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

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Date:   Mon, 13 Sep 2021 17:54:39 -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 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. That combined with
Andrew's "mdio-bus-parent" patch should fix things for you. 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