netdev - Re: [PATCH v6 05/21] net-next: stmmac: Add dwmac-sun8i

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Date:   Tue, 27 Jun 2017 16:11:21 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Corentin Labbe <clabbe.montjoie@...il.com>
Cc:     André Przywara <andre.przywara@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        alexandre.torgue@...com, devicetree <devicetree@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Icenowy Zheng <icenowy@...c.xyz>
Subject: Re: [PATCH v6 05/21] net-next: stmmac: Add dwmac-sun8i

On Tue, Jun 27, 2017 at 4:05 PM, Corentin Labbe
<clabbe.montjoie@...il.com> wrote:
> On Mon, Jun 26, 2017 at 01:18:23AM +0100, André Przywara wrote:
>> On 31/05/17 08:18, Corentin Labbe wrote:
>> > The dwmac-sun8i is a heavy hacked version of stmmac hardware by
>> > allwinner.
>> > In fact the only common part is the descriptor management and the first
>> > register function.
>>
>> Hi,
>>
>> I know I am a bit late with this, but while adapting the U-Boot driver
>> to the new binding I was wondering about the internal PHY detection:
>>
>>
>> So here you seem to deduce the usage of the internal PHY by the PHY
>> interface specified in the DT (MII = internal, RGMII = external).
>> I think I raised this question before, but isn't it perfectly legal for
>> a board to use MII with an external PHY even on those SoCs that feature
>> an internal PHY?
>> On the first glance that does not make too much sense, but apart from
>> not being the correct binding to describe all of the SoCs features I see
>> two scenarios:
>> 1) A board vendor might choose to not use the internal PHY because it
>> has bugs, lacks features (configurability) or has other issues. For
>> instance I have heard reports that the internal PHY makes the SoC go
>> rather hot, possibly limiting the CPU frequency. By using an external
>> MII PHY (which are still cheaper than RGMII PHYs) this can be avoided.
>> 2) A PHY does not necessarily need to be directly connected to
>> magnetics. Indeed quite some boards use (RG)MII to connect to a switch
>> IC or some other network circuitry, for instance fibre connectors.
>>
>> So I was wondering if we would need an explicit:
>>       allwinner,use-internal-phy;
>> boolean DT property to signal the usage of the internal PHY?
>> Alternatively we could go with the negative version:
>>       allwinner,disable-internal-phy;
>>
>> Or what about introducing a new "allwinner,internal-mii-phy" compatible
>> string for the *PHY* node and use that?
>>
>> I just want to avoid that we introduce a binding that causes us
>> headaches later. I think we can still fix this with a followup patch
>> before the driver and its binding hit a release kernel.
>>
>> Cheers,
>> Andre.
>>
>
> I just see some patch, where "phy-mode = internal" is valid.
> I will try to find a way to use it

Can you provide a link?

I'm not a fan of using phy-mode for this. There's no guarantee what
mode the internal PHY uses. That's what phy-mode is for.

In any case, we should fix this before 4.13 is released.

ChenYu