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Date:   Sun, 3 Dec 2023 19:27:48 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     Kory Maincent <kory.maincent@bootlin.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Russ Weight <russ.weight@linux.dev>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Oleksij Rempel <o.rempel@pengutronix.de>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, devicetree@vger.kernel.org,
        Dent Project <dentproject@linuxfoundation.org>
Subject: Re: [PATCH net-next v2 2/8] ethtool: Expand Ethernet Power Equipment
 with c33 (PoE) alongside PoDL
Message-ID: <44c873f6-66fa-48bb-bc51-9ef20a772cea@lunn.ch>
References: <20231201-feature_poe-v2-0-56d8cac607fa@bootlin.com>
 <20231201-feature_poe-v2-2-56d8cac607fa@bootlin.com>
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> +++ b/Documentation/networking/pse-pd/introduction.rst
> @@ -0,0 +1,73 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +Power Sourcing Equipment (PSE) in IEEE 802.3 Standard
> +=====================================================
> +
> +Overview
> +--------
> +
> +Power Sourcing Equipment (PSE) is essential in networks for delivering power
> +along with data over Ethernet cables. It usually refers to devices like
> +switches and hubs that supply power to Powered Devices (PDs) such as IP
> +cameras, VoIP phones, and wireless access points.
> +
> +PSE vs. PoDL PSE
> +----------------
> +
> +PSE in the IEEE 802.3 standard generally refers to equipment that provides
> +power alongside data over Ethernet cables, typically associated with Power over
> +Ethernet (PoE).
> +
> +PoDL PSE, or Power over Data Lines PSE, specifically denotes PSEs operating
> +with single balanced twisted-pair PHYs, as per Clause 104 of IEEE 802.3. PoDL
> +is significant in contexts like automotive and industrial controls where power
> +and data delivery over a single pair is advantageous.
> +
> +IEEE 802.3-2018 Addendums and Related Clauses
> +----------------------------------------------
> +
> +Key addenda to the IEEE 802.3-2018 standard relevant to power delivery over
> +Ethernet are as follows:
> +
> +- **802.3af (Approved in 2003-06-12)**: Known as PoE in the market, detailed in
> +  Clause 33, delivering up to 15.4W of power.
> +- **802.3at (Approved in 2009-09-11)**: Marketed as PoE+, enhancing PoE as
> +  covered in Clause 33, increasing power delivery to up to 30W.
> +- **802.3bt (Approved in 2018-09-27)**: Known as 4PPoE in the market, outlined
> +  in Clause 33. Type 3 delivers up to 60W, and Type 4 up to 100W.
> +- **802.3bu (Approved in 2016-12-07)**: Formerly referred to as PoDL, detailed
> +  in Clause 104. Introduces Classes 0 - 9. Class 9 PoDL PSE delivers up to ~65W
> +
> +Kernel Naming Convention Recommendations
> +----------------------------------------
> +
> +For clarity and consistency within the Linux kernel's networking subsystem, the
> +following naming conventions are recommended:
> +
> +- For general PSE (PoE) code, use "c33_pse" key words. For example:
> +  ``enum ethtool_c33_pse_admin_state c33_admin_control;``.
> +  This aligns with Clause 33, encompassing various PoE forms.
> +
> +- For PoDL PSE - specific code, use "podl_pse". For example:
> +  ``enum ethtool_podl_pse_admin_state podl_admin_control;`` to differentiate
> +  PoDL PSE settings according to Clause 104.
> +
> +Summary of Clause 33: Data Terminal Equipment (DTE) Power via Media Dependent Interface (MDI)
> +-------------------------------------------------------------------------------------------
> +
> +Clause 33 of the IEEE 802.3 standard defines the functional and electrical
> +characteristics of Powered Device (PD) and Power Sourcing Equipment (PSE).
> +These entities enable power delivery using the same generic cabling as for data
> +transmission, integrating power with data communication for devices such as
> +10BASE-T, 100BASE-TX, or 1000BASE-T.
> +
> +Summary of Clause 104: Power over Data Lines (PoDL) of Single Balanced Twisted-Pair Ethernet
> +-------------------------------------------------------------------------------------------
> +
> +Clause 104 of the IEEE 802.3 standard delineates the functional and electrical
> +characteristics of PoDL Powered Devices (PDs) and PoDL Power Sourcing Equipment
> +(PSEs). These are designed for use with single balanced twisted-pair Ethernet
> +Physical Layers. In this clause, 'PSE' refers specifically to PoDL PSE, and
> +'PD' to PoDL PD. The key intent is to provide devices with a unified interface
> +for both data and the power required to process this data over a single
> +balanced twisted-pair Ethernet connection.

This is a nice summary of the different standard and naming. Thanks
for adding this.

The c33 prefix is not ideal in terms of 'marketing', but we now have a
clear structure for how these two different schemes are
same/different.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew