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

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Message-ID: <20231121110215.07f61e55@kmaincent-XPS-13-7390>
Date:   Tue, 21 Nov 2023 11:02:15 +0100
From:   Köry Maincent <kory.maincent@...tlin.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        "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

On Mon, 20 Nov 2023 19:00:03 +0100
Andrew Lunn <andrew@...n.ch> wrote:

> > 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?

If we decide to add a prefix, "c33" is precise but less easily understandable,
why not using simply "poe" prefix?
Maybe as POE were originally PMDI you prefer to use c33 which won't change over
time? 

Should I also modify the content of the enum?
ETHTOOL_PSE_ADMIN_STATE_* to ETHTOOL_C33_PSE_ADMIN_*
ETHTOOL_PSE_PW_D_STATUS_* to ETHTOOL_C33_PSE_PW_D_STATUS_*


-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com