Date:   Fri, 25 Aug 2017 11:41:39 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        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 Fri, Aug 25, 2017 at 11:05 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
>
>
> On 08/24/2017 07:54 PM, Chen-Yu Tsai wrote:
>> On Fri, Aug 25, 2017 at 3:59 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
>>> On 08/24/2017 01:21 AM, 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.
>>>
>>> Is not there is a mistake in the unit address not matching the "reg"
>>> property, or am I not looking at the right tree?
>>>
>>> &mdio {
>>>         ext_rgmii_phy: ethernet-phy@1 {
>>>                 compatible = "ethernet-phy-ieee802.3-c22";
>>>                 reg = <0>;
>>>         };
>>> };
>>>
>>> If the PHY is really at MDIO address 0, then it should be
>>> ethernet-phy@0, and not ethernet-phy@1, and then no problem with the
>>> merging?
>>
>> That is wrong. The board described in the example likely has a Realtek
>> RTL8211E @ address 0x1. Address 0 for this PHY is a broadcast address,
>> so it still works, but is the wrong representation.
>>
>>>
>>>
>>>> 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
>>>
>>> Is that really true? It might be, but from experience with e.g:
>>> bcmgenet, the integrated PHY and the external PHYs are on the same MDIO
>>> bus, which is convenient, except when you have an address conflict.
>>
>> There's a mux in the hardware: either the internal MDIO+MII lines
>> from the internal PHY are connected to the MAC, or the external
>> MDIO+MII lines from the pin controller are connected. I believe
>> this was already mentioned?
>
> There is obviously a mux for the data lines and clock to switch between
> internal PHY and external PHYs, that does not mean there is one for MDIO
> and MDC lines, which is what is being suggested to be used here, does
> the mux also takes care of these lines?
>
>>
>>>
>>>>
>>>>> - 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.
>>>
>>> The only valid thing that you have provided so far is this merging
>>> problem. Anything else ranging from "we will face with lots of small
>>> patch for adding phy-is-integrated" to "Really having two MDIO seems
>>> cleaner." are hard to receive as technical arguments for correctness.
>>>
>>> What happens if someone connects an external PHY at the same MDIO
>>> address than the internal PHY, which one do you get responses from? If
>>> you shutdown the internal PHY and it stops responding, then this
>>> probably becomes deterministic, but it still supports the fact there is
>>> just one MDIO bus controller per MAC.
>>
>> Depends on whichever set of pins/lines are selected. But yeah, there's
>> only one MDIO bus controller in the MAC.
>
> OK, so one MDIO controller, but what about the MDIO/MDC lines then, are
> they also muxed, like the data/clock lines or not?

Just tested. Yes the MDIO/MDC lines are also muxed and controlled through
the same mux bit.

ChenYu

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