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diff --git a/Documentation/networking/dsa/dsa.rst b/Documentation/networking/dsa/dsa.rst index 563d56c6a25c..a94ddf83348a 100644 --- a/Documentation/networking/dsa/dsa.rst +++ b/Documentation/networking/dsa/dsa.rst @@ -10,21 +10,21 @@ in joining the effort. Design principles ================= -The Distributed Switch Architecture is a subsystem which was primarily designed -to support Marvell Ethernet switches (MV88E6xxx, a.k.a Linkstreet product line) -using Linux, but has since evolved to support other vendors as well. +The Distributed Switch Architecture subsystem was primarily designed to +support Marvell Ethernet switches (MV88E6xxx, a.k.a. Link Street product +line) using Linux, but has since evolved to support other vendors as well. The original philosophy behind this design was to be able to use unmodified Linux tools such as bridge, iproute2, ifconfig to work transparently whether they configured/queried a switch port network device or a regular network device. -An Ethernet switch is typically comprised of multiple front-panel ports, and one -or more CPU or management port. The DSA subsystem currently relies on the +An Ethernet switch typically comprises multiple front-panel ports and one +or more CPU or management ports. The DSA subsystem currently relies on the presence of a management port connected to an Ethernet controller capable of receiving Ethernet frames from the switch. This is a very common setup for all kinds of Ethernet switches found in Small Home and Office products: routers, -gateways, or even top-of-the rack switches. This host Ethernet controller will +gateways, or even top-of-rack switches. This host Ethernet controller will be later referred to as "master" and "cpu" in DSA terminology and code. The D in DSA stands for Distributed, because the subsystem has been designed @@ -33,14 +33,14 @@ using upstream and downstream Ethernet links between switches. These specific ports are referred to as "dsa" ports in DSA terminology and code. A collection of multiple switches connected to each other is called a "switch tree". -For each front-panel port, DSA will create specialized network devices which are +For each front-panel port, DSA creates specialized network devices which are used as controlling and data-flowing endpoints for use by the Linux networking stack. These specialized network interfaces are referred to as "slave" network interfaces in DSA terminology and code. The ideal case for using DSA is when an Ethernet switch supports a "switch tag" which is a hardware feature making the switch insert a specific tag for each -Ethernet frames it received to/from specific ports to help the management +Ethernet frame it receives to/from specific ports to help the management interface figure out: - what port is this frame coming from @@ -65,14 +65,8 @@ Note that DSA does not currently create network interfaces for the "cpu" and Switch tagging protocols ------------------------ -DSA currently supports 5 different tagging protocols, and a tag-less mode as -well. The different protocols are implemented in: - -- ``net/dsa/tag_trailer.c``: Marvell's 4 trailer tag mode (legacy) -- ``net/dsa/tag_dsa.c``: Marvell's original DSA tag -- ``net/dsa/tag_edsa.c``: Marvell's enhanced DSA tag -- ``net/dsa/tag_brcm.c``: Broadcom's 4 bytes tag -- ``net/dsa/tag_qca.c``: Qualcomm's 2 bytes tag +DSA supports many vendor-specific tagging protocols, one software-defined +tagging protocol, and a tag-less mode as well (``DSA_TAG_PROTO_NONE``). The exact format of the tag protocol is vendor specific, but in general, they all contain something which: @@ -80,6 +74,149 @@ all contain something which: - identifies which port the Ethernet frame came from/should be sent to - provides a reason why this frame was forwarded to the management interface +All tagging protocols are in ``net/dsa/tag_*.c`` files and implement the +methods of the ``struct dsa_device_ops`` structure, which are detailed below. + +Tagging protocols generally fall in one of three categories: + +1. The switch-specific frame header is located before the Ethernet header, + shifting to the right (from the perspective of the DSA master's frame + parser) the MAC DA, MAC SA, EtherType and the entire L2 payload. +2. The switch-specific frame header is located before the EtherType, keeping + the MAC DA and MAC SA in place from the DSA master's perspective, but + shifting the 'real' EtherType and L2 payload to the right. +3. The switch-specific frame header is located at the tail of the packet, + keeping all frame headers in place and not altering the view of the packet + that the DSA master's frame parser has. + +A tagging protocol may tag all packets with switch tags of the same length, or +the tag length might vary (for example packets with PTP timestamps might +require an extended switch tag, or there might be one tag length on TX and a +different one on RX). Either way, the tagging protocol driver must populate the +``struct dsa_device_ops::needed_headroom`` and/or ``struct dsa_device_ops::needed_tailroom`` +with the length in octets of the longest switch frame header/trailer. The DSA +framework will automatically adjust the MTU of the master interface to +accommodate for this extra size in order for DSA user ports to support the +standard MTU (L2 payload length) of 1500 octets. The ``needed_headroom`` and +``needed_tailroom`` properties are also used to request from the network stack, +on a best-effort basis, the allocation of packets with enough extra space such +that the act of pushing the switch tag on transmission of a packet does not +cause it to reallocate due to lack of memory. + +Even though applications are not expected to parse DSA-specific frame headers, +the format on the wire of the tagging protocol represents an Application Binary +Interface exposed by the kernel towards user space, for decoders such as +``libpcap``. The tagging protocol driver must populate the ``proto`` member of +``struct dsa_device_ops`` with a value that uniquely describes the +characteristics of the interaction required between the switch hardware and the +data path driver: the offset of each bit field within the frame header and any +stateful processing required to deal with the frames (as may be required for +PTP timestamping). + +From the perspective of the network stack, all switches within the same DSA +switch tree use the same tagging protocol. In case of a packet transiting a +fabric with more than one switch, the switch-specific frame header is inserted +by the first switch in the fabric that the packet was received on. This header +typically contains information regarding its type (whether it is a control +frame that must be trapped to the CPU, or a data frame to be forwarded). +Control frames should be decapsulated only by the software data path, whereas +data frames might also be autonomously forwarded towards other user ports of +other switches from the same fabric, and in this case, the outermost switch +ports must decapsulate the packet. + +Note that in certain cases, it might be the case that the tagging format used +by a leaf switch (not connected directly to the CPU) is not the same as what +the network stack sees. This can be seen with Marvell switch trees, where the +CPU port can be configured to use either the DSA or the Ethertype DSA (EDSA) +format, but the DSA links are configured to use the shorter (without Ethertype) +DSA frame header, in order to reduce the autonomous packet forwarding overhead. +It still remains the case that, if the DSA switch tree is configured for the +EDSA tagging protocol, the operating system sees EDSA-tagged packets from the +leaf switches that tagged them with the shorter DSA header. This can be done +because the Marvell switch connected directly to the CPU is configured to +perform tag translation between DSA and EDSA (which is simply the operation of +adding or removing the ``ETH_P_EDSA`` EtherType and some padding octets). + +It is possible to construct cascaded setups of DSA switches even if their +tagging protocols are not compatible with one another. In this case, there are +no DSA links in this fabric, and each switch constitutes a disjoint DSA switch +tree. The DSA links are viewed as simply a pair of a DSA master (the out-facing +port of the upstream DSA switch) and a CPU port (the in-facing port of the +downstream DSA switch). + +The tagging protocol of the attached DSA switch tree can be viewed through the +``dsa/tagging`` sysfs attribute of the DSA master:: + + cat /sys/class/net/eth0/dsa/tagging + +If the hardware and driver are capable, the tagging protocol of the DSA switch +tree can be changed at runtime. This is done by writing the new tagging +protocol name to the same sysfs device attribute as above (the DSA master and +all attached switch ports must be down while doing this). + +It is desirable that all tagging protocols are testable with the ``dsa_loop`` +mockup driver, which can be attached to any network interface. The goal is that +any network interface should be capable of transmitting the same packet in the +same way, and the tagger should decode the same received packet in the same way +regardless of the driver used for the switch control path, and the driver used +for the DSA master. + +The transmission of a packet goes through the tagger's ``xmit`` function. +The passed ``struct sk_buff *skb`` has ``skb->data`` pointing at +``skb_mac_header(skb)``, i.e. at the destination MAC address, and the passed +``struct net_device *dev`` represents the virtual DSA user network interface +whose hardware counterpart the packet must be steered to (i.e. ``swp0``). +The job of this method is to prepare the skb in a way that the switch will +understand what egress port the packet is for (and not deliver it towards other +ports). Typically this is fulfilled by pushing a frame header. Checking for +insufficient size in the skb headroom or tailroom is unnecessary provided that +the ``needed_headroom`` and ``needed_tailroom`` properties were filled out +properly, because DSA ensures there is enough space before calling this method. + +The reception of a packet goes through the tagger's ``rcv`` function. The +passed ``struct sk_buff *skb`` has ``skb->data`` pointing at +``skb_mac_header(skb) + ETH_ALEN`` octets, i.e. to where the first octet after +the EtherType would have been, were this frame not tagged. The role of this +method is to consume the frame header, adjust ``skb->data`` to really point at +the first octet after the EtherType, and to change ``skb->dev`` to point to the +virtual DSA user network interface corresponding to the physical front-facing +switch port that the packet was received on. + +Since tagging protocols in category 1 and 2 break software (and most often also +hardware) packet dissection on the DSA master, features such as RPS (Receive +Packet Steering) on the DSA master would be broken. The DSA framework deals +with this by hooking into the flow dissector and shifting the offset at which +the IP header is to be found in the tagged frame as seen by the DSA master. +This behavior is automatic based on the ``overhead`` value of the tagging +protocol. If not all packets are of equal size, the tagger can implement the +``flow_dissect`` method of the ``struct dsa_device_ops`` and override this +default behavior by specifying the correct offset incurred by each individual +RX packet. Tail taggers do not cause issues to the flow dissector. + +Checksum offload should work with category 1 and 2 taggers when the DSA master +driver declares NETIF_F_HW_CSUM in vlan_features and looks at csum_start and +csum_offset. For those cases, DSA will shift the checksum start and offset by +the tag size. If the DSA master driver still uses the legacy NETIF_F_IP_CSUM +or NETIF_F_IPV6_CSUM in vlan_features, the offload might only work if the +offload hardware already expects that specific tag (perhaps due to matching +vendors). DSA slaves inherit those flags from the master port, and it is up to +the driver to correctly fall back to software checksum when the IP header is not +where the hardware expects. If that check is ineffective, the packets might go +to the network without a proper checksum (the checksum field will have the +pseudo IP header sum). For category 3, when the offload hardware does not +already expect the switch tag in use, the checksum must be calculated before any +tag is inserted (i.e. inside the tagger). Otherwise, the DSA master would +include the tail tag in the (software or hardware) checksum calculation. Then, +when the tag gets stripped by the switch during transmission, it will leave an +incorrect IP checksum in place. + +Due to various reasons (most common being category 1 taggers being associated +with DSA-unaware masters, mangling what the master perceives as MAC DA), the +tagging protocol may require the DSA master to operate in promiscuous mode, to +receive all frames regardless of the value of the MAC DA. This can be done by +setting the ``promisc_on_master`` property of the ``struct dsa_device_ops``. +Note that this assumes a DSA-unaware master driver, which is the norm. + Master network devices ---------------------- @@ -95,7 +232,7 @@ Ethernet switch. Networking stack hooks ---------------------- -When a master netdev is used with DSA, a small hook is placed in in the +When a master netdev is used with DSA, a small hook is placed in the networking stack is in order to have the DSA subsystem process the Ethernet switch specific tagging protocol. DSA accomplishes this by registering a specific (and fake) Ethernet type (later becoming ``skb->protocol``) with the @@ -150,21 +287,35 @@ These interfaces are specialized in order to: to/from specific switch ports - query the switch for ethtool operations: statistics, link state, Wake-on-LAN, register dumps... -- external/internal PHY management: link, auto-negotiation etc. +- manage external/internal PHY: link, auto-negotiation, etc. These slave network devices have custom net_device_ops and ethtool_ops function pointers which allow DSA to introduce a level of layering between the networking -stack/ethtool, and the switch driver implementation. +stack/ethtool and the switch driver implementation. Upon frame transmission from these slave network devices, DSA will look up which -switch tagging protocol is currently registered with these network devices, and +switch tagging protocol is currently registered with these network devices and invoke a specific transmit routine which takes care of adding the relevant switch tag in the Ethernet frames. These frames are then queued for transmission using the master network device -``ndo_start_xmit()`` function, since they contain the appropriate switch tag, the +``ndo_start_xmit()`` function. Since they contain the appropriate switch tag, the Ethernet switch will be able to process these incoming frames from the -management interface and delivers these frames to the physical switch port. +management interface and deliver them to the physical switch port. + +When using multiple CPU ports, it is possible to stack a LAG (bonding/team) +device between the DSA slave devices and the physical DSA masters. The LAG +device is thus also a DSA master, but the LAG slave devices continue to be DSA +masters as well (just with no user port assigned to them; this is needed for +recovery in case the LAG DSA master disappears). Thus, the data path of the LAG +DSA master is used asymmetrically. On RX, the ``ETH_P_XDSA`` handler, which +calls ``dsa_switch_rcv()``, is invoked early (on the physical DSA master; +LAG slave). Therefore, the RX data path of the LAG DSA master is not used. +On the other hand, TX takes place linearly: ``dsa_slave_xmit`` calls +``dsa_enqueue_skb``, which calls ``dev_queue_xmit`` towards the LAG DSA master. +The latter calls ``dev_queue_xmit`` towards one physical DSA master or the +other, and in both cases, the packet exits the system through a hardware path +towards the switch. Graphical representation ------------------------ @@ -172,23 +323,34 @@ Graphical representation Summarized, this is basically how DSA looks like from a network device perspective:: - - |--------------------------- - | CPU network device (eth0)| - ---------------------------- - | <tag added by switch | - | | - | | - | tag added by CPU> | - |--------------------------------------------| - | Switch driver | - |--------------------------------------------| - || || || - |-------| |-------| |-------| - | sw0p0 | | sw0p1 | | sw0p2 | - |-------| |-------| |-------| - - + Unaware application + opens and binds socket + | ^ + | | + +-----------v--|--------------------+ + |+------+ +------+ +------+ +------+| + || swp0 | | swp1 | | swp2 | | swp3 || + |+------+-+------+-+------+-+------+| + | DSA switch driver | + +-----------------------------------+ + | ^ + Tag added by | | Tag consumed by + switch driver | | switch driver + v | + +-----------------------------------+ + | Unmodified host interface driver | Software + --------+-----------------------------------+------------ + | Host interface (eth0) | Hardware + +-----------------------------------+ + | ^ + Tag consumed by | | Tag added by + switch hardware | | switch hardware + v | + +-----------------------------------+ + | Switch | + |+------+ +------+ +------+ +------+| + || swp0 | | swp1 | | swp2 | | swp3 || + ++------+-+------+-+------+-+------++ Slave MDIO bus -------------- @@ -199,9 +361,9 @@ MDIO reads/writes towards specific PHY addresses. In most MDIO-connected switches, these functions would utilize direct or indirect PHY addressing mode to return standard MII registers from the switch builtin PHYs, allowing the PHY library and/or to return link status, link partner pages, auto-negotiation -results etc.. +results, etc. -For Ethernet switches which have both external and internal MDIO busses, the +For Ethernet switches which have both external and internal MDIO buses, the slave MII bus can be utilized to mux/demux MDIO reads and writes towards either internal or external MDIO devices this switch might be connected to: internal PHYs, external PHYs, or even external switches. @@ -218,7 +380,7 @@ DSA data structures are defined in ``include/net/dsa.h`` as well as table indication (when cascading switches) - ``dsa_platform_data``: platform device configuration data which can reference - a collection of dsa_chip_data structure if multiples switches are cascaded, + a collection of dsa_chip_data structures if multiple switches are cascaded, the master network device this switch tree is attached to needs to be referenced @@ -239,14 +401,6 @@ DSA data structures are defined in ``include/net/dsa.h`` as well as Design limitations ================== -Limits on the number of devices and ports ------------------------------------------ - -DSA currently limits the number of maximum switches within a tree to 4 -(``DSA_MAX_SWITCHES``), and the number of ports per switch to 12 (``DSA_MAX_PORTS``). -These limits could be extended to support larger configurations would this need -arise. - Lack of CPU/DSA network devices ------------------------------- @@ -273,10 +427,6 @@ will not make us go through the switch tagging protocol transmit function, so the Ethernet switch on the other end, expecting a tag will typically drop this frame. -Slave network devices check that the master network device is UP before allowing -you to administratively bring UP these slave network devices. A common -configuration mistake is forgetting to bring UP the master network device first. - Interactions with other subsystems ================================== @@ -285,6 +435,7 @@ DSA currently leverages the following subsystems: - MDIO/PHY library: ``drivers/net/phy/phy.c``, ``mdio_bus.c`` - Switchdev:``net/switchdev/*`` - Device Tree for various of_* functions +- Devlink: ``net/core/devlink.c`` MDIO/PHY library ---------------- @@ -306,7 +457,7 @@ logic basically looks like this: "phy-handle" property, if found, this PHY device is created and registered using ``of_phy_connect()`` -- if Device Tree is used, and the PHY device is "fixed", that is, conforms to +- if Device Tree is used and the PHY device is "fixed", that is, conforms to the definition of a non-MDIO managed PHY as defined in ``Documentation/devicetree/bindings/net/fixed-link.txt``, the PHY is registered and connected transparently using the special fixed MDIO bus driver @@ -321,14 +472,39 @@ SWITCHDEV DSA directly utilizes SWITCHDEV when interfacing with the bridge layer, and more specifically with its VLAN filtering portion when configuring VLANs on top -of per-port slave network devices. Since DSA primarily deals with -MDIO-connected switches, although not exclusively, SWITCHDEV's -prepare/abort/commit phases are often simplified into a prepare phase which -checks whether the operation is supported by the DSA switch driver, and a commit -phase which applies the changes. - -As of today, the only SWITCHDEV objects supported by DSA are the FDB and VLAN -objects. +of per-port slave network devices. As of today, the only SWITCHDEV objects +supported by DSA are the FDB and VLAN objects. + +Devlink +------- + +DSA registers one devlink device per physical switch in the fabric. +For each devlink device, every physical port (i.e. user ports, CPU ports, DSA +links or unused ports) is exposed as a devlink port. + +DSA drivers can make use of the following devlink features: + +- Regions: debugging feature which allows user space to dump driver-defined + areas of hardware information in a low-level, binary format. Both global + regions as well as per-port regions are supported. It is possible to export + devlink regions even for pieces of data that are already exposed in some way + to the standard iproute2 user space programs (ip-link, bridge), like address + tables and VLAN tables. For example, this might be useful if the tables + contain additional hardware-specific details which are not visible through + the iproute2 abstraction, or it might be useful to inspect these tables on + the non-user ports too, which are invisible to iproute2 because no network + interface is registered for them. +- Params: a feature which enables user to configure certain low-level tunable + knobs pertaining to the device. Drivers may implement applicable generic + devlink params, or may add new device-specific devlink params. +- Resources: a monitoring feature which enables users to see the degree of + utilization of certain hardware tables in the device, such as FDB, VLAN, etc. +- Shared buffers: a QoS feature for adjusting and partitioning memory and frame + reservations per port and per traffic class, in the ingress and egress + directions, such that low-priority bulk traffic does not impede the + processing of high-priority critical traffic. + +For more details, consult ``Documentation/networking/devlink/``. Device Tree ----------- @@ -336,35 +512,117 @@ Device Tree DSA features a standardized binding which is documented in ``Documentation/devicetree/bindings/net/dsa/dsa.txt``. PHY/MDIO library helper functions such as ``of_get_phy_mode()``, ``of_phy_connect()`` are also used to query -per-port PHY specific details: interface connection, MDIO bus location etc.. +per-port PHY specific details: interface connection, MDIO bus location, etc. Driver development ================== -DSA switch drivers need to implement a dsa_switch_ops structure which will +DSA switch drivers need to implement a ``dsa_switch_ops`` structure which will contain the various members described below. -``register_switch_driver()`` registers this dsa_switch_ops in its internal list -of drivers to probe for. ``unregister_switch_driver()`` does the exact opposite. +Probing, registration and device lifetime +----------------------------------------- + +DSA switches are regular ``device`` structures on buses (be they platform, SPI, +I2C, MDIO or otherwise). The DSA framework is not involved in their probing +with the device core. + +Switch registration from the perspective of a driver means passing a valid +``struct dsa_switch`` pointer to ``dsa_register_switch()``, usually from the +switch driver's probing function. The following members must be valid in the +provided structure: + +- ``ds->dev``: will be used to parse the switch's OF node or platform data. + +- ``ds->num_ports``: will be used to create the port list for this switch, and + to validate the port indices provided in the OF node. + +- ``ds->ops``: a pointer to the ``dsa_switch_ops`` structure holding the DSA + method implementations. + +- ``ds->priv``: backpointer to a driver-private data structure which can be + retrieved in all further DSA method callbacks. + +In addition, the following flags in the ``dsa_switch`` structure may optionally +be configured to obtain driver-specific behavior from the DSA core. Their +behavior when set is documented through comments in ``include/net/dsa.h``. + +- ``ds->vlan_filtering_is_global`` + +- ``ds->needs_standalone_vlan_filtering`` + +- ``ds->configure_vlan_while_not_filtering`` + +- ``ds->untag_bridge_pvid`` + +- ``ds->assisted_learning_on_cpu_port`` -Unless requested differently by setting the priv_size member accordingly, DSA -does not allocate any driver private context space. +- ``ds->mtu_enforcement_ingress`` + +- ``ds->fdb_isolation`` + +Internally, DSA keeps an array of switch trees (group of switches) global to +the kernel, and attaches a ``dsa_switch`` structure to a tree on registration. +The tree ID to which the switch is attached is determined by the first u32 +number of the ``dsa,member`` property of the switch's OF node (0 if missing). +The switch ID within the tree is determined by the second u32 number of the +same OF property (0 if missing). Registering multiple switches with the same +switch ID and tree ID is illegal and will cause an error. Using platform data, +a single switch and a single switch tree is permitted. + +In case of a tree with multiple switches, probing takes place asymmetrically. +The first N-1 callers of ``dsa_register_switch()`` only add their ports to the +port list of the tree (``dst->ports``), each port having a backpointer to its +associated switch (``dp->ds``). Then, these switches exit their +``dsa_register_switch()`` call early, because ``dsa_tree_setup_routing_table()`` +has determined that the tree is not yet complete (not all ports referenced by +DSA links are present in the tree's port list). The tree becomes complete when +the last switch calls ``dsa_register_switch()``, and this triggers the effective +continuation of initialization (including the call to ``ds->ops->setup()``) for +all switches within that tree, all as part of the calling context of the last +switch's probe function. + +The opposite of registration takes place when calling ``dsa_unregister_switch()``, +which removes a switch's ports from the port list of the tree. The entire tree +is torn down when the first switch unregisters. + +It is mandatory for DSA switch drivers to implement the ``shutdown()`` callback +of their respective bus, and call ``dsa_switch_shutdown()`` from it (a minimal +version of the full teardown performed by ``dsa_unregister_switch()``). +The reason is that DSA keeps a reference on the master net device, and if the +driver for the master device decides to unbind on shutdown, DSA's reference +will block that operation from finalizing. + +Either ``dsa_switch_shutdown()`` or ``dsa_unregister_switch()`` must be called, +but not both, and the device driver model permits the bus' ``remove()`` method +to be called even if ``shutdown()`` was already called. Therefore, drivers are +expected to implement a mutual exclusion method between ``remove()`` and +``shutdown()`` by setting their drvdata to NULL after any of these has run, and +checking whether the drvdata is NULL before proceeding to take any action. + +After ``dsa_switch_shutdown()`` or ``dsa_unregister_switch()`` was called, no +further callbacks via the provided ``dsa_switch_ops`` may take place, and the +driver may free the data structures associated with the ``dsa_switch``. Switch configuration -------------------- -- ``tag_protocol``: this is to indicate what kind of tagging protocol is supported, - should be a valid value from the ``dsa_tag_protocol`` enum +- ``get_tag_protocol``: this is to indicate what kind of tagging protocol is + supported, should be a valid value from the ``dsa_tag_protocol`` enum. + The returned information does not have to be static; the driver is passed the + CPU port number, as well as the tagging protocol of a possibly stacked + upstream switch, in case there are hardware limitations in terms of supported + tag formats. -- ``probe``: probe routine which will be invoked by the DSA platform device upon - registration to test for the presence/absence of a switch device. For MDIO - devices, it is recommended to issue a read towards internal registers using - the switch pseudo-PHY and return whether this is a supported device. For other - buses, return a non-NULL string +- ``change_tag_protocol``: when the default tagging protocol has compatibility + problems with the master or other issues, the driver may support changing it + at runtime, either through a device tree property or through sysfs. In that + case, further calls to ``get_tag_protocol`` should report the protocol in + current use. - ``setup``: setup function for the switch, this function is responsible for setting up the ``dsa_switch_ops`` private structure with all it needs: register maps, - interrupts, mutexes, locks etc.. This function is also expected to properly + interrupts, mutexes, locks, etc. This function is also expected to properly configure the switch to separate all network interfaces from each other, that is, they should be isolated by the switch hardware itself, typically by creating a Port-based VLAN ID for each port and allowing only the CPU port and the @@ -373,7 +631,35 @@ Switch configuration fully configured and ready to serve any kind of request. It is recommended to issue a software reset of the switch during this setup function in order to avoid relying on what a previous software agent such as a bootloader/firmware - may have previously configured. + may have previously configured. The method responsible for undoing any + applicable allocations or operations done here is ``teardown``. + +- ``port_setup`` and ``port_teardown``: methods for initialization and + destruction of per-port data structures. It is mandatory for some operations + such as registering and unregistering devlink port regions to be done from + these methods, otherwise they are optional. A port will be torn down only if + it has been previously set up. It is possible for a port to be set up during + probing only to be torn down immediately afterwards, for example in case its + PHY cannot be found. In this case, probing of the DSA switch continues + without that particular port. + +- ``port_change_master``: method through which the affinity (association used + for traffic termination purposes) between a user port and a CPU port can be + changed. By default all user ports from a tree are assigned to the first + available CPU port that makes sense for them (most of the times this means + the user ports of a tree are all assigned to the same CPU port, except for H + topologies as described in commit 2c0b03258b8b). The ``port`` argument + represents the index of the user port, and the ``master`` argument represents + the new DSA master ``net_device``. The CPU port associated with the new + master can be retrieved by looking at ``struct dsa_port *cpu_dp = + master->dsa_ptr``. Additionally, the master can also be a LAG device where + all the slave devices are physical DSA masters. LAG DSA masters also have a + valid ``master->dsa_ptr`` pointer, however this is not unique, but rather a + duplicate of the first physical DSA master's (LAG slave) ``dsa_ptr``. In case + of a LAG DSA master, a further call to ``port_lag_join`` will be emitted + separately for the physical CPU ports associated with the physical DSA + masters, requesting them to create a hardware LAG associated with the LAG + interface. PHY devices and link management ------------------------------- @@ -381,13 +667,13 @@ PHY devices and link management - ``get_phy_flags``: Some switches are interfaced to various kinds of Ethernet PHYs, if the PHY library PHY driver needs to know about information it cannot obtain on its own (e.g.: coming from switch memory mapped registers), this function - should return a 32-bits bitmask of "flags", that is private between the switch + should return a 32-bit bitmask of "flags" that is private between the switch driver and the Ethernet PHY driver in ``drivers/net/phy/\*``. - ``phy_read``: Function invoked by the DSA slave MDIO bus when attempting to read the switch port MDIO registers. If unavailable, return 0xffff for each read. For builtin switch Ethernet PHYs, this function should allow reading the link - status, auto-negotiation results, link partner pages etc.. + status, auto-negotiation results, link partner pages, etc. - ``phy_write``: Function invoked by the DSA slave MDIO bus when attempting to write to the switch port MDIO registers. If unavailable return a negative error @@ -409,7 +695,7 @@ Ethtool operations ------------------ - ``get_strings``: ethtool function used to query the driver's strings, will - typically return statistics strings, private flags strings etc. + typically return statistics strings, private flags strings, etc. - ``get_ethtool_stats``: ethtool function used to query per-port statistics and return their values. DSA overlays slave network devices general statistics: @@ -419,7 +705,7 @@ Ethtool operations - ``get_sset_count``: ethtool function used to query the number of statistics items - ``get_wol``: ethtool function used to obtain Wake-on-LAN settings per-port, this - function may, for certain implementations also query the master network device + function may for certain implementations also query the master network device Wake-on-LAN settings if this interface needs to participate in Wake-on-LAN - ``set_wol``: ethtool function used to configure Wake-on-LAN settings per-port, @@ -462,37 +748,226 @@ Power management in a fully active state - ``port_enable``: function invoked by the DSA slave network device ndo_open - function when a port is administratively brought up, this function should be - fully enabling a given switch port. DSA takes care of marking the port with + function when a port is administratively brought up, this function should + fully enable a given switch port. DSA takes care of marking the port with ``BR_STATE_BLOCKING`` if the port is a bridge member, or ``BR_STATE_FORWARDING`` if it was not, and propagating these changes down to the hardware - ``port_disable``: function invoked by the DSA slave network device ndo_close - function when a port is administratively brought down, this function should be - fully disabling a given switch port. DSA takes care of marking the port with + function when a port is administratively brought down, this function should + fully disable a given switch port. DSA takes care of marking the port with ``BR_STATE_DISABLED`` and propagating changes to the hardware if this port is disabled while being a bridge member +Address databases +----------------- + +Switching hardware is expected to have a table for FDB entries, however not all +of them are active at the same time. An address database is the subset (partition) +of FDB entries that is active (can be matched by address learning on RX, or FDB +lookup on TX) depending on the state of the port. An address database may +occasionally be called "FID" (Filtering ID) in this document, although the +underlying implementation may choose whatever is available to the hardware. + +For example, all ports that belong to a VLAN-unaware bridge (which is +*currently* VLAN-unaware) are expected to learn source addresses in the +database associated by the driver with that bridge (and not with other +VLAN-unaware bridges). During forwarding and FDB lookup, a packet received on a +VLAN-unaware bridge port should be able to find a VLAN-unaware FDB entry having +the same MAC DA as the packet, which is present on another port member of the +same bridge. At the same time, the FDB lookup process must be able to not find +an FDB entry having the same MAC DA as the packet, if that entry points towards +a port which is a member of a different VLAN-unaware bridge (and is therefore +associated with a different address database). + +Similarly, each VLAN of each offloaded VLAN-aware bridge should have an +associated address database, which is shared by all ports which are members of +that VLAN, but not shared by ports belonging to different bridges that are +members of the same VID. + +In this context, a VLAN-unaware database means that all packets are expected to +match on it irrespective of VLAN ID (only MAC address lookup), whereas a +VLAN-aware database means that packets are supposed to match based on the VLAN +ID from the classified 802.1Q header (or the pvid if untagged). + +At the bridge layer, VLAN-unaware FDB entries have the special VID value of 0, +whereas VLAN-aware FDB entries have non-zero VID values. Note that a +VLAN-unaware bridge may have VLAN-aware (non-zero VID) FDB entries, and a +VLAN-aware bridge may have VLAN-unaware FDB entries. As in hardware, the +software bridge keeps separate address databases, and offloads to hardware the +FDB entries belonging to these databases, through switchdev, asynchronously +relative to the moment when the databases become active or inactive. + +When a user port operates in standalone mode, its driver should configure it to +use a separate database called a port private database. This is different from +the databases described above, and should impede operation as standalone port +(packet in, packet out to the CPU port) as little as possible. For example, +on ingress, it should not attempt to learn the MAC SA of ingress traffic, since +learning is a bridging layer service and this is a standalone port, therefore +it would consume useless space. With no address learning, the port private +database should be empty in a naive implementation, and in this case, all +received packets should be trivially flooded to the CPU port. + +DSA (cascade) and CPU ports are also called "shared" ports because they service +multiple address databases, and the database that a packet should be associated +to is usually embedded in the DSA tag. This means that the CPU port may +simultaneously transport packets coming from a standalone port (which were +classified by hardware in one address database), and from a bridge port (which +were classified to a different address database). + +Switch drivers which satisfy certain criteria are able to optimize the naive +configuration by removing the CPU port from the flooding domain of the switch, +and just program the hardware with FDB entries pointing towards the CPU port +for which it is known that software is interested in those MAC addresses. +Packets which do not match a known FDB entry will not be delivered to the CPU, +which will save CPU cycles required for creating an skb just to drop it. + +DSA is able to perform host address filtering for the following kinds of +addresses: + +- Primary unicast MAC addresses of ports (``dev->dev_addr``). These are + associated with the port private database of the respective user port, + and the driver is notified to install them through ``port_fdb_add`` towards + the CPU port. + +- Secondary unicast and multicast MAC addresses of ports (addresses added + through ``dev_uc_add()`` and ``dev_mc_add()``). These are also associated + with the port private database of the respective user port. + +- Local/permanent bridge FDB entries (``BR_FDB_LOCAL``). These are the MAC + addresses of the bridge ports, for which packets must be terminated locally + and not forwarded. They are associated with the address database for that + bridge. + +- Static bridge FDB entries installed towards foreign (non-DSA) interfaces + present in the same bridge as some DSA switch ports. These are also + associated with the address database for that bridge. + +- Dynamically learned FDB entries on foreign interfaces present in the same + bridge as some DSA switch ports, only if ``ds->assisted_learning_on_cpu_port`` + is set to true by the driver. These are associated with the address database + for that bridge. + +For various operations detailed below, DSA provides a ``dsa_db`` structure +which can be of the following types: + +- ``DSA_DB_PORT``: the FDB (or MDB) entry to be installed or deleted belongs to + the port private database of user port ``db->dp``. +- ``DSA_DB_BRIDGE``: the entry belongs to one of the address databases of bridge + ``db->bridge``. Separation between the VLAN-unaware database and the per-VID + databases of this bridge is expected to be done by the driver. +- ``DSA_DB_LAG``: the entry belongs to the address database of LAG ``db->lag``. + Note: ``DSA_DB_LAG`` is currently unused and may be removed in the future. + +The drivers which act upon the ``dsa_db`` argument in ``port_fdb_add``, +``port_mdb_add`` etc should declare ``ds->fdb_isolation`` as true. + +DSA associates each offloaded bridge and each offloaded LAG with a one-based ID +(``struct dsa_bridge :: num``, ``struct dsa_lag :: id``) for the purposes of +refcounting addresses on shared ports. Drivers may piggyback on DSA's numbering +scheme (the ID is readable through ``db->bridge.num`` and ``db->lag.id`` or may +implement their own. + +Only the drivers which declare support for FDB isolation are notified of FDB +entries on the CPU port belonging to ``DSA_DB_PORT`` databases. +For compatibility/legacy reasons, ``DSA_DB_BRIDGE`` addresses are notified to +drivers even if they do not support FDB isolation. However, ``db->bridge.num`` +and ``db->lag.id`` are always set to 0 in that case (to denote the lack of +isolation, for refcounting purposes). + +Note that it is not mandatory for a switch driver to implement physically +separate address databases for each standalone user port. Since FDB entries in +the port private databases will always point to the CPU port, there is no risk +for incorrect forwarding decisions. In this case, all standalone ports may +share the same database, but the reference counting of host-filtered addresses +(not deleting the FDB entry for a port's MAC address if it's still in use by +another port) becomes the responsibility of the driver, because DSA is unaware +that the port databases are in fact shared. This can be achieved by calling +``dsa_fdb_present_in_other_db()`` and ``dsa_mdb_present_in_other_db()``. +The down side is that the RX filtering lists of each user port are in fact +shared, which means that user port A may accept a packet with a MAC DA it +shouldn't have, only because that MAC address was in the RX filtering list of +user port B. These packets will still be dropped in software, however. + Bridge layer ------------ +Offloading the bridge forwarding plane is optional and handled by the methods +below. They may be absent, return -EOPNOTSUPP, or ``ds->max_num_bridges`` may +be non-zero and exceeded, and in this case, joining a bridge port is still +possible, but the packet forwarding will take place in software, and the ports +under a software bridge must remain configured in the same way as for +standalone operation, i.e. have all bridging service functions (address +learning etc) disabled, and send all received packets to the CPU port only. + +Concretely, a port starts offloading the forwarding plane of a bridge once it +returns success to the ``port_bridge_join`` method, and stops doing so after +``port_bridge_leave`` has been called. Offloading the bridge means autonomously +learning FDB entries in accordance with the software bridge port's state, and +autonomously forwarding (or flooding) received packets without CPU intervention. +This is optional even when offloading a bridge port. Tagging protocol drivers +are expected to call ``dsa_default_offload_fwd_mark(skb)`` for packets which +have already been autonomously forwarded in the forwarding domain of the +ingress switch port. DSA, through ``dsa_port_devlink_setup()``, considers all +switch ports part of the same tree ID to be part of the same bridge forwarding +domain (capable of autonomous forwarding to each other). + +Offloading the TX forwarding process of a bridge is a distinct concept from +simply offloading its forwarding plane, and refers to the ability of certain +driver and tag protocol combinations to transmit a single skb coming from the +bridge device's transmit function to potentially multiple egress ports (and +thereby avoid its cloning in software). + +Packets for which the bridge requests this behavior are called data plane +packets and have ``skb->offload_fwd_mark`` set to true in the tag protocol +driver's ``xmit`` function. Data plane packets are subject to FDB lookup, +hardware learning on the CPU port, and do not override the port STP state. +Additionally, replication of data plane packets (multicast, flooding) is +handled in hardware and the bridge driver will transmit a single skb for each +packet that may or may not need replication. + +When the TX forwarding offload is enabled, the tag protocol driver is +responsible to inject packets into the data plane of the hardware towards the +correct bridging domain (FID) that the port is a part of. The port may be +VLAN-unaware, and in this case the FID must be equal to the FID used by the +driver for its VLAN-unaware address database associated with that bridge. +Alternatively, the bridge may be VLAN-aware, and in that case, it is guaranteed +that the packet is also VLAN-tagged with the VLAN ID that the bridge processed +this packet in. It is the responsibility of the hardware to untag the VID on +the egress-untagged ports, or keep the tag on the egress-tagged ones. + - ``port_bridge_join``: bridge layer function invoked when a given switch port is - added to a bridge, this function should be doing the necessary at the switch - level to permit the joining port from being added to the relevant logical + added to a bridge, this function should do what's necessary at the switch + level to permit the joining port to be added to the relevant logical domain for it to ingress/egress traffic with other members of the bridge. + By setting the ``tx_fwd_offload`` argument to true, the TX forwarding process + of this bridge is also offloaded. - ``port_bridge_leave``: bridge layer function invoked when a given switch port is - removed from a bridge, this function should be doing the necessary at the + removed from a bridge, this function should do what's necessary at the switch level to deny the leaving port from ingress/egress traffic from the - remaining bridge members. When the port leaves the bridge, it should be aged - out at the switch hardware for the switch to (re) learn MAC addresses behind - this port. + remaining bridge members. - ``port_stp_state_set``: bridge layer function invoked when a given switch port STP state is computed by the bridge layer and should be propagated to switch - hardware to forward/block/learn traffic. The switch driver is responsible for - computing a STP state change based on current and asked parameters and perform - the relevant ageing based on the intersection results + hardware to forward/block/learn traffic. + +- ``port_bridge_flags``: bridge layer function invoked when a port must + configure its settings for e.g. flooding of unknown traffic or source address + learning. The switch driver is responsible for initial setup of the + standalone ports with address learning disabled and egress flooding of all + types of traffic, then the DSA core notifies of any change to the bridge port + flags when the port joins and leaves a bridge. DSA does not currently manage + the bridge port flags for the CPU port. The assumption is that address + learning should be statically enabled (if supported by the hardware) on the + CPU port, and flooding towards the CPU port should also be enabled, due to a + lack of an explicit address filtering mechanism in the DSA core. + +- ``port_fast_age``: bridge layer function invoked when flushing the + dynamically learned FDB entries on the port is necessary. This is called when + transitioning from an STP state where learning should take place to an STP + state where it shouldn't, or when leaving a bridge, or when address learning + is turned off via ``port_bridge_flags``. Bridge VLAN filtering --------------------- @@ -507,63 +982,139 @@ Bridge VLAN filtering accept any 802.1Q frames irrespective of their VLAN ID, and untagged frames are allowed. -- ``port_vlan_prepare``: bridge layer function invoked when the bridge prepares the - configuration of a VLAN on the given port. If the operation is not supported - by the hardware, this function should return ``-EOPNOTSUPP`` to inform the bridge - code to fallback to a software implementation. No hardware setup must be done - in this function. See port_vlan_add for this and details. - - ``port_vlan_add``: bridge layer function invoked when a VLAN is configured - (tagged or untagged) for the given switch port + (tagged or untagged) for the given switch port. The CPU port becomes a member + of a VLAN only if a foreign bridge port is also a member of it (and + forwarding needs to take place in software), or the VLAN is installed to the + VLAN group of the bridge device itself, for termination purposes + (``bridge vlan add dev br0 vid 100 self``). VLANs on shared ports are + reference counted and removed when there is no user left. Drivers do not need + to manually install a VLAN on the CPU port. - ``port_vlan_del``: bridge layer function invoked when a VLAN is removed from the given switch port -- ``port_vlan_dump``: bridge layer function invoked with a switchdev callback - function that the driver has to call for each VLAN the given port is a member - of. A switchdev object is used to carry the VID and bridge flags. - - ``port_fdb_add``: bridge layer function invoked when the bridge wants to install a Forwarding Database entry, the switch hardware should be programmed with the specified address in the specified VLAN Id in the forwarding database - associated with this VLAN ID. If the operation is not supported, this - function should return ``-EOPNOTSUPP`` to inform the bridge code to fallback to - a software implementation. - -.. note:: VLAN ID 0 corresponds to the port private database, which, in the context - of DSA, would be its port-based VLAN, used by the associated bridge device. + associated with this VLAN ID. - ``port_fdb_del``: bridge layer function invoked when the bridge wants to remove a Forwarding Database entry, the switch hardware should be programmed to delete the specified MAC address from the specified VLAN ID if it was mapped into this port forwarding database -- ``port_fdb_dump``: bridge layer function invoked with a switchdev callback - function that the driver has to call for each MAC address known to be behind - the given port. A switchdev object is used to carry the VID and FDB info. - -- ``port_mdb_prepare``: bridge layer function invoked when the bridge prepares the - installation of a multicast database entry. If the operation is not supported, - this function should return ``-EOPNOTSUPP`` to inform the bridge code to fallback - to a software implementation. No hardware setup must be done in this function. - See ``port_fdb_add`` for this and details. +- ``port_fdb_dump``: bridge bypass function invoked by ``ndo_fdb_dump`` on the + physical DSA port interfaces. Since DSA does not attempt to keep in sync its + hardware FDB entries with the software bridge, this method is implemented as + a means to view the entries visible on user ports in the hardware database. + The entries reported by this function have the ``self`` flag in the output of + the ``bridge fdb show`` command. - ``port_mdb_add``: bridge layer function invoked when the bridge wants to install - a multicast database entry, the switch hardware should be programmed with the + a multicast database entry. The switch hardware should be programmed with the specified address in the specified VLAN ID in the forwarding database associated with this VLAN ID. -.. note:: VLAN ID 0 corresponds to the port private database, which, in the context - of DSA, would be its port-based VLAN, used by the associated bridge device. - - ``port_mdb_del``: bridge layer function invoked when the bridge wants to remove a multicast database entry, the switch hardware should be programmed to delete the specified MAC address from the specified VLAN ID if it was mapped into this port forwarding database. -- ``port_mdb_dump``: bridge layer function invoked with a switchdev callback - function that the driver has to call for each MAC address known to be behind - the given port. A switchdev object is used to carry the VID and MDB info. +Link aggregation +---------------- + +Link aggregation is implemented in the Linux networking stack by the bonding +and team drivers, which are modeled as virtual, stackable network interfaces. +DSA is capable of offloading a link aggregation group (LAG) to hardware that +supports the feature, and supports bridging between physical ports and LAGs, +as well as between LAGs. A bonding/team interface which holds multiple physical +ports constitutes a logical port, although DSA has no explicit concept of a +logical port at the moment. Due to this, events where a LAG joins/leaves a +bridge are treated as if all individual physical ports that are members of that +LAG join/leave the bridge. Switchdev port attributes (VLAN filtering, STP +state, etc) and objects (VLANs, MDB entries) offloaded to a LAG as bridge port +are treated similarly: DSA offloads the same switchdev object / port attribute +on all members of the LAG. Static bridge FDB entries on a LAG are not yet +supported, since the DSA driver API does not have the concept of a logical port +ID. + +- ``port_lag_join``: function invoked when a given switch port is added to a + LAG. The driver may return ``-EOPNOTSUPP``, and in this case, DSA will fall + back to a software implementation where all traffic from this port is sent to + the CPU. +- ``port_lag_leave``: function invoked when a given switch port leaves a LAG + and returns to operation as a standalone port. +- ``port_lag_change``: function invoked when the link state of any member of + the LAG changes, and the hashing function needs rebalancing to only make use + of the subset of physical LAG member ports that are up. + +Drivers that benefit from having an ID associated with each offloaded LAG +can optionally populate ``ds->num_lag_ids`` from the ``dsa_switch_ops::setup`` +method. The LAG ID associated with a bonding/team interface can then be +retrieved by a DSA switch driver using the ``dsa_lag_id`` function. + +IEC 62439-2 (MRP) +----------------- + +The Media Redundancy Protocol is a topology management protocol optimized for +fast fault recovery time for ring networks, which has some components +implemented as a function of the bridge driver. MRP uses management PDUs +(Test, Topology, LinkDown/Up, Option) sent at a multicast destination MAC +address range of 01:15:4e:00:00:0x and with an EtherType of 0x88e3. +Depending on the node's role in the ring (MRM: Media Redundancy Manager, +MRC: Media Redundancy Client, MRA: Media Redundancy Automanager), certain MRP +PDUs might need to be terminated locally and others might need to be forwarded. +An MRM might also benefit from offloading to hardware the creation and +transmission of certain MRP PDUs (Test). + +Normally an MRP instance can be created on top of any network interface, +however in the case of a device with an offloaded data path such as DSA, it is +necessary for the hardware, even if it is not MRP-aware, to be able to extract +the MRP PDUs from the fabric before the driver can proceed with the software +implementation. DSA today has no driver which is MRP-aware, therefore it only +listens for the bare minimum switchdev objects required for the software assist +to work properly. The operations are detailed below. + +- ``port_mrp_add`` and ``port_mrp_del``: notifies driver when an MRP instance + with a certain ring ID, priority, primary port and secondary port is + created/deleted. +- ``port_mrp_add_ring_role`` and ``port_mrp_del_ring_role``: function invoked + when an MRP instance changes ring roles between MRM or MRC. This affects + which MRP PDUs should be trapped to software and which should be autonomously + forwarded. + +IEC 62439-3 (HSR/PRP) +--------------------- + +The Parallel Redundancy Protocol (PRP) is a network redundancy protocol which +works by duplicating and sequence numbering packets through two independent L2 +networks (which are unaware of the PRP tail tags carried in the packets), and +eliminating the duplicates at the receiver. The High-availability Seamless +Redundancy (HSR) protocol is similar in concept, except all nodes that carry +the redundant traffic are aware of the fact that it is HSR-tagged (because HSR +uses a header with an EtherType of 0x892f) and are physically connected in a +ring topology. Both HSR and PRP use supervision frames for monitoring the +health of the network and for discovery of other nodes. + +In Linux, both HSR and PRP are implemented in the hsr driver, which +instantiates a virtual, stackable network interface with two member ports. +The driver only implements the basic roles of DANH (Doubly Attached Node +implementing HSR) and DANP (Doubly Attached Node implementing PRP); the roles +of RedBox and QuadBox are not implemented (therefore, bridging a hsr network +interface with a physical switch port does not produce the expected result). + +A driver which is able of offloading certain functions of a DANP or DANH should +declare the corresponding netdev features as indicated by the documentation at +``Documentation/networking/netdev-features.rst``. Additionally, the following +methods must be implemented: + +- ``port_hsr_join``: function invoked when a given switch port is added to a + DANP/DANH. The driver may return ``-EOPNOTSUPP`` and in this case, DSA will + fall back to a software implementation where all traffic from this port is + sent to the CPU. +- ``port_hsr_leave``: function invoked when a given switch port leaves a + DANP/DANH and returns to normal operation as a standalone port. TODO ==== @@ -576,12 +1127,3 @@ capable hardware, but does not enforce a strict switch device driver model. On the other DSA enforces a fairly strict device driver model, and deals with most of the switch specific. At some point we should envision a merger between these two subsystems and get the best of both worlds. - -Other hanging fruits --------------------- - -- making the number of ports fully dynamic and not dependent on ``DSA_MAX_PORTS`` -- allowing more than one CPU/management interface: - http://comments.gmane.org/gmane.linux.network/365657 -- porting more drivers from other vendors: - http://comments.gmane.org/gmane.linux.network/365510 |