linux-kernel - Re: [PATCH v2 2/3] dt-bindings: net: phy: Document support for external PHY clk

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Date:   Fri, 02 Jun 2023 15:26:53 -0400
From:   Detlev Casanova <detlev.casanova@...labora.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     linux-kernel@...r.kernel.org,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 2/3] dt-bindings: net: phy: Document support for external PHY
 clk

On Friday, June 2, 2023 2:42:38 P.M. EDT Andrew Lunn wrote:
> On Fri, Jun 02, 2023 at 02:26:58PM -0400, Detlev Casanova wrote:
> > Ethern PHYs can have external an clock that needs to be activated before
> > probing the PHY.
> 
> `Ethernet PHYs can have an external clock.`
> 
> We need to be careful with 'activated before probing the PHY'. phylib
> itself will not activate the clock. You must be putting the IDs into
> the compatible string, so the correct driver is loaded, and its probe
> function is called. The probe itself enables the clock, so it is not
> before probe, but during probe.
> 
> I'm picky about this because we have issues with enumerating the MDIO
> bus to find PHYs. Some boards needs the PHY taking out of reset,
> regulators enabled, clocks enabled etc, before the PHY will respond on
> the bus. It is hard for the core to do this, before the probe. So we
> recommend putting IDs in the compatible, so the driver probe function
> to do any additional setup needed.

That makes sense, In my head, "probing" == calling phy_write/read() functions. 
But I get how this could be confused with the _probe() function. (And I just 
realised that there are typos)

What about "Ethernet PHYs can have an external clock that needs to be 
activated before communicating with the PHY" ?

> > Signed-off-by: Detlev Casanova <detlev.casanova@...labora.com>
> > ---
> > 
> >  Documentation/devicetree/bindings/net/ethernet-phy.yaml | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > b/Documentation/devicetree/bindings/net/ethernet-phy.yaml index
> > 4f574532ee13..c1241c8a3b77 100644
> > --- a/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > +++ b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > 
> > @@ -93,6 +93,12 @@ properties:
> >        the turn around line low at end of the control phase of the
> >        MDIO transaction.
> > 
> > +  clocks:
> > +    maxItems: 1
> > +    description:
> > +      External clock connected to the PHY. If not specified it is assumed
> > +      that the PHY uses a fixed crystal or an internal oscillator.
> 
> This text is good.

Detlev