linux-kernel - Re: [PATCH net-next 1/3] dt-bindings: net: dp83822: support configuring RMII master/slave mode

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Date: Mon, 4 Mar 2024 17:06:36 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Jérémie Dautheribes <jeremie.dautheribes@...tlin.com>
Cc: "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>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>, Andrew Davis <afd@...com>,
	netdev@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Miquèl Raynal <miquel.raynal@...tlin.com>,
	Yen-Mei Goh <yen-mei.goh@...sight.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH net-next 1/3] dt-bindings: net: dp83822: support
 configuring RMII master/slave mode

> > We are normally interested in this 50Mhz reference clock. So i would
> > drop all references to 25Mhz. It is not relevant to the binding, since
> > it is nothing to do with connecting the PHY to the MAC, and it has a
> > fixed value.
> > 
> > So you can simplify this down to:
> > 
> > RMII Master: Outputs a 50Mhz Reference clock which can be connected to the MAC.
> > 
> > RMII Slave: Expects a 50MHz Reference clock input, shared with the
> > MAC.
> > 
> > > That said, would you like me to include this description (or some parts) in
> > > the binding in addition to what I've already written? Or would you prefer me
> > > to use a more meaningful property name?
> > 
> > We don't really have any vendor agnostic consistent naming. dp83867
> > and dp83869 seems to call this ti,clk-output-sel. Since this is
> > another dp83xxx device, it would be nice if there was consistency
> > between all these TI devices. So could you check if the concept is the
> > same, and if so, change dp83826 to follow what other TI devices do.
> 
> 
> So I had a look at this ti,clk-output-sel property on the TI DP8386x
> bindings, but unfortunately it does not correspond to our use case. In their
> case, it is used to select one of the various internal clocks to output on
> the CLK_OUT pin.
> In our case, we would prefer to describe the direction of the clock (OUT in
> master mode, IN in slave mode).

I would suggest we keep with the current property name, but simplify
the description. Focus on the reference clock, and ignore the crystal.

    Andrew