networking/dsa/dsa.rst

22 An Ethernet switch is typically comprised of multiple front-panel ports, and one
23 or more CPU or management port. The DSA subsystem currently relies on the
27 gateways, or even top-of-the rack switches. This host Ethernet controller will
31 with the ability to configure and manage cascaded switches on top of each other
36 For each front-panel port, DSA will create specialized network devices which are
37 used as controlling and data-flowing endpoints for use by the Linux networking
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
66 ------------------------
68 DSA currently supports 5 different tagging protocols, and a tag-less mode as
71 - ``net/dsa/tag_trailer.c``: Marvell's 4 trailer tag mode (legacy)
72 - ``net/dsa/tag_dsa.c``: Marvell's original DSA tag
73 - ``net/dsa/tag_edsa.c``: Marvell's enhanced DSA tag
74 - ``net/dsa/tag_brcm.c``: Broadcom's 4 bytes tag
75 - ``net/dsa/tag_qca.c``: Qualcomm's 2 bytes tag
80 - identifies which port the Ethernet frame came from/should be sent to
81 - provides a reason why this frame was forwarded to the management interface
84 ----------------------
96 ----------------------
101 specific (and fake) Ethernet type (later becoming ``skb->protocol``) with the
109         - receive function is invoked
110         - basic packet processing is done: getting length, status etc.
111         - packet is prepared to be processed by the Ethernet layer by calling
117                   if (dev->dsa_ptr != NULL)
118                           -> skb->protocol = ETH_P_XDSA
123                   -> iterate over registered packet_type
124                           -> invoke handler for ETH_P_XDSA, calls dsa_switch_rcv()
128           -> dsa_switch_rcv()
129                   -> invoke switch tag specific protocol handler in 'net/dsa/tag_*.c'
133         - inspect and strip switch tag protocol to determine originating port
134         - locate per-port network device
135         - invoke ``eth_type_trans()`` with the DSA slave network device
136         - invoked ``netif_receive_skb()``
142 ---------------------
144 Slave network devices created by DSA are stacked on top of their master network
146 controlling and data-flowing end-point for each front-panel port of the switch.
149 - insert/remove the switch tag protocol (if it exists) when sending traffic
151 - query the switch for ethtool operations: statistics, link state,
152   Wake-on-LAN, register dumps...
153 - external/internal PHY management: link, auto-negotiation etc.
170 ------------------------
176                 |---------------------------
178                 ----------------------------
183         |--------------------------------------------|
185         |--------------------------------------------|
187               |-------|  |-------|  |-------|
189               |-------|  |-------|  |-------|
194 --------------
196 In order to be able to read to/from a switch PHY built into it, DSA creates a
198 MDIO reads/writes towards specific PHY addresses. In most MDIO-connected
199 switches, these functions would utilize direct or indirect PHY addressing mode
200 to return standard MII registers from the switch builtin PHYs, allowing the PHY
201 library and/or to return link status, link partner pages, auto-negotiation
210 ---------------
215 - ``dsa_chip_data``: platform data configuration for a given switch device,
220 - ``dsa_platform_data``: platform device configuration data which can reference
225 - ``dsa_switch_tree``: structure assigned to the master network device under
232 - ``dsa_switch``: structure describing a switch device in the tree, referencing
236 - ``dsa_switch_ops``: structure referencing function pointers, see below for a
242 Limits on the number of devices and ports
243 -----------------------------------------
251 -------------------------------
256 - inability to fetch switch CPU port statistics counters using ethtool, which
259 - inability to configure the CPU port link parameters based on the Ethernet
262 - inability to configure specific VLAN IDs / trunking VLANs between switches
266 --------------------------------
268 Once a master network device is configured to use DSA (dev->dsa_ptr becomes
269 non-NULL), and the switch behind it expects a tagging protocol, this network
273 the Ethernet switch on the other end, expecting a tag will typically drop this
285 - MDIO/PHY library: ``drivers/net/phy/phy.c``, ``mdio_bus.c``
286 - Switchdev:``net/switchdev/*``
287 - Device Tree for various of_* functions
289 MDIO/PHY library
290 ----------------
292 Slave network devices exposed by DSA may or may not be interfacing with PHY
293 devices (``struct phy_device`` as defined in ``include/linux/phy.h)``, but the DSA
296 - internal PHY devices, built into the Ethernet switch hardware
297 - external PHY devices, connected via an internal or external MDIO bus
298 - internal PHY devices, connected via an internal MDIO bus
299 - special, non-autonegotiated or non MDIO-managed PHY devices: SFPs, MoCA; a.k.a
302 The PHY configuration is done by the ``dsa_slave_phy_setup()`` function and the
305 - if Device Tree is used, the PHY device is looked up using the standard
306   "phy-handle" property, if found, this PHY device is created and registered
309 - if Device Tree is used, and the PHY device is "fixed", that is, conforms to
310   the definition of a non-MDIO managed PHY as defined in
311   ``Documentation/devicetree/bindings/net/fixed-link.txt``, the PHY is registered
314 - finally, if the PHY is built into the switch, as is very common with
315   standalone switch packages, the PHY is probed using the slave MII bus created
320 ---------
323 more specifically with its VLAN filtering portion when configuring VLANs on top
324 of per-port slave network devices. Since DSA primarily deals with
325 MDIO-connected switches, although not exclusively, SWITCHDEV's
334 -----------
337 ``Documentation/devicetree/bindings/net/dsa/dsa.txt``. PHY/MDIO library helper
339 per-port PHY specific details: interface connection, MDIO bus location etc..
354 --------------------
356 - ``tag_protocol``: this is to indicate what kind of tagging protocol is supported,
359 - ``probe``: probe routine which will be invoked by the DSA platform device upon
362   the switch pseudo-PHY and return whether this is a supported device. For other
363   buses, return a non-NULL string
365 - ``setup``: setup function for the switch, this function is responsible for setting
370   a Port-based VLAN ID for each port and allowing only the CPU port and the
374   to issue a software reset of the switch during this setup function in order to
375   avoid relying on what a previous software agent such as a bootloader/firmware
378 PHY devices and link management
379 -------------------------------
381 - ``get_phy_flags``: Some switches are interfaced to various kinds of Ethernet PHYs,
382   if the PHY library PHY driver needs to know about information it cannot obtain
383   on its own (e.g.: coming from switch memory mapped registers), this function
384   should return a 32-bits bitmask of "flags", that is private between the switch
385   driver and the Ethernet PHY driver in ``drivers/net/phy/\*``.
387 - ``phy_read``: Function invoked by the DSA slave MDIO bus when attempting to read
390   status, auto-negotiation results, link partner pages etc..
392 - ``phy_write``: Function invoked by the DSA slave MDIO bus when attempting to write
396 - ``adjust_link``: Function invoked by the PHY library when a slave network device
397   is attached to a PHY device. This function is responsible for appropriately
398   configuring the switch port link parameters: speed, duplex, pause based on
401 - ``fixed_link_update``: Function invoked by the PHY library, and specifically by
402   the fixed PHY driver asking the switch driver for link parameters that could
403   not be auto-negotiated, or obtained by reading the PHY registers through MDIO.
405   MoCA or other kinds of non-MDIO managed PHYs where out of band link
409 ------------------
411 - ``get_strings``: ethtool function used to query the driver's strings, will
414 - ``get_ethtool_stats``: ethtool function used to query per-port statistics and
419 - ``get_sset_count``: ethtool function used to query the number of statistics items
421 - ``get_wol``: ethtool function used to obtain Wake-on-LAN settings per-port, this
423   Wake-on-LAN settings if this interface needs to participate in Wake-on-LAN
425 - ``set_wol``: ethtool function used to configure Wake-on-LAN settings per-port,
428 - ``set_eee``: ethtool function which is used to configure a switch port EEE (Green
429   Ethernet) settings, can optionally invoke the PHY library to enable EEE at the
430   PHY level if relevant. This function should enable EEE at the switch port MAC
431   controller and data-processing logic
433 - ``get_eee``: ethtool function which is used to query a switch port EEE settings,
435   and data-processing logic as well as query the PHY for its currently configured
438 - ``get_eeprom_len``: ethtool function returning for a given switch the EEPROM
441 - ``get_eeprom``: ethtool function returning for a given switch the EEPROM contents
443 - ``set_eeprom``: ethtool function writing specified data to a given switch EEPROM
445 - ``get_regs_len``: ethtool function returning the register length for a given
448 - ``get_regs``: ethtool function returning the Ethernet switch internal register
449   contents. This function might require user-land code in ethtool to
450   pretty-print register values and registers
453 ----------------
455 - ``suspend``: function invoked by the DSA platform device when the system goes to
457   participating in Wake-on-LAN active as well as additional wake-up logic if
460 - ``resume``: function invoked by the DSA platform device when the system resumes,
461   should resume all Ethernet switch activities and re-configure the switch to be
464 - ``port_enable``: function invoked by the DSA slave network device ndo_open
470 - ``port_disable``: function invoked by the DSA slave network device ndo_close
477 ------------
479 - ``port_bridge_join``: bridge layer function invoked when a given switch port is
484 - ``port_bridge_leave``: bridge layer function invoked when a given switch port is
491 - ``port_stp_state_set``: bridge layer function invoked when a given switch port STP
494   computing a STP state change based on current and asked parameters and perform
495   the relevant ageing based on the intersection results
498 ---------------------
500 - ``port_vlan_filtering``: bridge layer function invoked when the bridge gets
501   configured for turning on or off VLAN filtering. If nothing specific needs to
503   When VLAN filtering is turned on, the hardware must be programmed with
510 - ``port_vlan_prepare``: bridge layer function invoked when the bridge prepares the
511   configuration of a VLAN on the given port. If the operation is not supported
512   by the hardware, this function should return ``-EOPNOTSUPP`` to inform the bridge
516 - ``port_vlan_add``: bridge layer function invoked when a VLAN is configured
519 - ``port_vlan_del``: bridge layer function invoked when a VLAN is removed from the
522 - ``port_vlan_dump``: bridge layer function invoked with a switchdev callback
526 - ``port_fdb_add``: bridge layer function invoked when the bridge wants to install a
530   function should return ``-EOPNOTSUPP`` to inform the bridge code to fallback to
534         of DSA, would be its port-based VLAN, used by the associated bridge device.
536 - ``port_fdb_del``: bridge layer function invoked when the bridge wants to remove a
541 - ``port_fdb_dump``: bridge layer function invoked with a switchdev callback
545 - ``port_mdb_prepare``: bridge layer function invoked when the bridge prepares the
547   this function should return ``-EOPNOTSUPP`` to inform the bridge code to fallback
551 - ``port_mdb_add``: bridge layer function invoked when the bridge wants to install
557         of DSA, would be its port-based VLAN, used by the associated bridge device.
559 - ``port_mdb_del``: bridge layer function invoked when the bridge wants to remove a
564 - ``port_mdb_dump``: bridge layer function invoked with a switchdev callback
572 -------------------------------------------------------------
575 capable hardware, but does not enforce a strict switch device driver model. On
581 --------------------
583 - making the number of ports fully dynamic and not dependent on ``DSA_MAX_PORTS``
584 - allowing more than one CPU/management interface:
586 - porting more drivers from other vendors: