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1.. SPDX-License-Identifier: GPL-2.02 3PSE Power Interface (PSE PI) Documentation4==========================================5 6The Power Sourcing Equipment Power Interface (PSE PI) plays a pivotal role in7the architecture of Power over Ethernet (PoE) systems. It is essentially a8blueprint that outlines how one or multiple power sources are connected to the9eight-pin modular jack, commonly known as the Ethernet RJ45 port. This10connection scheme is crucial for enabling the delivery of power alongside data11over Ethernet cables.12 13Documentation and Standards14---------------------------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 PoE20 systems that utilize two pairs for power delivery.21- Section "145.2.4 PSE PI" addresses the configuration for PoE systems that22 deliver power over all four pairs of an Ethernet cable.23 24PSE PI and Single Pair Ethernet25-------------------------------26 27Single Pair Ethernet (SPE) represents a different approach to Ethernet28connectivity, utilizing just one pair of conductors for both data and power29transmission. Unlike the configurations detailed in the PSE PI for standard30Ethernet, which can involve multiple power sourcing arrangements across four or31two pairs of wires, SPE operates on a simpler model due to its single-pair32design. As a result, the complexities of choosing between alternative pin33assignments for power delivery, as described in the PSE PI for multi-pair34Ethernet, are not applicable to SPE.35 36Understanding PSE PI37--------------------38 39The Power Sourcing Equipment Power Interface (PSE PI) is a framework defining40how Power Sourcing Equipment (PSE) delivers power to Powered Devices (PDs) over41Ethernet cables. It details two main configurations for power delivery, known42as Alternative A and Alternative B, which are distinguished not only by their43method of power transmission but also by the implications for polarity and data44transmission direction.45 46Alternative A and B Overview47----------------------------48 49- **Alternative A:** Utilizes RJ45 conductors 1, 2, 3 and 6. In either case of50 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 MDI52 (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 of56 10/100BaseT network the pairs used are spare pairs without data and are less57 influenced by data transmission direction. This is not the case for58 1G/2G/5G/10GBaseT network. Alternative B includes two configurations with59 different polarities, known as variant X and variant S, to accommodate60 different network requirements and device specifications.61 62Table 145-3 PSE Pinout Alternatives63-----------------------------------64 65The following table outlines the pin configurations for both Alternative A and66Alternative 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 that92 specific configuration.93 94PSE PI compatibilities95----------------------96 97The following table outlines the compatibility between the pinout alternative98and 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 pairs113 without using magnetics in case of spare pairs.114 - "Phantom" indicate power path over coils/magnetics as it is done for115 Alternative A variant.116 117In case of PSE 4 pairs, a PSE supporting only 10/100BaseT (which mean Direct118Power on pinout Alternative B) is not compatible with a 4 pairs1191000/2.5G/5G/10GBaseT.120 121PSE Power Interface (PSE PI) Connection Diagram122-----------------------------------------------123 124The diagram below illustrates the connection architecture between the RJ45125port, the Ethernet PHY (Physical Layer), and the PSE PI (Power Sourcing126Equipment Power Interface), demonstrating how power and data are delivered127simultaneously through an Ethernet cable. The RJ45 port serves as the physical128interface for these connections, with each of its eight pins connected to both129the 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 1141 | | | | | 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 A155---------------------------------------------156 157The diagram below illustrates a straightforward PSE PI (Power Sourcing158Equipment Power Interface) configuration designed to support the Alternative A159setup for Power over Ethernet (PoE). This implementation is tailored to provide160power delivery through the data-carrying pairs of an Ethernet cable, suitable161for either MDI or MDI-X configurations, albeit supporting one variation at a162time.163 164.. code-block::165 166 +-------------+167 | PSE PI |168 8 -----+ +-------------+169 7 -----+ Rail 1 |170 6 -----+------+----------------------+171 5 -----+ | |172 4 -----+ | Rail 2 | PSE 1173 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 in182 addition to data transmission. This aligns with the standard wiring for183 10/100BaseT Ethernet networks where these pairs are used for data.184- Rail 1 and Rail 2 represent the positive and negative voltage rails, with185 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 external187 switches to change the polarity of the voltage rails, allowing for188 compatibility with both MDI and MDI-X configurations.189 190More complex PSE PI configurations may include additional components, to support191Alternative B, or to provide additional features such as power management, or192additional 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 1204 3 -----+--------+ +----------------+205 2 -----+--------+ | |206 1 -----+--------+ | +-------------+207 | +---+208 +-------------+209 210Device Tree Configuration: Describing PSE PI Configurations211-----------------------------------------------------------212 213The necessity for a separate PSE PI node in the device tree is influenced by214the intricacy of the Power over Ethernet (PoE) system's setup. Here are215descriptions of both simple and complex PSE PI configurations to illustrate216this decision-making process:217 218**Simple PSE PI Configuration:**219In a straightforward scenario, the PSE PI setup involves a direct, one-to-one220connection between a single PSE controller and an Ethernet port. This setup221typically supports basic PoE functionality without the need for dynamic222configuration or management of multiple power delivery modes. For such simple223configurations, detailing the PSE PI within the existing PSE controller's node224may suffice, as the system does not encompass additional complexity that225warrants a separate node. The primary focus here is on the clear and direct226association 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 or230auxiliary circuits that collectively manage power delivery to one Ethernet231port. Such configurations might support a range of PoE standards and require232the capability to dynamically configure power delivery based on the operational233mode (e.g., PoE2 versus PoE4) or specific requirements of connected devices. In234these instances, a dedicated PSE PI node becomes essential for accurately235documenting the system architecture. This node would serve to detail the236interactions between different PSE controllers, the support for various PoE237modes, and any additional logic required to coordinate power delivery across238the network infrastructure.239 240**Guidance:**241 242For simple PSE setups, including PSE PI information in the PSE controller node243might 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 802.3246specifications, improving documentation clarity and ensuring accurate247representation of the PoE system's complexity.248 249PSE PI Node: Essential Information250----------------------------------251 252The PSE PI (Power Sourcing Equipment Power Interface) node in a device tree can253include several key pieces of information critical for defining the power254delivery capabilities and configurations of a PoE (Power over Ethernet) system.255Below is a list of such information, along with explanations for their256necessity 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 the261 Ethernet cable.262 - *Necessity:* Essential to ensure the correct pairs are powered according263 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 each270 powered pair.271 - *Necessity:* Critical for safe and effective power transmission to PDs.272 - *PSE Controller Node:* Polarity management may exceed the standard273 functionalities of PSE controllers.274 2753. **PSE Cells Association**276 277 - *Description:* Details the association of PSE cells with Ethernet ports or278 pairs in multi-cell configurations.279 - *Necessity:* Allows for optimized power resource allocation in complex280 systems.281 - *PSE Controller Node:* Controllers may not manage cell associations282 directly, focusing instead on power flow regulation.283 2844. **Support for PoE Standards**285 286 - *Description:* Lists the PoE standards and configurations supported by the287 system.288 - *Necessity:* Ensures system compatibility with various PDs and adherence289 to industry standards.290 - *PSE Controller Node:* Specific capabilities may depend on the overall PSE291 PI design rather than the controller alone. Multiple PSE cells per PI292 do not necessarily imply support for multiple PoE standards.293 2945. **Protection Mechanisms**295 296 - *Description:* Outlines additional protection mechanisms, such as297 overcurrent protection and thermal management.298 - *Necessity:* Provides extra safety and stability, complementing PSE299 controller protections.300 - *PSE Controller Node:* Some protections may be implemented via301 board-specific hardware or algorithms external to the controller.302