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

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Message-ID: <20240705-curing-lisp-c10eccf74685@spud>
Date: Fri, 5 Jul 2024 15:51:06 +0100
From: Conor Dooley <conor@...nel.org>
To: Andrew Lunn <andrew@...n.ch>
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

On Thu, Jul 04, 2024 at 11:11:41PM +0200, Andrew Lunn wrote:
> > > ---
> > >  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

nit: an alternative

> > > +      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.

Right, I guess for people that want brr-mode they'll probably understand
that and it's just unclear to me as I don't :) The nitpicking side of my
brain would like that last sentence reworded to "The PHY must be
configured to operate in BroadR-Reach mode by software", mostly cos the
word "driver" assumes a particular model for the OS, but it's not really
a big deal.

Acked-by: Conor Dooley <conor.dooley@...rochip.com>

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