linux-kernel - Re: [PATCH v1] RFC: of: property: fix phy-hanlde issue

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Message-ID: <CAGETcx-qDPETtsSPKyW+6i=c=x2LG-tcJ+zCu40jCa9FwA-bEA@mail.gmail.com>
Date:   Mon, 13 Sep 2021 21:44:07 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>, kernel-team@...roid.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] RFC: of: property: fix phy-hanlde issue

On Mon, Sep 13, 2021 at 5:54 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> On Thu, Sep 9, 2021 at 1:03 AM Marek Szyprowski
> <m.szyprowski@...sung.com> wrote:
> >
> > Hi
> >
> > On 08.09.2021 23:58, Saravana Kannan wrote:
> > > This is a test patch. I'll split it up into multiple commits and clean
> > > it up once it's shown to help.
> > >
> > > Marek, can you please test this and let me know if it helps?
> > I've just checked and nope, it doesn't help for my case. Ethernet is
> > still not probed on Amlogic G12A/B SoC based boards. :(
>
> Hi Marek,
>
> Thanks for testing out the patch. Turns out the issue was a lot more
> complicated than I thought. Thanks to a bunch of debug logs that Rob
> provided off-list, I was able to root cause the actual issue.
>
> Looks like the problem is cyclic dependency between the mdio-multiplexer and the
> ethernet:
> ethmac -(phy-handle)-> external_phy -(parent) ->
> mdio-multiplexer -(mdio-bus-parent)-> mdio0 -(parent)-> ethmac
>
> Relevant parts of the DT combined from multiple files and trimmed and
> pasted below.
>
> If fw_devlink sees a cycle, it'll stop enforcing ordering between all
> the devices in the cycle since it can't figure out which one of the
> dependencies isn't real. So, the confusing part was that, when Andrew
> Lunn gave the patch for adding support for "mdio-bus-parent", that
> should have allowed fw_devlink to see the cycle and stop enforcing the
> dependencies. But that didn't happen because of a bug in fw_devlink
> cycle handling (it worked for most cases, but not for this specific
> ordering in DT). I'll send out a fix for that soon.

Here's the fix I promised:
https://lore.kernel.org/lkml/20210914043928.4066136-2-saravanak@google.com/

> That combined with
> Andrew's "mdio-bus-parent" patch should fix things for you.

Fairly certain the fix above and Andrew's patch should fix it for you
if you want to test it. Rob already verified a very similar patch for me.

-Saravana

> But I
> think I'll revert the phy-handle patch for other reasons (I'll explain
> that in the patch that reverts it).
>
>
> Thanks,
> Saravana
>
> ethmac: ethernet@...f0000 {
>     compatible = "amlogic,meson-g12a-dwmac"
>
>     phy-handle = <&external_phy>;
>     mdio0: mdio {
>         compatible = "snps,dwmac-mdio";
>     }
> };
>
> mdio-multiplexer {
>     mdio-bus-parent = <&mdio0>;
>
>     ext_mdio: mdio@0 {
>         /* no compatible prop */
>         external_phy: ethernet-phy@0 {
>             /* no compatible prop */
>         }
>     }
> }
>
> -Saravana