netdev - Re: [PATCH v10 3/4] dt-bindings: ethernet-phy: add optional brr-mode flag

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Message-ID: <35d571bd-251d-45b5-9e4f-93c83d1a43c8@lunn.ch>
Date: Thu, 4 Jul 2024 23:11:41 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Conor Dooley <conor@...nel.org>
Cc: Kamil Horák (2N) <kamilh@...s.com>,
	florian.fainelli@...adcom.com,
	bcm-kernel-feedback-list@...adcom.com, hkallweit1@...il.com,
	linux@...linux.org.uk, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, robh@...nel.org,
	krzk+dt@...nel.org, conor+dt@...nel.org, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 3/4] dt-bindings: ethernet-phy: add optional brr-mode
 flag

> > ---
> >  Documentation/devicetree/bindings/net/ethernet-phy.yaml | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/net/ethernet-phy.yaml b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > index 8fb2a6ee7e5b..349ae72ebf42 100644
> > --- a/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > +++ b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > @@ -93,6 +93,14 @@ properties:
> >        the turn around line low at end of the control phase of the
> >        MDIO transaction.
> >  
> > +  brr-mode:
> > +    $ref: /schemas/types.yaml#/definitions/flag
> > +    description:
> > +      If set, indicates the network cable interface is alternative one as
> > +      defined in the BroadR-Reach link mode specification under 1BR-100 and
> > +      1BR-10 names. The driver needs to configure the PHY to operate in
> > +      BroadR-Reach mode.
> 
> I find this second sentence unclear. Does the driver need to do
> configure the phy because this mode is not enabled by default or because
> the device will not work outside of this mode.

BroadR-Reach uses one pair. Standard 10/100Mbps ethernet needs 2 pair,
and 1G needs 4 pair. So any attempt to use standard 10/100/1G is going
to fail, the socket/plug and cable just don't work for anything other
than BroadR-Reach.

As far as i understand it, the PHY could be strapped into BroadR-Reach
mode, but there is no guarantee it is, so we should also program it to
BroadR-Reach mode if this property is present.

	Andrew