netdev - RE: [v2 1/2] Docs/devicetree: add serdes-output-amplitude-mv to marvell.txt

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Date:   Mon, 6 Dec 2021 16:44:58 +0000
From:   Holger Brunck <holger.brunck@...achienergy.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Marek Behún <kabel@...nel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>
Subject: RE: [v2 1/2] Docs/devicetree: add serdes-output-amplitude-mv to
 marvell.txt

> > > diff --git a/Documentation/devicetree/bindings/net/dsa/marvell.txt
> > > b/Documentation/devicetree/bindings/net/dsa/marvell.txt
> > > index 2363b412410c..9292b6f960df 100644
> > > --- a/Documentation/devicetree/bindings/net/dsa/marvell.txt
> > > +++ b/Documentation/devicetree/bindings/net/dsa/marvell.txt
> > > @@ -46,6 +46,11 @@ Optional properties:
> > >  - mdio?            : Container of PHYs and devices on the external MDIO
> > >                       bus. The node must contains a compatible string of
> > >                       "marvell,mv88e6xxx-mdio-external"
> > > +- serdes-output-amplitude-mv: Configure the output amplitude of the
> serdes
> > > +                         interface in millivolts. This option can be
> > > +                              set in the ports node as it is a property of
> > > +                              the port.
> > > +    serdes-output-amplitude-mv = <210>;
> >
> > The suffix should be millivolt, as can be seen in other bindings.
> 
> My bad. I recommended that. It does seem like both are used, but millivolt is
> more popular.
> 
> > Also I think maybe use "tx" instead of "output"? It is more common to
> > refere to serdes pairs as rx/tx instead of input/output:
> >
> >   serdes-tx-amplitude-millivolt
> >
> > I will probably want to add this property also either to mvneta, or to
> > A3720 common PHY binding. Andrew, do you think it should be put
> > somewhere more generic?
> 
> Not sure what the common location would be. I assume for mvneta and
> A3720 it is part of the generic phy comphy driver? Does generic phy have any
> properties like this already?
> 
> Here we are using it in DSA. And it could also be used in a Marvell phy driver
> node.
> 
> So maybe something like serdes.yaml?
> bindings/phy/microchip,sparx5-serdes.yaml actually mentions
> 
>   * Tx output amplitude control
> 
> but does not define a property for it, but that looks like another use case for it.
> 

so what is the conclusion here? Should I add it to marvell.txt for now or is there
a better place?

Best regards
Holger