ethtool: Expand Ethernet Power Equipment with c33 (PoE) alongside PoDL

In the current PSE interface for Ethernet Power Equipment, support is
limited to PoDL. This patch extends the interface to accommodate the
objects specified in IEEE 802.3-2022 145.2 for Power sourcing
Equipment (PSE).

The following objects are now supported and considered mandatory:
- IEEE 802.3-2022 30.9.1.1.5 aPSEPowerDetectionStatus
- IEEE 802.3-2022 30.9.1.1.2 aPSEAdminState
- IEEE 802.3-2022 30.9.1.2.1 aPSEAdminControl

To avoid confusion between "PoDL PSE" and "PoE PSE", which have similar
names but distinct values, we have followed the suggestion of Oleksij
Rempel and Andrew Lunn to maintain separate naming schemes for each,
using c33 (clause 33) prefix for "PoE PSE".
You can find more details in the discussion threads here:
https://lore.kernel.org/netdev/20230912110637.GI780075@pengutronix.de/
https://lore.kernel.org/netdev/2539b109-72ad-470a-9dae-9f53de4f64ec@lunn.ch/

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Link: https://lore.kernel.org/r/20240417-feature_poe-v9-1-242293fd1900@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 83 insertions, 0 deletions

diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst
index 473d72c36d61..7664c0bfe461 100644
--- a/Documentation/networking/index.rst
+++ b/Documentation/networking/index.rst
@@ -93,6 +93,7 @@ Contents:
    plip
    ppp_generic
    proc_net_tcp
+   pse-pd/index
    radiotap-headers
    rds
    regulatory
diff --git a/Documentation/networking/pse-pd/index.rst b/Documentation/networking/pse-pd/index.rst
new file mode 100644
index 000000000000..18197bc7303d
--- /dev/null
+++ b/Documentation/networking/pse-pd/index.rst
@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Power Sourcing Equipment (PSE) Documentation
+============================================
+
+.. toctree::
+   :maxdepth: 2
+
+   introduction
diff --git a/Documentation/networking/pse-pd/introduction.rst b/Documentation/networking/pse-pd/introduction.rst
new file mode 100644
index 000000000000..e3d3faaef717
--- /dev/null
+++ 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.