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

[Oleksij Rempel <o.rempel@pengutronix.de>]

On Fri, Sep 06, 2024 at 05:11:54PM +0200, Andrew Lunn wrote:
> 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@pengutronix.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.

Yes, at this point i was uncertain.

> What you are effectively adding is support for the ethtool:
> 
> ethtool -s [master-slave preferred-master|preferred-slave|forced-master|forced-slave]

ack

> 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.

Good point.

> 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?

Yes, this is the idea.

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