diff options
Diffstat (limited to 'Documentation/networking')
| -rw-r--r-- | Documentation/networking/ethtool-netlink.rst | 3 | ||||
| -rw-r--r-- | Documentation/networking/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/networking/phy-link-topology.rst | 121 |
3 files changed, 125 insertions, 0 deletions
diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst index 8c152871c23c..44cb9e29f325 100644 --- a/Documentation/networking/ethtool-netlink.rst +++ b/Documentation/networking/ethtool-netlink.rst @@ -2198,10 +2198,13 @@ Retrieve information about a given Ethernet PHY sitting on the link. The DO operation returns all available information about dev->phydev. User can also specify a PHY_INDEX, in which case the DO request returns information about that specific PHY. + As there can be more than one PHY, the DUMP operation can be used to list the PHYs present on a given interface, by passing an interface index or name in the dump request. +For more information, refer to :ref:`phy_link_topology` + Request contents: ==================================== ====== ========================== diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index d1af04b952f8..c71b87346178 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -91,6 +91,7 @@ Contents: operstates packet_mmap phonet + phy-link-topology pktgen plip ppp_generic diff --git a/Documentation/networking/phy-link-topology.rst b/Documentation/networking/phy-link-topology.rst new file mode 100644 index 000000000000..4dec5d7d6513 --- /dev/null +++ b/Documentation/networking/phy-link-topology.rst @@ -0,0 +1,121 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. _phy_link_topology: + +================= +PHY link topology +================= + +Overview +======== + +The PHY link topology representation in the networking stack aims at representing +the hardware layout for any given Ethernet link. + +An Ethernet interface from userspace's point of view is nothing but a +:c:type:`struct net_device <net_device>`, which exposes configuration options +through the legacy ioctls and the ethtool netlink commands. The base assumption +when designing these configuration APIs were that the link looks something like :: + + +-----------------------+ +----------+ +--------------+ + | Ethernet Controller / | | Ethernet | | Connector / | + | MAC | ------ | PHY | ---- | Port | ---... to LP + +-----------------------+ +----------+ +--------------+ + struct net_device struct phy_device + +Commands that needs to configure the PHY will go through the net_device.phydev +field to reach the PHY and perform the relevant configuration. + +This assumption falls apart in more complex topologies that can arise when, +for example, using SFP transceivers (although that's not the only specific case). + +Here, we have 2 basic scenarios. Either the MAC is able to output a serialized +interface, that can directly be fed to an SFP cage, such as SGMII, 1000BaseX, +10GBaseR, etc. + +The link topology then looks like this (when an SFP module is inserted) :: + + +-----+ SGMII +------------+ + | MAC | ------- | SFP Module | + +-----+ +------------+ + +Knowing that some modules embed a PHY, the actual link is more like :: + + +-----+ SGMII +--------------+ + | MAC | -------- | PHY (on SFP) | + +-----+ +--------------+ + +In this case, the SFP PHY is handled by phylib, and registered by phylink through +its SFP upstream ops. + +Now some Ethernet controllers aren't able to output a serialized interface, so +we can't directly connect them to an SFP cage. However, some PHYs can be used +as media-converters, to translate the non-serialized MAC MII interface to a +serialized MII interface fed to the SFP :: + + +-----+ RGMII +-----------------------+ SGMII +--------------+ + | MAC | ------- | PHY (media converter) | ------- | PHY (on SFP) | + +-----+ +-----------------------+ +--------------+ + +This is where the model of having a single net_device.phydev pointer shows its +limitations, as we now have 2 PHYs on the link. + +The phy_link topology framework aims at providing a way to keep track of every +PHY on the link, for use by both kernel drivers and subsystems, but also to +report the topology to userspace, allowing to target individual PHYs in configuration +commands. + +API +=== + +The :c:type:`struct phy_link_topology <phy_link_topology>` is a per-netdevice +resource, that gets initialized at netdevice creation. Once it's initialized, +it is then possible to register PHYs to the topology through : + +:c:func:`phy_link_topo_add_phy` + +Besides registering the PHY to the topology, this call will also assign a unique +index to the PHY, which can then be reported to userspace to refer to this PHY +(akin to the ifindex). This index is a u32, ranging from 1 to U32_MAX. The value +0 is reserved to indicate the PHY doesn't belong to any topology yet. + +The PHY can then be removed from the topology through + +:c:func:`phy_link_topo_del_phy` + +These function are already hooked into the phylib subsystem, so all PHYs that +are linked to a net_device through :c:func:`phy_attach_direct` will automatically +join the netdev's topology. + +PHYs that are on a SFP module will also be automatically registered IF the SFP +upstream is phylink (so, no media-converter). + +PHY drivers that can be used as SFP upstream need to call :c:func:`phy_sfp_attach_phy` +and :c:func:`phy_sfp_detach_phy`, which can be used as a +.attach_phy / .detach_phy implementation for the +:c:type:`struct sfp_upstream_ops <sfp_upstream_ops>`. + +UAPI +==== + +There exist a set of netlink commands to query the link topology from userspace, +see ``Documentation/networking/ethtool-netlink.rst``. + +The whole point of having a topology representation is to assign the phyindex +field in :c:type:`struct phy_device <phy_device>`. This index is reported to +userspace using the ``ETHTOOL_MSG_PHY_GET`` ethtnl command. Performing a DUMP operation +will result in all PHYs from all net_device being listed. The DUMP command +accepts either a ``ETHTOOL_A_HEADER_DEV_INDEX`` or ``ETHTOOL_A_HEADER_DEV_NAME`` +to be passed in the request to filter the DUMP to a single net_device. + +The retrieved index can then be passed as a request parameter using the +``ETHTOOL_A_HEADER_PHY_INDEX`` field in the following ethnl commands : + +* ``ETHTOOL_MSG_STRSET_GET`` to get the stats string set from a given PHY +* ``ETHTOOL_MSG_CABLE_TEST_ACT`` and ``ETHTOOL_MSG_CABLE_TEST_ACT``, to perform + cable testing on a given PHY on the link (most likely the outermost PHY) +* ``ETHTOOL_MSG_PSE_SET`` and ``ETHTOOL_MSG_PSE_GET`` for PHY-controlled PoE and PSE settings +* ``ETHTOOL_MSG_PLCA_GET_CFG``, ``ETHTOOL_MSG_PLCA_SET_CFG`` and ``ETHTOOL_MSG_PLCA_GET_STATUS`` + to set the PLCA (Physical Layer Collision Avoidance) parameters + +Note that the PHY index can be passed to other requests, which will silently +ignore it if present and irrelevant. |