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Date: Sat, 17 Feb 2024 07:46:49 +0100 From: Oleksij Rempel <o.rempel@...gutronix.de> To: Andrew Lunn <andrew@...n.ch> Cc: Rob Herring <robh@...nel.org>, Kory 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>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, Mark Brown <broonie@...nel.org>, Frank Rowand <frowand.list@...il.com>, Heiner Kallweit <hkallweit1@...il.com>, Russell King <linux@...linux.org.uk>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, devicetree@...r.kernel.org, Dent Project <dentproject@...uxfoundation.org> Subject: Re: [PATCH net-next v3 14/17] dt-bindings: net: pse-pd: Add bindings for PD692x0 PSE controller Hi Kory, Can you please integrated this new insights to the PSE PI documentation. Instead of 1000BaseT only, please use 1000/2.5G/5G/10GBASE-T as documented in the spec. On Fri, Feb 16, 2024 at 08:47:14AM +0100, Oleksij Rempel wrote: > On Thu, Feb 15, 2024 at 06:51:55PM +0100, Andrew Lunn wrote: > > > Hm.. good question. I didn't found the answer in the spec. By combining all > > > puzzle parts I assume, different Alternative configurations are designed > > > to handle conflict between "PSE Physical Layer classification" and PHY > > > autoneg. > > > > > > Here is how multi-pulse Physical Layer classification is done: > > > https://img.electronicdesign.com/files/base/ebm/electronicdesign/image/2020/07/Figure_5.5f2094553a61c.png > > > > > > this is the source: > > > https://www.electronicdesign.com/technologies/power/whitepaper/21137799/silicon-labs-90-w-power-over-ethernet-explained > > > > > > To avoid classification conflict with autoneg. Assuming, PHY on PD side > > > will be not powered until classification is completed. The only source > > > of pulses is the PHY on PSE side (if it is not under control of software > > > on PSE side or Midspan PSE is used), so aneg pulses should be send on > > > negative PoE pair? This all is just speculation, I would need to ask > > > some expert or do testing. > > > > > > If this assumption is correct, PHY framework will need to know exact > > > layout of MDI-X setting and/or silent PHY until PSE classification is done. > > > > Ideally, we don't want to define a DT binding, and then find it is > > wrong for 1000BaseT and above and we need to change it. > > > > So, either somebody needs to understand 1000BaseT and can say the > > proposed binding works, or we explicitly document the binding is > > limited to 10BaseT and 100BaseT. > > I asked the internet and found the answer: Some PSE/PD implementations > are not compatible with 1000BaseT. > > See Figure 33–4—10BASE-T/100BASE-TX Endpoint PSE location overview. > Alternative B show a variant where power is injected directly to pairs > without using magnetics as it is done for Alternative A (phantom > delivery - over magnetics). > > I assume, the reasoning for this kind of design is simple - price. > Otherwise magnetics will have special requirements: > https://www.coilcraft.com/de-de/edu/series/magnetics-for-power-over-ethernet/ > > So, we have following variants of 2 pairs PoE: > +---------+---------------+-------------------+---------------------+--------------------+ > | Variant | Alternative | Polarity | Power Feeding Type | Compatibility with | > | | (a/b) | (Direct/Reverse) | (Direct/Phantom) | 1000BaseT | > +=========+===============+===================+=====================+====================+ > | 1 | a | Direct | Phantom | Yes | > +---------+---------------+-------------------+---------------------+--------------------+ > | 2 | a | Reverse | Phantom | Yes | > +---------+---------------+-------------------+---------------------+--------------------+ > | 3 | b | Direct | Phantom | Yes | > +---------+---------------+-------------------+---------------------+--------------------+ > | 4 | b | Reverse | Phantom | Yes | > +---------+---------------+-------------------+---------------------+--------------------+ > | 5 | b | Direct | Direct | No | > +---------+---------------+-------------------+---------------------+--------------------+ > | 6 | b | Reverse | Direct | No | > +---------+---------------+-------------------+---------------------+--------------------+ > > An advanced PSE may implement range of different variants direct in the PSE > controller or with additional ICs in the PSE PI. The same is about PD. > > Let's take as example PD-IM-7608M eval board: > https://www.microchip.com/en-us/development-tool/PD-IM-7608M > > According to the schematics: > https://ww1.microchip.com/downloads/en/DeviceDoc/PD-IM-7608M.zip > It supports only Variant 5 - Alternative B, with only one polarity, > and direct feeding without magnetics. > > The simple PD may support only one variant: > https://community.fs.com/article/troubleshooting-poe-errors.html > " the power modes of PSE and PD are other factors that may cause PoE > faults. There are three PoE modes: Alternative A, alternative B, and > 4-pair delivery. If a PD only supports PoE mode B power delivery, while > a PoE switch is based on Alternative A, as a result, the PD and PoE > switch can not work together." > > For this case, it will be good if systems knows supported modes, so user > can get this information directly. For example with ethtool > > -- > Pengutronix e.K. | | > Steuerwalder Str. 21 | http://www.pengutronix.de/ | > 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | > Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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