure certain low-level tunable 497 knobs pertaining to the device. Drivers may implement applicable generic 498 devlink params, or may add new device-specific devlink params. 499- Resources: a monitoring feature which enables users to see the degree of 500 utilization of certain hardware tables in the device, such as FDB, VLAN, etc. 501- Shared buffers: a QoS feature for adjusting and partitioning memory and frame 502 reservations per port and per traffic class, in the ingress and egress 503 directions, such that low-priority bulk traffic does not impede the 504 processing of high-priority critical traffic. 505 506For more details, consult ``Documentation/networking/devlink/``. 507 508Device Tree 509----------- 510 511DSA features a standardized binding which is documented in 512``Documentation/devicetree/bindings/net/dsa/dsa.txt``. PHY/MDIO library helper 513functions such as ``of_get_phy_mode()``, ``of_phy_connect()`` are also used to query 514per-port PHY specific details: interface connection, MDIO bus location, etc. 515 516Driver development 517================== 518 519DSA switch drivers need to implement a ``dsa_switch_ops`` structure which will 520contain the various members described below. 521 522Probing, registration and device lifetime 523----------------------------------------- 524 525DSA switches are regular ``device`` structures on buses (be they platform, SPI, 526I2C, MDIO or otherwise). The DSA framework is not involved in their probing 527with the device core. 528 529Switch registration from the perspective of a driver means passing a valid 530``struct dsa_switch`` pointer to ``dsa_register_switch()``, usually from the 531switch driver's probing function. The following members must be valid in the 532provided structure: 533 534- ``ds->dev``: will be used to parse the switch's OF node or platform data. 535 536- ``ds->num_ports``: will be used to create the port list for this switch, and 537 to validate the port indices provided in the OF node. 538 539- ``ds->ops``: a pointer to the ``dsa_switch_ops`` structure holding the DSA 540 method implementations. 541 542- ``ds->priv``: backpointer to a driver-private data structure which can be 543 retrieved in all further DSA method callbacks. 544 545In addition, the following flags in the ``dsa_switch`` structure may optionally 546be configured to obtain driver-specific behavior from the DSA core. Their 547behavior when set is documented through comments in ``include/net/dsa.h``. 548 549- ``ds->vlan_filtering_is_global`` 550 551- ``ds->needs_standalone_vlan_filtering`` 552 553- ``ds->configure_vlan_while_not_filtering`` 554 555- ``ds->untag_bridge_pvid`` 556 557- ``ds->assisted_learning_on_cpu_port`` 558 559- ``ds->mtu_enforcement_ingress`` 560 561- ``ds->fdb_isolation`` 562 563Internally, DSA keeps an array of switch trees (group of switches) global to 564the kernel, and attaches a ``dsa_switch`` structure to a tree on registration. 565The tree ID to which the switch is attached is determined by the first u32 566number of the ``dsa,member`` property of the switch's OF node (0 if missing). 567The switch ID within the tree is determined by the second u32 number of the 568same OF property (0 if missing). Registering multiple switches with the same 569switch ID and tree ID is illegal and will cause an error. Using platform data, 570a single switch and a single switch tree is permitted. 571 572In case of a tree with multiple switches, probing takes place asymmetrically. 573The first N-1 callers of ``dsa_register_switch()`` only add their ports to the 574port list of the tree (``dst->ports``), each port having a backpointer to its 575associated switch (``dp->ds``). Then, these switches exit their 576``dsa_register_switch()`` call early, because ``dsa_tree_setup_routing_table()`` 577has determined that the tree is not yet complete (not all ports referenced by 578DSA links are present in the tree's port list). The tree becomes complete when 579the last switch calls ``dsa_register_switch()``, and this triggers the effective 580continuation of initialization (including the call to ``ds->ops->setup()``) for 581all switches within that tree, all as part of the calling context of the last 582switch's probe function. 583 584The opposite of registration takes place when calling ``dsa_unregister_switch()``, 585which removes a switch's ports from the port list of the tree. The entire tree 586is torn down when the first switch unregisters. 587 588It is mandatory for DSA switch drivers to implement the ``shutdown()`` callback 589of their respective bus, and call ``dsa_switch_shutdown()`` from it (a minimal 590version of the full teardown performed by ``dsa_unregister_switch()``). 591The reason is that DSA keeps a reference on the conduit net device, and if the 592driver for the conduit device decides to unbind on shutdown, DSA's reference 593will block that operation from finalizing. 594 595Either ``dsa_switch_shutdown()`` or ``dsa_unregister_switch()`` must be called, 596but not both, and the device driver model permits the bus' ``remove()`` method 597to be called even if ``shutdown()`` was already called. Therefore, drivers are 598expected to implement a mutual exclusion method between ``remove()`` and 599``shutdown()`` by setting their drvdata to NULL after any of these has run, and 600checking whether the drvdata is NULL before proceeding to take any action. 601 602After ``dsa_switch_shutdown()`` or ``dsa_unregister_switch()`` was called, no 603further callbacks via the provided ``dsa_switch_ops`` may take place, and the 604driver may free the data structures associated with the ``dsa_switch``. 605 606Switch configuration 607-------------------- 608 609- ``get_tag_protocol``: this is to indicate what kind of tagging protocol is 610 supported, should be a valid value from the ``dsa_tag_protocol`` enum. 611 The returned information does not have to be static; the driver is passed the 612 CPU port number, as well as the tagging protocol of a possibly stacked 613 upstream switch, in case there are hardware limitations in terms of supported 614 tag formats. 615 616- ``change_tag_protocol``: when the default tagging protocol has compatibility 617 problems with the conduit or other issues, the driver may support changing it 618 at runtime, either through a device tree property or through sysfs. In that 619 case, further calls to ``get_tag_protocol`` should report the protocol in 620 current use. 621 622- ``setup``: setup function for the switch, this function is responsible for setting 623 up the ``dsa_switch_ops`` private structure with all it needs: register maps, 624 interrupts, mutexes, locks, etc. This function is also expected to properly 625 configure the switch to separate all network interfaces from each other, that 626 is, they should be isolated by the switch hardware itself, typically by creating 627 a Port-based VLAN ID for each port and allowing only the CPU port and the 628 specific port to be in the forwarding vector. Ports that are unused by the 629 platform should be disabled. Past this function, the switch is expected to be 630 fully configured and ready to serve any kind of request. It is recommended 631 to issue a software reset of the switch during this setup function in order to 632 avoid relying on what a previous software agent such as a bootloader/firmware 633 may have previously configured. The method responsible for undoing any 634 applicable allocations or operations done here is ``teardown``. 635 636- ``port_setup`` and ``port_teardown``: methods for initialization and 637 destruction of per-port data structures. It is mandatory for some operations 638 such as registering and unregistering devlink port regions to be done from 639 these methods, otherwise they are optional. A port will be torn down only if 640 it has been previously set up. It is possible for a port to be set up during 641 probing only to be torn down immediately afterwards, for example in case its 642 PHY cannot be found. In this case, probing of the DSA switch continues 643 without that particular port. 644 645- ``port_change_conduit``: method through which the affinity (association used 646 for traffic termination purposes) between a user port and a CPU port can be 647 changed. By default all user ports from a tree are assigned to the first 648 available CPU port that makes sense for them (most of the times this means 649 the user ports of a tree are all assigned to the same CPU port, except for H 650 topologies as described in commit 2c0b03258b8b). The ``port`` argument 651 represents the index of the user port, and the ``conduit`` argument represents 652 the new DSA conduit ``net_device``. The CPU port associated with the new 653 conduit can be retrieved by looking at ``struct dsa_port *cpu_dp = 654 conduit->dsa_ptr``. Additionally, the conduit can also be a LAG device where 655 all the slave devices are physical DSA conduits. LAG DSA also have a 656 valid ``conduit->dsa_ptr`` pointer, however this is not unique, but rather a 657 duplicate of the first physical DSA conduit's (LAG slave) ``dsa_ptr``. In case 658 of a LAG DSA conduit, a further call to ``port_lag_join`` will be emitted 659 separately for the physical CPU ports associated with the physical DSA 660 conduits, requesting them to create a hardware LAG associated with the LAG 661 interface. 662 663PHY devices and link management 664------------------------------- 665 666- ``get_phy_flags``: Some switches are interfaced to various kinds of Ethernet PHYs, 667 if the PHY library PHY driver needs to know about information it cannot obtain 668 on its own (e.g.: coming from switch memory mapped registers), this function 669 should return a 32-bit bitmask of "flags" that is private between the switch 670 driver and the Ethernet PHY driver in ``drivers/net/phy/\*``. 671 672- ``phy_read``: Function invoked by the DSA user MDIO bus when attempting to read 673 the switch port MDIO registers. If unavailable, return 0xffff for each read. 674 For builtin switch Ethernet PHYs, this function should allow reading the link 675 status, auto-negotiation results, link partner pages, etc. 676 677- ``phy_write``: Function invoked by the DSA user MDIO bus when attempting to write 678 to the switch port MDIO registers. If unavailable return a negative error 679 code. 680 681- ``adjust_link``: Function invoked by the PHY library when a user network device 682 is attached to a PHY device. This function is responsible for appropriately 683 configuring the switch port link parameters: speed, duplex, pause based on 684 what the ``phy_device`` is providing. 685 686- ``fixed_link_update``: Function invoked by the PHY library, and specifically by 687 the fixed PHY driver asking the switch driver for link parameters that could 688 not be auto-negotiated, or obtained by reading the PHY registers through MDIO. 689 This is particularly useful for specific kinds of hardware such as QSGMII, 690 MoCA or other kinds of non-MDIO managed PHYs where out of band link 691 information is obtained 692 693Ethtool operations 694------------------ 695 696- ``get_strings``: ethtool function used to query the driver's strings, will 697 typically return statistics strings, private flags strings, etc. 698 699- ``get_ethtool_stats``: ethtool function used to query per-port statistics and 700 return their values. DSA overlays user network devices general statistics: 701 RX/TX counters from the network device, with switch driver specific statistics 702 per port 703 704- ``get_sset_count``: ethtool function used to query the number of statistics items 705 706- ``get_wol``: ethtool function used to obtain Wake-on-LAN settings per-port, this 707 function may for certain implementations also query the conduit network device 708 Wake-on-LAN settings if this interface needs to participate in Wake-on-LAN 709 710- ``set_wol``: ethtool function used to configure Wake-on-LAN settings per-port, 711 direct counterpart to set_wol with similar restrictions 712 713- ``set_eee``: ethtool function which is used to configure a switch port EEE (Green 714 Ethernet) settings, can optionally invoke the PHY library to enable EEE at the 715 PHY level if relevant. This function should enable EEE at the switch port MAC 716 controller and data-processing logic 717 718- ``get_eee``: ethtool function which is used to query a switch port EEE settings, 719 this function should return the EEE state of the switch port MAC controller 720 and data-processing logic as well as query the PHY for its currently configured 721 EEE settings 722 723- ``get_eeprom_len``: ethtool function returning for a given switch the EEPROM 724 length/size in bytes 725 726- ``get_eeprom``: ethtool function returning for a given switch the EEPROM contents 727 728- ``set_eeprom``: ethtool function writing specified data to a given switch EEPROM 729 730- ``get_regs_len``: ethtool function returning the register length for a given 731 switch 732 733- ``get_regs``: ethtool function returning the Ethernet switch internal register 734 contents. This function might require user-land code in ethtool to 735 pretty-print register values and registers 736 737Power management 738---------------- 739 740- ``suspend``: function invoked by the DSA platform device when the system goes to 741 suspend, should quiesce all Ethernet switch activities, but keep ports 742 participating in Wake-on-LAN active as well as additional wake-up logic if 743 supported 744 745- ``resume``: function invoked by the DSA platform device when the system resumes, 746 should resume all Ethernet switch activities and re-configure the switch to be 747 in a fully active state 748 749- ``port_enable``: function invoked by the DSA user network device ndo_open 750 function when a port is administratively brought up, this function should 751 fully enable a given switch port. DSA takes care of marking the port with 752 ``BR_STATE_BLOCKING`` if the port is a bridge member, or ``BR_STATE_FORWARDING`` if it 753 was not, and propagating these changes down to the hardware 754 755- ``port_disable``: function invoked by the DSA user network device ndo_close 756 function when a port is administratively brought down, this function should 757 fully disable a given switch port. DSA takes care of marking the port with 758 ``BR_STATE_DISABLED`` and propagating changes to the hardware if this port is 759 disabled while being a bridge member 760 761Address databases 762----------------- 763 764Switching hardware is expected to have a table for FDB entries, however not all 765of them are active at the same time. An address database is the subset (partition) 766of FDB entries that is active (can be matched by address learning on RX, or FDB 767lookup on TX) depending on the state of the port. An address database may 768occasionally be called "FID" (Filtering ID) in this document, although the 769underlying implementation may choose whatever is available to the hardware. 770 771For example, all ports that belong to a VLAN-unaware bridge (which is 772*currently* VLAN-unaware) are expected to learn source addresses in the 773database associated by the driver with that bridge (and not with other 774VLAN-unaware bridges). During forwarding and FDB lookup, a packet received on a 775VLAN-unaware bridge port should be able to find a VLAN-unaware FDB entry having 776the same MAC DA as the packet, which is present on another port member of the 777same bridge. At the same time, the FDB lookup process must be able to not find 778an FDB entry having the same MAC DA as the packet, if that entry points towards 779a port which is a member of a different VLAN-unaware bridge (and is therefore 780associated with a different address database). 781 782Similarly, each VLAN of each offloaded VLAN-aware bridge should have an 783associated address database, which is shared by all ports which are members of 784that VLAN, but not shared by ports belonging to different bridges that are 785members of the same VID. 786 787In this context, a VLAN-unaware database means that all packets are expected to 788match on it irrespective of VLAN ID (only MAC address lookup), whereas a 789VLAN-aware database means that packets are supposed to match based on the VLAN 790ID from the classified 802.1Q header (or the pvid if untagged). 791 792At the bridge layer, VLAN-unaware FDB entries have the special VID value of 0, 793whereas VLAN-aware FDB entries have non-zero VID values. Note that a 794VLAN-unaware bridge may have VLAN-aware (non-zero VID) FDB entries, and a 795VLAN-aware bridge may have VLAN-unaware FDB entries. As in hardware, the 796software bridge keeps separate address databases, and offloads to hardware the 797FDB entries belonging to these databases, through switchdev, asynchronously 798relative to the moment when the databases become active or inactive. 799 800When a user port operates in standalone mode, its driver should configure it to 801use a separate database called a port private database. This is different from 802the databases described above, and should impede operation as standalone port 803(packet in, packet out to the CPU port) as little as possible. For example, 804on ingress, it should not attempt to learn the MAC SA of ingress traffic, since 805learning is a bridging layer service and this is a standalone port, therefore 806it would consume useless space. With no address learning, the port private 807database should be empty in a naive implementation, and in this case, all 808received packets should be trivially flooded to the CPU port. 809 810DSA (cascade) and CPU ports are also called "shared" ports because they service 811multiple address databases, and the database that a packet should be associated 812to is usually embedded in the DSA tag. This means that the CPU port may 813simultaneously transport packets coming from a standalone port (which were 814classified by hardware in one address database), and from a bridge port (which 815were classified to a different address database). 816 817Switch drivers which satisfy certain criteria are able to optimize the naive 818configuration by removing the CPU port from the flooding domain of the switch, 819and just program the hardware with FDB entries pointing towards the CPU port 820for which it is known that software is interested in those MAC addresses. 821Packets which do not match a known FDB entry will not be delivered to the CPU, 822which will save CPU cycles required for creating an skb just to drop it. 823 824DSA is able to perform host address filtering for the following kinds of 825addresses: 826 827- Primary unicast MAC addresses of ports (``dev->dev_addr``). These are 828 associated with the port private database of the respective user port, 829 and the driver is notified to install them through ``port_fdb_add`` towards 830 the CPU port. 831 832- Secondary unicast and multicast MAC addresses of ports (addresses added 833 through ``dev_uc_add()`` and ``dev_mc_add()``). These are also associated 834 with the port private database of the respective user port. 835 836- Local/permanent bridge FDB entries (``BR_FDB_LOCAL``). These are the MAC 837 addresses of the bridge ports, for which packets must be terminated locally 838 and not forwarded. They are associated with the address database for that 839 bridge. 840 841- Static bridge FDB entries installed towards foreign (non-DSA) interfaces 842 present in the same bridge as some DSA switch ports. These are also 843 associated with the address database for that bridge. 844 845- Dynamically learned FDB entries on foreign interfaces present in the same 846 bridge as some DSA switch ports, only if ``ds->assisted_learning_on_cpu_port`` 847 is set to true by the driver. These are associated with the address database 848 for that bridge. 849 850For various operations detailed below, DSA provides a ``dsa_db`` structure 851which can be of the following types: 852 853- ``DSA_DB_PORT``: the FDB (or MDB) entry to be installed or deleted belongs to 854 the port private database of user port ``db->dp``. 855- ``DSA_DB_BRIDGE``: the entry belongs to one of the address databases of bridge 856 ``db->bridge``. Separation between the VLAN-unaware database and the per-VID 857 databases of this bridge is expected to be done by the driver. 858- ``DSA_DB_LAG``: the entry belongs to the address database of LAG ``db->lag``. 859 Note: ``DSA_DB_LAG`` is currently unused and may be removed in the future. 860 861The drivers which act upon the ``dsa_db`` argument in ``port_fdb_add``, 862``port_mdb_add`` etc should declare ``ds->fdb_isolation`` as true. 863 864DSA associates each offloaded bridge and each offloaded LAG with a one-based ID 865(``struct dsa_bridge :: num``, ``struct dsa_lag :: id``) for the purposes of 866refcounting addresses on shared ports. Drivers may piggyback on DSA's numbering 867scheme (the ID is readable through ``db->bridge.num`` and ``db->lag.id`` or may 868implement their own. 869 870Only the drivers which declare support for FDB isolation are notified of FDB 871entries on the CPU port belonging to ``DSA_DB_PORT`` databases. 872For compatibility/legacy reasons, ``DSA_DB_BRIDGE`` addresses are notified to 873drivers even if they do not support FDB isolation. However, ``db->bridge.num`` 874and ``db->lag.id`` are always set to 0 in that case (to denote the lack of 875isolation, for refcounting purposes). 876 877Note that it is not mandatory for a switch driver to implement physically 878separate address databases for each standalone user port. Since FDB entries in 879the port private databases will always point to the CPU port, there is no risk 880for incorrect forwarding decisions. In this case, all standalone ports may 881share the same database, but the reference counting of host-filtered addresses 882(not deleting the FDB entry for a port's MAC address if it's still in use by 883another port) becomes the responsibility of the driver, because DSA is unaware 884that the port databases are in fact shared. This can be achieved by calling 885``dsa_fdb_present_in_other_db()`` and ``dsa_mdb_present_in_other_db()``. 886The down side is that the RX filtering lists of each user port are in fact 887shared, which means that user port A may accept a packet with a MAC DA it 888shouldn't have, only because that MAC address was in the RX filtering list of 889user port B. These packets will still be dropped in software, however. 890 891Bridge layer 892------------ 893 894Offloading the bridge forwarding plane is optional and handled by the methods 895below. They may be absent, return -EOPNOTSUPP, or ``ds->max_num_bridges`` may 896be non-zero and exceeded, and in this case, joining a bridge port is still 897possible, but the packet forwarding will take place in software, and the ports 898under a software bridge must remain configured in the same way as for 899standalone operation, i.e. have all bridging service functions (address 900learning etc) disabled, and send all received packets to the CPU port only. 901 902Concretely, a port starts offloading the forwarding plane of a bridge once it 903returns success to the ``port_bridge_join`` method, and stops doing so after 904``port_bridge_leave`` has been called. Offloading the bridge means autonomously 905learning FDB entries in accordance with the software bridge port's state, and 906autonomously forwarding (or flooding) received packets without CPU intervention. 907This is optional even when offloading a bridge port. Tagging protocol drivers 908are expected to call ``dsa_default_offload_fwd_mark(skb)`` for packets which 909have already been autonomously forwarded in the forwarding domain of the 910ingress switch port. DSA, through ``dsa_port_devlink_setup()``, considers all 911switch ports part of the same tree ID to be part of the same bridge forwarding 912domain (capable of autonomous forwarding to each other). 913 914Offloading the TX forwarding process of a bridge is a distinct concept from 915simply offloading its forwarding plane, and refers to the ability of certain 916driver and tag protocol combinations to transmit a single skb coming from the 917bridge device's transmit function to potentially multiple egress ports (and 918thereby avoid its cloning in software). 919 920Packets for which the bridge requests this behavior are called data plane 921packets and have ``skb->offload_fwd_mark`` set to true in the tag protocol 922driver's ``xmit`` function. Data plane packets are subject to FDB lookup, 923hardware learning on the CPU port, and do not override the port STP state. 924Additionally, replication of data plane packets (multicast, flooding) is 925handled in hardware and the bridge driver will transmit a single skb for each 926packet that may or may not need replication. 927 928When the TX forwarding offload is enabled, the tag protocol driver is 929responsible to inject packets into the data plane of the hardware towards the 930correct bridging domain (FID) that the port is a part of. The port may be 931VLAN-unaware, and in this case the FID must be equal to the FID used by the 932driver for its VLAN-unaware address database associated with that bridge. 933Alternatively, the bridge may be VLAN-aware, and in that case, it is guaranteed 934that the packet is also VLAN-tagged with the VLAN ID that the bridge processed 935this packet in. It is the responsibility of the hardware to untag the VID on 936the egress-untagged ports, or keep the tag on the egress-tagged ones. 937 938- ``port_bridge_join``: bridge layer function invoked when a given switch port is 939 added to a bridge, this function should do what's necessary at the switch 940 level to permit the joining port to be added to the relevant logical 941 domain for it to ingress/egress traffic with other members of the bridge. 942 By setting the ``tx_fwd_offload`` argument to true, the TX forwarding process 943 of this bridge is also offloaded. 944 945- ``port_bridge_leave``: bridge layer function invoked when a given switch port is 946 removed from a bridge, this function should do what's necessary at the 947 switch level to deny the leaving port from ingress/egress traffic from the 948 remaining bridge members. 949 950- ``port_stp_state_set``: bridge layer function invoked when a given switch port STP 951 state is computed by the bridge layer and should be propagated to switch 952 hardware to forward/block/learn traffic. 953 954- ``port_bridge_flags``: bridge layer function invoked when a port must 955 configure its settings for e.g. flooding of unknown traffic or source address 956 learning. The switch driver is responsible for initial setup of the 957 standalone ports with address learning disabled and egress flooding of all 958 types of traffic, then the DSA core notifies of any change to the bridge port 959 flags when the port joins and leaves a bridge. DSA does not currently manage 960 the bridge port flags for the CPU port. The assumption is that address 961 learning should be statically enabled (if supported by the hardware) on the 962 CPU port, and flooding towards the CPU port should also be enabled, due to a 963 lack of an explicit address filtering mechanism in the DSA core. 964 965- ``port_fast_age``: bridge layer function invoked when flushing the 966 dynamically learned FDB entries on the port is necessary. This is called when 967 transitioning from an STP state where learning should take place to an STP 968 state where it shouldn't, or when leaving a bridge, or when address learning 969 is turned off via ``port_bridge_flags``. 970 971Bridge VLAN filtering 972--------------------- 973 974- ``port_vlan_filtering``: bridge layer function invoked when the bridge gets 975 configured for turning on or off VLAN filtering. If nothing specific needs to 976 be done at the hardware level, this callback does not need to be implemented. 977 When VLAN filtering is turned on, the hardware must be programmed with 978 rejecting 802.1Q frames which have VLAN IDs outside of the programmed allowed 979 VLAN ID map/rules. If there is no PVID programmed into the switch port, 980 untagged frames must be rejected as well. When turned off the switch must 981 accept any 802.1Q frames irrespective of their VLAN ID, and untagged frames are 982 allowed. 983 984- ``port_vlan_add``: bridge layer function invoked when a VLAN is configured 985 (tagged or untagged) for the given switch port. The CPU port becomes a member 986 of a VLAN only if a foreign bridge port is also a member of it (and 987 forwarding needs to take place in software), or the VLAN is installed to the 988 VLAN group of the bridge device itself, for termination purposes 989 (``bridge vlan add dev br0 vid 100 self``). VLANs on shared ports are 990 reference counted and removed when there is no user left. Drivers do not need 991 to manually install a VLAN on the CPU port. 992 993- ``port_vlan_del``: bridge layer function invoked when a VLAN is removed from the 994 given switch port 995 996- ``port_fdb_add``: bridge layer function invoked when the bridge wants to install a 997 Forwarding Database entry, the switch hardware should be programmed with the 998 specified address in the specified VLAN Id in the forwarding database 999 associated with this VLAN ID. 1000 1001- ``port_fdb_del``: bridge layer function invoked when the bridge wants to remove a 1002 Forwarding Database entry, the switch hardware should be programmed to delete 1003 the specified MAC address from the specified VLAN ID if it was mapped into 1004 this port forwarding database 1005 1006- ``port_fdb_dump``: bridge bypass function invoked by ``ndo_fdb_dump`` on the 1007 physical DSA port interfaces. Since DSA does not attempt to keep in sync its 1008 hardware FDB entries with the software bridge, this method is implemented as 1009 a means to view the entries visible on user ports in the hardware database. 1010 The entries reported by this function have the ``self`` flag in the output of 1011 the ``bridge fdb show`` command. 1012 1013- ``port_mdb_add``: bridge layer function invoked when the bridge wants to install 1014 a multicast database entry. The switch hardware should be programmed with the 1015 specified address in the specified VLAN ID in the forwarding database 1016 associated with this VLAN ID. 1017 1018- ``port_mdb_del``: bridge layer function invoked when the bridge wants to remove a 1019 multicast database entry, the switch hardware should be programmed to delete 1020 the specified MAC address from the specified VLAN ID if it was mapped into 1021 this port forwarding database. 1022 1023Link aggregation 1024---------------- 1025 1026Link aggregation is implemented in the Linux networking stack by the bonding 1027and team drivers, which are modeled as virtual, stackable network interfaces. 1028DSA is capable of offloading a link aggregation group (LAG) to hardware that 1029supports the feature, and supports bridging between physical ports and LAGs, 1030as well as between LAGs. A bonding/team interface which holds multiple physical 1031ports constitutes a logical port, although DSA has no explicit concept of a 1032logical port at the moment. Due to this, events where a LAG joins/leaves a 1033bridge are treated as if all individual physical ports that are members of that 1034LAG join/leave the bridge. Switchdev port attributes (VLAN filtering, STP 1035state, etc) and objects (VLANs, MDB entries) offloaded to a LAG as bridge port 1036are treated similarly: DSA offloads the same switchdev object / port attribute 1037on all members of the LAG. Static bridge FDB entries on a LAG are not yet 1038supported, since the DSA driver API does not have the concept of a logical port 1039ID. 1040 1041- ``port_lag_join``: function invoked when a given switch port is added to a 1042 LAG. The driver may return ``-EOPNOTSUPP``, and in this case, DSA will fall 1043 back to a software implementation where all traffic from this port is sent to 1044 the CPU. 1045- ``port_lag_leave``: function invoked when a given switch port leaves a LAG 1046 and returns to operation as a standalone port. 1047- ``port_lag_change``: function invoked when the link state of any member of 1048 the LAG changes, and the hashing function needs rebalancing to only make use 1049 of the subset of physical LAG member ports that are up. 1050 1051Drivers that benefit from having an ID associated with each offloaded LAG 1052can optionally populate ``ds->num_lag_ids`` from the ``dsa_switch_ops::setup`` 1053method. The LAG ID associated with a bonding/team interface can then be 1054retrieved by a DSA switch driver using the ``dsa_lag_id`` function. 1055 1056IEC 62439-2 (MRP) 1057----------------- 1058 1059The Media Redundancy Protocol is a topology management protocol optimized for 1060fast fault recovery time for ring networks, which has some components 1061implemented as a function of the bridge driver. MRP uses management PDUs 1062(Test, Topology, LinkDown/Up, Option) sent at a multicast destination MAC 1063address range of 01:15:4e:00:00:0x and with an EtherType of 0x88e3. 1064Depending on the node's role in the ring (MRM: Media Redundancy Manager, 1065MRC: Media Redundancy Client, MRA: Media Redundancy Automanager), certain MRP 1066PDUs might need to be terminated locally and others might need to be forwarded. 1067An MRM might also benefit from offloading to hardware the creation and 1068transmission of certain MRP PDUs (Test). 1069 1070Normally an MRP instance can be created on top of any network interface, 1071however in the case of a device with an offloaded data path such as DSA, it is 1072necessary for the hardware, even if it is not MRP-aware, to be able to extract 1073the MRP PDUs from the fabric before the driver can proceed with the software 1074implementation. DSA today has no driver which is MRP-aware, therefore it only 1075listens for the bare minimum switchdev objects required for the software assist 1076to work properly. The operations are detailed below. 1077 1078- ``port_mrp_add`` and ``port_mrp_del``: notifies driver when an MRP instance 1079 with a certain ring ID, priority, primary port and secondary port is 1080 created/deleted. 1081- ``port_mrp_add_ring_role`` and ``port_mrp_del_ring_role``: function invoked 1082 when an MRP instance changes ring roles between MRM or MRC. This affects 1083 which MRP PDUs should be trapped to software and which should be autonomously 1084 forwarded. 1085 1086IEC 62439-3 (HSR/PRP) 1087--------------------- 1088 1089The Parallel Redundancy Protocol (PRP) is a network redundancy protocol which 1090works by duplicating and sequence numbering packets through two independent L2 1091networks (which are unaware of the PRP tail tags carried in the packets), and 1092eliminating the duplicates at the receiver. The High-availability Seamless 1093Redundancy (HSR) protocol is similar in concept, except all nodes that carry 1094the redundant traffic are aware of the fact that it is HSR-tagged (because HSR 1095uses a header with an EtherType of 0x892f) and are physically connected in a 1096ring topology. Both HSR and PRP use supervision frames for monitoring the 1097health of the network and for discovery of other nodes. 1098 1099In Linux, both HSR and PRP are implemented in the hsr driver, which 1100instantiates a virtual, stackable network interface with two member ports. 1101The driver only implements the basic roles of DANH (Doubly Attached Node 1102implementing HSR), DANP (Doubly Attached Node implementing PRP) and RedBox 1103(allows non-HSR devices to connect to the ring via Interlink ports). 1104 1105A driver which is able of offloading certain functions should declare the 1106corresponding netdev features as indicated by the documentation at 1107``Documentation/networking/netdev-features.rst``. Additionally, the following 1108methods must be implemented: 1109 1110- ``port_hsr_join``: function invoked when a given switch port is added to a 1111 DANP/DANH. The driver may return ``-EOPNOTSUPP`` and in this case, DSA will 1112 fall back to a software implementation where all traffic from this port is 1113 sent to the CPU. 1114- ``port_hsr_leave``: function invoked when a given switch port leaves a 1115 DANP/DANH and returns to normal operation as a standalone port. 1116 1117Note that the ``NETIF_F_HW_HSR_DUP`` feature relies on transmission towards 1118multiple ports, which is generally available whenever the tagging protocol uses 1119the ``dsa_xmit_port_mask()`` helper function. If the helper is used, the HSR 1120offload feature should also be set. The ``dsa_port_simple_hsr_join()`` and 1121``dsa_port_simple_hsr_leave()`` methods can be used as generic implementations 1122of ``port_hsr_join`` and ``port_hsr_leave``, if this is the only supported 1123offload feature. 1124 1125TODO 1126==== 1127 1128Making SWITCHDEV and DSA converge towards an unified codebase 1129------------------------------------------------------------- 1130 1131SWITCHDEV properly takes care of abstracting the networking stack with offload 1132capable hardware, but does not enforce a strict switch device driver model. On 1133the other DSA enforces a fairly strict device driver model, and deals with most 1134of the switch specific. At some point we should envision a merger between these 1135two subsystems and get the best of both worlds. 1136