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 17:31:59 +0100
From: Jérémie Dautheribes
 <jeremie.dautheribes@...tlin.com>
To: Andrew Lunn <andrew@...n.ch>
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.

Ok noted, thanks for your feedback! I will send a v2 containing a 
simplified description + implement your suggested changes on patch 2.

Jérémie