linux-kernel - Re: [PATCH v1] dt-bindings: net: ethernet-phy: Add forced-master/slave properties for SPE PHYs

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Message-ID: <c08ac9b7-08e1-4cde-979c-ed66d4a252f1@lunn.ch>
Date: Fri, 6 Sep 2024 17:11:54 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Florian Fainelli <f.fainelli@...il.com>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Russell King <linux@...linux.org.uk>, devicetree@...r.kernel.org
Subject: Re: [PATCH v1] dt-bindings: net: ethernet-phy: Add
 forced-master/slave properties for SPE PHYs

On Fri, Sep 06, 2024 at 04:49:05PM +0200, Oleksij Rempel wrote:
> Add two new properties, `forced-master` and `forced-slave`, to the
> ethernet-phy binding. These properties are intended for Single Pair
> Ethernet (1000/100/10Base-T1) PHYs, where each PHY and product may have
> a predefined link role (master or slave). Typically, these roles are set
> by hardware strap pins, but in some cases, device tree configuration is
> necessary.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> ---
>  .../devicetree/bindings/net/ethernet-phy.yaml | 22 +++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/net/ethernet-phy.yaml b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> index d9b62741a2259..af7a1eb6ceff6 100644
> --- a/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> +++ b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> @@ -158,6 +158,28 @@ properties:
>        Mark the corresponding energy efficient ethernet mode as
>        broken and request the ethernet to stop advertising it.
> 
> +  forced-master:
> +    $ref: /schemas/types.yaml#/definitions/flag
> +    description:
> +      If set, forces the PHY to operate as a master. This is used in Single Pair
> +      Ethernet (1000/100/10Base-T1) where each PHY and product has a predefined
> +      link role (master or slave). This property is board-specific, as the role
> +      is usually configured by strap pins but can be set through the device tree
> +      if needed.
> +      This property is mutually exclusive with 'forced-slave'; only one of them
> +      should be used.

DT reviewers tend to complain about such mutually exclusive
properties.

What you are effectively adding is support for the ethtool:

ethtool -s [master-slave preferred-master|preferred-slave|forced-master|forced-slave]

10Base-T1 often does not have autoneg, so preferred-master &
preferred-slave make non sense in this context, but i wounder if
somebody will want these later. An Ethernet switch is generally
preferred-master for example, but the client is preferred-slave.

Maybe make the property a string with supported values 'forced-master'
and 'forced-slave', leaving it open for the other two to be added
later.

I've not seen the implementation yet, but i don't think there is much
driver specific here. We already have phydev->master_slave_set, it
just needs to be set from this property. Can it be done in phylib core
somewhere?

	Andrew