linux-kernel - Re: [PATCH net-next 2/9] ethtool: Expand Ethernet Power Equipment with PoE alongside PoDL

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Message-ID: <2539b109-72ad-470a-9dae-9f53de4f64ec@lunn.ch>
Date:   Mon, 20 Nov 2023 19:00:03 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Köry Maincent <kory.maincent@...tlin.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Russ Weight <russ.weight@...ux.dev>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next 2/9] ethtool: Expand Ethernet Power Equipment
 with PoE alongside PoDL

> > > >  struct pse_control_config {
> > > >  	enum ethtool_podl_pse_admin_state podl_admin_control;
> > > > +	enum ethtool_pse_admin_state admin_control;  
> > > 
> > > When i look at this, it seems to me admin_control should be generic
> > > across all schemes which put power down the cable, and
> > > podl_admin_control is specific to how PoDL puts power down the cable.
> > >
> > > Since you appear to be adding support for a second way to put power
> > > down the cable, i would expect something like poe_admin_control being
> > > added here. But maybe that is in a later patch?
> > 
> > No as said above admin_control is for PoE and podl_admin_control is for PoDL.
> > Maybe you prefer to use poe_admin_control, and add poe prefix in the poe
> > variables. It will differ a bit from the IEEE standard naming but I agreed that
> > it would be more understandable in the development part.
> 
> Official name for "PoE" is "Power via Media Dependent Interface". PoE is
> not used in the IEEE 802.3-2018. Using names not used in the specification,
> make development even harder :)
> Especially since there are even more marketing names (names not used in the
> specification) for different PoE variants:
> - 802.3af (802.3at Type 1), PoE
> - 802.3at Type 2, PoE+
> - 802.3bt Type 3, 4PPoE or PoE++
> - 802.3bt Type 4, 4PPoE or PoE++

>From the 2018 standard:

  1.4.407 Power Sourcing Equipment (PSE): A DTE or midspan device that
  provides the power to a single link section. PSEs are defined for
  use with two different types of balanced twisted-pair PHYs. When
  used with 2 or 4 pair balanced twisted-pair (BASE-T) PHYs, (see IEEE
  Std 802.3, Clause 33), DTE powering is intended to provide a single
  10BASE-T, 100BASE-TX, or 1000BASE-T device with a unified interface
  for both the data it requires and the power to process these
  data. When used with single balanced twisted-pair (BASE-T1) PHYs
  (see IEEE Std 802.3, Clause 104), DTE powering is intended to
  provide a single 100BASE-T1 or 1000BASE-T1 device with a unified
  interface for both the data it requires and the power to process
  these data. A PSE used with balanced single twisted-pair PHYs is
  also referred to as a PoDL PSE.

So it seems like, anything not PoDL PSE does not have a name :-(

However, everything not PoDL PSE seems to be clause 33. So how about:

	enum ethtool_podl_pse_admin_state podl_admin_control;
	enum ethtool_c33_pse_admin_state c33_admin_control;  

At least inside the kernel we use c22, c45, c37 etc. I'm not sure they
are visible to userspace, but if we don't have a better name, maybe we
have to use c33 in userspace as well.

I do think naming like this makes it clear we are talking about two
parallel technologies, not a generic layer and then extensions for
podl.

What do you think?

	Andrew