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

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Date:   Thu, 24 Aug 2017 21:44:41 +0200
From:   Corentin Labbe <clabbe.montjoie@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        maxime.ripard@...e-electrons.com, andrew@...n.ch, wens@...e.org
Cc:     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 Thu, Aug 24, 2017 at 10:21:24AM +0200, Corentin Labbe wrote:
> On Wed, Aug 23, 2017 at 09:31:53AM -0700, Florian Fainelli wrote:
> > 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?
> 
> No, I tested and for example with sun8i-h3-orangepi-plus.dts, the external PHY (ethernet-phy@1) is still merged.
> So that adding a 'status = "disabled"' does not bring anything.
> 
> > 
> > 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
> 
> For me, if we want to represent the reality, we need two MDIO:
> - since two PHY at the same address could co-exists
> - since they are isolated so not on the same MDIO bus
> 
> > - 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
> 
> My patch for stmmac is really small, only the name of my variable ("need_mdio_mux_ids")
> have to be changed to something like "register_parent_mdio"
> 
> 
> So I agree with Maxime, we need to avoid merging PHY nodes, and we can avoid it only by having two separate MDIO nodes.
> Furthermore, with only one MDIO, we will face with lots of small patch for adding phy-is-integrated, with two we do not need to change any board DT, all is simply clean.
> Really having two MDIO seems cleaner.
> 

Hello

I have speaked with Neil Amstrong, and he said that they get the same problem on amlogic.
They use a mdio-mux-mmioreg, (see eth-phy-mux in arch/arm64/boot/dts/amlogic/meson-gxl.dtsi)
So tomorow, i will send a patch series which do the same with the exception that we need a mdio-mux-syscon (which is easy/simple to do).
Since their setup use stmmac, it means that we will need 0 changes on stmmac.

Regards