1 .. SPDX-License-Identifier: GPL-2.0 2 .. _phy_link_topology: 3 4 ================= 5 PHY link topology 6 ================= 7 8 Overview 9 ======== 10 11 The PHY link topology representation in the networking stack aims at representing 12 the hardware layout for any given Ethernet link. 13 14 An Ethernet interface from userspace's point of view is nothing but a 15 :c:type:`struct net_device <net_device>`, which exposes configuration options 16 through the legacy ioctls and the ethtool netlink commands. The base assumption 17 when designing these configuration APIs were that the link looks something like :: 18 19 +-----------------------+ +----------+ +--------------+ 20 | Ethernet Controller / | | Ethernet | | Connector / | 21 | MAC | ------ | PHY | ---- | Port | ---... to LP 22 +-----------------------+ +----------+ +--------------+ 23 struct net_device struct phy_device 24 25 Commands that needs to configure the PHY will go through the net_device.phydev 26 field to reach the PHY and perform the relevant configuration. 27 28 This assumption falls apart in more complex topologies that can arise when, 29 for example, using SFP transceivers (although that's not the only specific case). 30 31 Here, we have 2 basic scenarios. Either the MAC is able to output a serialized 32 interface, that can directly be fed to an SFP cage, such as SGMII, 1000BaseX, 33 10GBaseR, etc. 34 35 The link topology then looks like this (when an SFP module is inserted) :: 36 37 +-----+ SGMII +------------+ 38 | MAC | ------- | SFP Module | 39 +-----+ +------------+ 40 41 Knowing that some modules embed a PHY, the actual link is more like :: 42 43 +-----+ SGMII +--------------+ 44 | MAC | -------- | PHY (on SFP) | 45 +-----+ +--------------+ 46 47 In this case, the SFP PHY is handled by phylib, and registered by phylink through 48 its SFP upstream ops. 49 50 Now some Ethernet controllers aren't able to output a serialized interface, so 51 we can't directly connect them to an SFP cage. However, some PHYs can be used 52 as media-converters, to translate the non-serialized MAC MII interface to a 53 serialized MII interface fed to the SFP :: 54 55 +-----+ RGMII +-----------------------+ SGMII +--------------+ 56 | MAC | ------- | PHY (media converter) | ------- | PHY (on SFP) | 57 +-----+ +-----------------------+ +--------------+ 58 59 This is where the model of having a single net_device.phydev pointer shows its 60 limitations, as we now have 2 PHYs on the link. 61 62 The phy_link topology framework aims at providing a way to keep track of every 63 PHY on the link, for use by both kernel drivers and subsystems, but also to 64 report the topology to userspace, allowing to target individual PHYs in configuration 65 commands. 66 67 API 68 === 69 70 The :c:type:`struct phy_link_topology <phy_link_topology>` is a per-netdevice 71 resource, that gets initialized at netdevice creation. Once it's initialized, 72 it is then possible to register PHYs to the topology through : 73 74 :c:func:`phy_link_topo_add_phy` 75 76 Besides registering the PHY to the topology, this call will also assign a unique 77 index to the PHY, which can then be reported to userspace to refer to this PHY 78 (akin to the ifindex). This index is a u32, ranging from 1 to U32_MAX. The value 79 0 is reserved to indicate the PHY doesn't belong to any topology yet. 80 81 The PHY can then be removed from the topology through 82 83 :c:func:`phy_link_topo_del_phy` 84 85 These function are already hooked into the phylib subsystem, so all PHYs that 86 are linked to a net_device through :c:func:`phy_attach_direct` will automatically 87 join the netdev's topology. 88 89 PHYs that are on a SFP module will also be automatically registered IF the SFP 90 upstream is phylink (so, no media-converter). 91 92 PHY drivers that can be used as SFP upstream need to call :c:func:`phy_sfp_attach_phy` 93 and :c:func:`phy_sfp_detach_phy`, which can be used as a 94 .attach_phy / .detach_phy implementation for the 95 :c:type:`struct sfp_upstream_ops <sfp_upstream_ops>`. 96 97 UAPI 98 ==== 99 100 There exist a set of netlink commands to query the link topology from userspace, 101 see ``Documentation/networking/ethtool-netlink.rst``. 102 103 The whole point of having a topology representation is to assign the phyindex 104 field in :c:type:`struct phy_device <phy_device>`. This index is reported to 105 userspace using the ``ETHTOOL_MSG_PHY_GET`` ethtnl command. Performing a DUMP operation 106 will result in all PHYs from all net_device being listed. The DUMP command 107 accepts either a ``ETHTOOL_A_HEADER_DEV_INDEX`` or ``ETHTOOL_A_HEADER_DEV_NAME`` 108 to be passed in the request to filter the DUMP to a single net_device. 109 110 The retrieved index can then be passed as a request parameter using the 111 ``ETHTOOL_A_HEADER_PHY_INDEX`` field in the following ethnl commands : 112 113 * ``ETHTOOL_MSG_STRSET_GET`` to get the stats string set from a given PHY 114 * ``ETHTOOL_MSG_CABLE_TEST_ACT`` and ``ETHTOOL_MSG_CABLE_TEST_ACT``, to perform 115 cable testing on a given PHY on the link (most likely the outermost PHY) 116 * ``ETHTOOL_MSG_PSE_SET`` and ``ETHTOOL_MSG_PSE_GET`` for PHY-controlled PoE and PSE settings 117 * ``ETHTOOL_MSG_PLCA_GET_CFG``, ``ETHTOOL_MSG_PLCA_SET_CFG`` and ``ETHTOOL_MSG_PLCA_GET_STATUS`` 118 to set the PLCA (Physical Layer Collision Avoidance) parameters 119 120 Note that the PHY index can be passed to other requests, which will silently 121 ignore it if present and irrelevant.
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