1.. SPDX-License-Identifier: GPL-2.0 2 3PSE Power Interface (PSE PI) Documentation 4========================================== 5 6The Power Sourcing Equipment Power Interface (PSE PI) plays a pivotal role in 7the architecture of Power over Ethernet (PoE) systems. It is essentially a 8blueprint that outlines how one or multiple power sources are connected to the 9eight-pin modular jack, commonly known as the Ethernet RJ45 port. This 10connection scheme is crucial for enabling the delivery of power alongside data 11over Ethernet cables. 12 13Documentation and Standards 14--------------------------- 15 16The IEEE 802.3 standard provides detailed documentation on the PSE PI. 17Specifically: 18 19- Section "33.2.3 PI pin assignments" covers the pin assignments for PoE 20 systems that utilize two pairs for power delivery. 21- Section "145.2.4 PSE PI" addresses the configuration for PoE systems that 22 deliver power over all four pairs of an Ethernet cable. 23 24PSE PI and Single Pair Ethernet 25------------------------------- 26 27Single Pair Ethernet (SPE) represents a different approach to Ethernet 28connectivity, utilizing just one pair of conductors for both data and power 29transmission. Unlike the configurations detailed in the PSE PI for standard 30Ethernet, which can involve multiple power sourcing arrangements across four or 31two pairs of wires, SPE operates on a simpler model due to its single-pair 32design. As a result, the complexities of choosing between alternative pin 33assignments for power delivery, as described in the PSE PI for multi-pair 34Ethernet, are not applicable to SPE. 35 36Understanding PSE PI 37-------------------- 38 39The Power Sourcing Equipment Power Interface (PSE PI) is a framework defining 40how Power Sourcing Equipment (PSE) delivers power to Powered Devices (PDs) over 41Ethernet cables. It details two main configurations for power delivery, known 42as Alternative A and Alternative B, which are distinguished not only by their 43method of power transmission but also by the implications for polarity and data 44transmission direction. 45 46Alternative A and B Overview 47---------------------------- 48 49- **Alternative A:** Utilizes RJ45 conductors 1, 2, 3 and 6. In either case of 50 networks 10/100BaseT or 1G/2G/5G/10GBaseT, the pairs used are carrying data. 51 The power delivery's polarity in this alternative can vary based on the MDI 52 (Medium Dependent Interface) or MDI-X (Medium Dependent Interface Crossover) 53 configuration. 54 55- **Alternative B:** Utilizes RJ45 conductors 4, 5, 7 and 8. In case of 56 10/100BaseT network the pairs used are spare pairs without data and are less 57 influenced by data transmission direction. This is not the case for 58 1G/2G/5G/10GBaseT network. Alternative B includes two configurations with 59 different polarities, known as variant X and variant S, to accommodate 60 different network requirements and device specifications. 61 62Table 145-3 PSE Pinout Alternatives 63----------------------------------- 64 65The following table outlines the pin configurations for both Alternative A and 66Alternative B. 67 68+------------+-------------------+-----------------+-----------------+-----------------+ 69| Conductor | Alternative A | Alternative A | Alternative B | Alternative B | 70| | (MDI-X) | (MDI) | (X) | (S) | 71+============+===================+=================+=================+=================+ 72| 1 | Negative V | Positive V | - | - | 73+------------+-------------------+-----------------+-----------------+-----------------+ 74| 2 | Negative V | Positive V | - | - | 75+------------+-------------------+-----------------+-----------------+-----------------+ 76| 3 | Positive V | Negative V | - | - | 77+------------+-------------------+-----------------+-----------------+-----------------+ 78| 4 | - | - | Negative V | Positive V | 79+------------+-------------------+-----------------+-----------------+-----------------+ 80| 5 | - | - | Negative V | Positive V | 81+------------+-------------------+-----------------+-----------------+-----------------+ 82| 6 | Positive V | Negative V | - | - | 83+------------+-------------------+-----------------+-----------------+-----------------+ 84| 7 | - | - | Positive V | Negative V | 85+------------+-------------------+-----------------+-----------------+-----------------+ 86| 8 | - | - | Positive V | Negative V | 87+------------+-------------------+-----------------+-----------------+-----------------+ 88 89.. note:: 90 - "Positive V" and "Negative V" indicate the voltage polarity for each pin. 91 - "-" indicates that the pin is not used for power delivery in that 92 specific configuration. 93 94PSE PI compatibilities 95---------------------- 96 97The following table outlines the compatibility between the pinout alternative 98and the 1000/2.5G/5G/10GBaseT in the PSE 2 pairs connection. 99 100+---------+---------------+---------------------+-----------------------+ 101| Variant | Alternative | Power Feeding Type | Compatibility with | 102| | (A/B) | (Direct/Phantom) | 1000/2.5G/5G/10GBaseT | 103+=========+===============+=====================+=======================+ 104| 1 | A | Phantom | Yes | 105+---------+---------------+---------------------+-----------------------+ 106| 2 | B | Phantom | Yes | 107+---------+---------------+---------------------+-----------------------+ 108| 3 | B | Direct | No | 109+---------+---------------+---------------------+-----------------------+ 110 111.. note:: 112 - "Direct" indicate a variant where the power is injected directly to pairs 113 without using magnetics in case of spare pairs. 114 - "Phantom" indicate power path over coils/magnetics as it is done for 115 Alternative A variant. 116 117In case of PSE 4 pairs, a PSE supporting only 10/100BaseT (which mean Direct 118Power on pinout Alternative B) is not compatible with a 4 pairs 1191000/2.5G/5G/10GBaseT. 120 121PSE Power Interface (PSE PI) Connection Diagram 122----------------------------------------------- 123 124The diagram below illustrates the connection architecture between the RJ45 125port, the Ethernet PHY (Physical Layer), and the PSE PI (Power Sourcing 126Equipment Power Interface), demonstrating how power and data are delivered 127simultaneously through an Ethernet cable. The RJ45 port serves as the physical 128interface for these connections, with each of its eight pins connected to both 129the Ethernet PHY for data transmission and the PSE PI for power delivery. 130 131.. code-block:: 132 133 +--------------------------+ 134 | | 135 | RJ45 Port | 136 | | 137 +--+--+--+--+--+--+--+--+--+ +-------------+ 138 1| 2| 3| 4| 5| 6| 7| 8| | | 139 | | | | | | | o-------------------+ | 140 | | | | | | o--|-------------------+ +<--- PSE 1 141 | | | | | o--|--|-------------------+ | 142 | | | | o--|--|--|-------------------+ | 143 | | | o--|--|--|--|-------------------+ PSE PI | 144 | | o--|--|--|--|--|-------------------+ | 145 | o--|--|--|--|--|--|-------------------+ +<--- PSE 2 (optional) 146 o--|--|--|--|--|--|--|-------------------+ | 147 | | | | | | | | | | 148 +--+--+--+--+--+--+--+--+--+ +-------------+ 149 | | 150 | Ethernet PHY | 151 | | 152 +--------------------------+ 153 154Simple PSE PI Configuration for Alternative A 155--------------------------------------------- 156 157The diagram below illustrates a straightforward PSE PI (Power Sourcing 158Equipment Power Interface) configuration designed to support the Alternative A 159setup for Power over Ethernet (PoE). This implementation is tailored to provide 160power delivery through the data-carrying pairs of an Ethernet cable, suitable 161for either MDI or MDI-X configurations, albeit supporting one variation at a 162time. 163 164.. code-block:: 165 166 +-------------+ 167 | PSE PI | 168 8 -----+ +-------------+ 169 7 -----+ Rail 1 | 170 6 -----+------+----------------------+ 171 5 -----+ | | 172 4 -----+ | Rail 2 | PSE 1 173 3 -----+------/ +------------+ 174 2 -----+--+-------------/ | 175 1 -----+--/ +-------------+ 176 | 177 +-------------+ 178 179In this configuration: 180 181- Pins 1 and 2, as well as pins 3 and 6, are utilized for power delivery in 182 addition to data transmission. This aligns with the standard wiring for 183 10/100BaseT Ethernet networks where these pairs are used for data. 184- Rail 1 and Rail 2 represent the positive and negative voltage rails, with 185 Rail 1 connected to pins 1 and 2, and Rail 2 connected to pins 3 and 6. 186 More advanced PSE PI configurations may include integrated or external 187 switches to change the polarity of the voltage rails, allowing for 188 compatibility with both MDI and MDI-X configurations. 189 190More complex PSE PI configurations may include additional components, to support 191Alternative B, or to provide additional features such as power management, or 192additional power delivery capabilities such as 2-pair or 4-pair power delivery. 193 194.. code-block:: 195 196 +-------------+ 197 | PSE PI | 198 | +---+ 199 8 -----+--------+ | +-------------+ 200 7 -----+--------+ | Rail 1 | 201 6 -----+--------+ +-----------------+ 202 5 -----+--------+ | | 203 4 -----+--------+ | Rail 2 | PSE 1 204 3 -----+--------+ +----------------+ 205 2 -----+--------+ | | 206 1 -----+--------+ | +-------------+ 207 | +---+ 208 +-------------+ 209 210Device Tree Configuration: Describing PSE PI Configurations 211----------------------------------------------------------- 212 213The necessity for a separate PSE PI node in the device tree is influenced by 214the intricacy of the Power over Ethernet (PoE) system's setup. Here are 215descriptions of both simple and complex PSE PI configurations to illustrate 216this decision-making process: 217 218**Simple PSE PI Configuration:** 219In a straightforward scenario, the PSE PI setup involves a direct, one-to-one 220connection between a single PSE controller and an Ethernet port. This setup 221typically supports basic PoE functionality without the need for dynamic 222configuration or management of multiple power delivery modes. For such simple 223configurations, detailing the PSE PI within the existing PSE controller's node 224may suffice, as the system does not encompass additional complexity that 225warrants a separate node. The primary focus here is on the clear and direct 226association of power delivery to a specific Ethernet port. 227 228**Complex PSE PI Configuration:** 229Contrastingly, a complex PSE PI setup may encompass multiple PSE controllers or 230auxiliary circuits that collectively manage power delivery to one Ethernet 231port. Such configurations might support a range of PoE standards and require 232the capability to dynamically configure power delivery based on the operational 233mode (e.g., PoE2 versus PoE4) or specific requirements of connected devices. In 234these instances, a dedicated PSE PI node becomes essential for accurately 235documenting the system architecture. This node would serve to detail the 236interactions between different PSE controllers, the support for various PoE 237modes, and any additional logic required to coordinate power delivery across 238the network infrastructure. 239 240**Guidance:** 241 242For simple PSE setups, including PSE PI information in the PSE controller node 243might suffice due to the straightforward nature of these systems. However, 244complex configurations, involving multiple components or advanced PoE features, 245benefit from a dedicated PSE PI node. This method adheres to IEEE 802.3 246specifications, improving documentation clarity and ensuring accurate 247representation of the PoE system's complexity. 248 249PSE PI Node: Essential Information 250---------------------------------- 251 252The PSE PI (Power Sourcing Equipment Power Interface) node in a device tree can 253include several key pieces of information critical for defining the power 254delivery capabilities and configurations of a PoE (Power over Ethernet) system. 255Below is a list of such information, along with explanations for their 256necessity and reasons why they might not be found within a PSE controller node: 257 2581. **Powered Pairs Configuration** 259 260 - *Description:* Identifies the pairs used for power delivery in the 261 Ethernet cable. 262 - *Necessity:* Essential to ensure the correct pairs are powered according 263 to the board's design. 264 - *PSE Controller Node:* Typically lacks details on physical pair usage, 265 focusing on power regulation. 266 2672. **Polarity of Powered Pairs** 268 269 - *Description:* Specifies the polarity (positive or negative) for each 270 powered pair. 271 - *Necessity:* Critical for safe and effective power transmission to PDs. 272 - *PSE Controller Node:* Polarity management may exceed the standard 273 functionalities of PSE controllers. 274 2753. **PSE Cells Association** 276 277 - *Description:* Details the association of PSE cells with Ethernet ports or 278 pairs in multi-cell configurations. 279 - *Necessity:* Allows for optimized power resource allocation in complex 280 systems. 281 - *PSE Controller Node:* Controllers may not manage cell associations 282 directly, focusing instead on power flow regulation. 283 2844. **Support for PoE Standards** 285 286 - *Description:* Lists the PoE standards and configurations supported by the 287 system. 288 - *Necessity:* Ensures system compatibility with various PDs and adherence 289 to industry standards. 290 - *PSE Controller Node:* Specific capabilities may depend on the overall PSE 291 PI design rather than the controller alone. Multiple PSE cells per PI 292 do not necessarily imply support for multiple PoE standards. 293 2945. **Protection Mechanisms** 295 296 - *Description:* Outlines additional protection mechanisms, such as 297 overcurrent protection and thermal management. 298 - *Necessity:* Provides extra safety and stability, complementing PSE 299 controller protections. 300 - *PSE Controller Node:* Some protections may be implemented via 301 board-specific hardware or algorithms external to the controller. 302