netdev - Re: [PATCH devicetree v3] dt-bindings: phy: Add `tx-p2p-microvolt` property binding

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Date:   Thu, 20 Jan 2022 09:49:14 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Marek Behún <kabel@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Vladimir Oltean <olteanv@...il.com>,
        Holger Brunck <holger.brunck@...achienergy.com>,
        Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        linux-phy@...ts.infradead.org, Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...com>, ore@...gutronix.de,
        alexandru.tachici@...log.com
Subject: Re: [PATCH devicetree v3] dt-bindings: phy: Add `tx-p2p-microvolt`
 property binding

On 19.01.2022 14:11:17, Marek Behún wrote:
> Common PHYs and network PCSes often have the possibility to specify
> peak-to-peak voltage on the differential pair - the default voltage
> sometimes needs to be changed for a particular board.
> 
> Add properties `tx-p2p-microvolt` and `tx-p2p-microvolt-names` for this
> purpose. The second property is needed to specify the mode for the
> corresponding voltage in the `tx-p2p-microvolt` property, if the voltage
> is to be used only for speficic mode. More voltage-mode pairs can be
> specified.
> 
> Example usage with only one voltage (it will be used for all supported
> PHY modes, the `tx-p2p-microvolt-names` property is not needed in this
> case):
> 
>   tx-p2p-microvolt = <915000>;
> 
> Example usage with voltages for multiple modes:
> 
>   tx-p2p-microvolt = <915000>, <1100000>, <1200000>;
>   tx-p2p-microvolt-names = "2500base-x", "usb", "pcie";
> 
> Add these properties into a separate file phy/transmit-amplitude.yaml,
> which should be referenced by any binding that uses it.

If I understand your use-case correctly, you need different voltage p2p
levels in the connection between the Ethernet MAC and the Ethernet
switch or Ethernet-PHY?

Some of the two wire Ethernet standards (10base-T1S, 10base-T1L,
100base-T1, 1000base-T1) defines several p2p voltage levels on the wire,
i.e. between the PHYs. Alexandru has posed a series where you can
specify the between-PHY voltage levels:

| https://lore.kernel.org/all/20211210110509.20970-8-alexandru.tachici@analog.com/

Can we make clear that your binding specifies the voltage level on the
MII interface, in contrast Alexandru's binding?

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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