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Linux 6.18.37 · Networking

PHY 링크 토폴로지

다중 PHY Ethernet 링크를 커널과 사용자 공간에서 추적하고 개별 phyindex로 구성하는 토폴로지 모델입니다.

Source pathDocumentation/networking/phy-link-topology.rst
Source versionLinux v6.18.37
TranslationDUJINLABS 전문 번역 + 해설

요약·해설과 원문, 전문 번역을 서로 분리했습니다. API 이름, symbol, source path는 원문 표기를 사용합니다.

1. 요약·해설

원문의 핵심 논리와 kernel programming 관점의 보충 설명입니다. 아래의 전문 번역과는 별도로 작성했습니다.

2. 영어 원문 전체

번역 기준이 된 Linux v6.18.37 원문입니다. 줄 번호는 이 버전의 파일 좌표입니다.

원문 전체 펼치기
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.
122

3. 한국어 전문 번역

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