netdev - Re: [PATCH v3 3/4] net: stmmac: register parent MDIO node for sun8i-h3-emac

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Date:   Wed, 23 Aug 2017 09:31:53 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     Corentin Labbe <clabbe.montjoie@...il.com>,
        Chen-Yu Tsai <wens@...e.org>, Andrew Lunn <andrew@...n.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] net: stmmac: register parent MDIO node for
 sun8i-h3-emac

On 08/23/2017 12:49 AM, Maxime Ripard wrote:
> Hi Florian,
> 
> On Tue, Aug 22, 2017 at 11:35:01AM -0700, Florian Fainelli wrote:
>>>>> So I think what you are saying is either impossible or engineering-wise
>>>>> a very stupid design, like using an external MAC with a discrete PHY
>>>>> connected to the internal MAC's MDIO bus, while using the internal MAC
>>>>> with the internal PHY.
>>>>>
>>>>> Now can we please decide on something? We're a week and a half from
>>>>> the 4.13 release. If mdio-mux is wrong, then we could have two mdio
>>>>> nodes (internal-mdio & external-mdio).
>>>>
>>>> I really don't see a need for a mdio-mux in the first place, just have
>>>> one MDIO controller (current state) sub-node which describes the
>>>> built-in STMMAC MDIO controller and declare the internal PHY as a child
>>>> node (along with 'phy-is-integrated'). If a different configuration is
>>>> used, then just put the external PHY as a child node there.
>>>>
>>>> If fixed-link is required, the mdio node becomes unused anyway.
>>>>
>>>> Works for everyone?
>>>
>>> If we put an external PHY with reg=1 as a child of internal MDIO,
>>> il will be merged with internal PHY node and get
>>> phy-is-integrated.
>>
>> Then have the .dtsi file contain just the mdio node, but no internal or
>> external PHY and push all the internal and external PHY node definition
>> (in its entirety) to the per-board DTS file, does not that work?
> 
> If possible, I'd really like to have the internal PHY in the
> DTSI. It's always there in hardware anyway, and duplicating the PHY,
> with its clock, reset line, and whatever info we might need in the
> future in each and every board DTS that uses it will be very error
> prone and we will have the usual bunch of issues that come up with
> duplication.

OK, then what if you put the internal PHY in the DTSI, mark it with a
status = "disabled" property, and have the per-board DTS put a status =
"okay" property along with a "phy-is-integrated" boolean property? Would
that work?

What I really don't think is necessary is:

- duplicating the "mdio" controller node for external vs. internal PHY,
because this is not accurate, there is just one MDIO controller, but
there may be different kinds of MDIO/PHY devices attached

- having the STMMAC driver MDIO probing code having to deal with a
"mdio" sub-node or an "internal-mdio" sub-node because this is confusing
and requiring more driver-level changes that are error prone

Thanks
-- 
Florian