Date:   Thu, 24 Aug 2017 20:05:28 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     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 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?
-- 
Florian

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