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

From: Florian Fainelli
Date: Sun Jul 09 2017 - 12:49:54 EST

On 07/02/2017 01:37 PM, Geert Uytterhoeven wrote:
> On Tue, Jun 6, 2017 at 11:43 AM, Geert Uytterhoeven
> <geert@xxxxxxxxxxxxxx> wrote:
>> On Tue, May 23, 2017 at 11:36 AM, Geert Uytterhoeven
>> <geert@xxxxxxxxxxxxxx> wrote:
>>> On Fri, May 19, 2017 at 12:21 AM, Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
>>>> On 05/18/2017 01:36 PM, Geert Uytterhoeven wrote:
>>>>> On Thu, May 18, 2017 at 9:34 PM, Andrew Lunn <andrew@xxxxxxx> 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
> 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?