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

From: Geert Uytterhoeven
Date: Sun Jul 02 2017 - 16:38:56 EST

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


This patch fixes a real issue.




Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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