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

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Message-ID: <38cc7c65-e4ca-cb8a-f43b-ca53e87724cf@gmail.com>
Date:   Sun, 9 Jul 2017 09:49:35 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andrew Lunn <andrew@...n.ch>
Cc:     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



On 07/02/2017 01:37 PM, Geert Uytterhoeven wrote:
> On Tue, Jun 6, 2017 at 11:43 AM, Geert Uytterhoeven
> <geert@...ux-m68k.org> wrote:
>> 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.
> 
> Ping?
> 
> This patch fixes a real issue.

It sure does fix a real issue, but I am really concerned about the
inability to test this patch in a configuration where we have multiple
PHY(s) or MDIO device(s) hanging off the same MDIO bus and one of those
requesting an EPROBE_DEFER.

I currently don't have a setup where I could exercise this, Andrew, do you?
-- 
Florian