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

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Message-ID: <CAMuHMdWWfaP8=H7H+UzrmOYpydi2mGLFGzuk9FQWJtEOug6u5g@mail.gmail.com>
Date:   Tue, 23 May 2017 11:36:47 +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 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?

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