netdev - Re: [PATCH] of_mdio: Fix broken PHY IRQ in case of probe deferral

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Date:   Tue, 6 Jun 2017 11:43:22 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of_mdio: Fix broken PHY IRQ in case of probe deferral

Hi Florian,

On Tue, May 23, 2017 at 11:36 AM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> On Fri, May 19, 2017 at 12:21 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
>> On 05/18/2017 01:36 PM, Geert Uytterhoeven wrote:
>>> On Thu, May 18, 2017 at 9:34 PM, Andrew Lunn <andrew@...n.ch> wrote:
>>>>>> This most certainly works fine in the simple case where you have one PHY
>>>>>> hanging off the MDIO bus, now what happens if you have several?
>>>>>>
>>>>>> Presumably, the first PHY that returns EPROBE_DEFER will make the entire
>>>>>> bus registration return EPROB_DEFER as well, and so on, and so forth,
>>>>>> but I am not sure if we will be properly unwinding the successful
>>>>>> registration of PHYs that either don't have an interrupt, or did not
>>>>>> return EPROBE_DEFER.
>>>>>>
>>>>>> It should be possible to mimic this behavior by using the fixed PHY, and
>>>>>> possibly the dsa_loop.c driver which would create 4 ports, expecting 4
>>>>>> fixed PHYs to be present.
>>>>>
>>>>> mdiobus_unregister(), called from of_mdiobus_register() on failure,
>>>>> should do the unwinding, right?
>>>>>
>>>>> And when the driver is reprobed, all PHYs are reprobed, until they all
>>>>> succeed.
>>>>
>>>> That is the theory. I looked at that while reviewing the patch. But
>>>> this has probably not been tested in anger. It would be good to test
>>>> this properly, with not just the first PHY returning -EPROBE_DEFER, to
>>>> really test the unwind.
>>>
>>> Unfortunately I don't have a board with multiple PHYs, so I cannot test
>>> that case.
>
> I tried adding a few dummy PHYs in DT, but that didn't work.
>
> So how can we proceed?
>
> I think the only way my patch can cause issues is because some systems
> may rely on EPROBE_DEFER errors being ignored.
>
>>> Does unbinding/rebinding a network driver with multiple PHYs currently
>>> work? Or module unload/reload?
>>
>> Usually there is a strict 1:1 mapping between a network device (not
>> driver) and a PHY device, switch drivers however, would have multiple
>> PHYs (one per port, aka net_deice).
>>
>> NB: binding and unbinding of PHYs is pretty broken at the moment though,
>> because there is a complete disconnect between what the Ethernet MAC
>> expects, and the state in which the PHY is. I had some patches to fix
>> that, but this turned out to be playing whack-a-mole which I typically
>> suck at.
>
> I didn't mean unbinding the PHY, but the network device.
> Don't you have the same issue with the state of PHYs as left by the bootloader?

Anyone who can test the behavior on an Ethernet device with multiple PHYs,
e.g. by faking an -EPROBE_DEFER somewhere in the middle?

I'd like to get this issue fixed in v4.13, to avoid a regression when migrating
several systems to a new and better clock driver in v4.14, which will trigger
EPROBE_DEFER.

Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds