linux-kernel - Re: [PATCH v2] of: property: fw_devlink: Add support for "phy-handle" property

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Message-ID: <CAGETcx_eUE1gLAaqXdLjCb2XxttH20066kXs969khnrEZQ71mA@mail.gmail.com>
Date:   Mon, 23 Aug 2021 11:13:08 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>, netdev@...r.kernel.org,
        kernel-team@...roid.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH v2] of: property: fw_devlink: Add support for "phy-handle" property

On Mon, Aug 23, 2021 at 6:16 AM Andrew Lunn <andrew@...n.ch> wrote:
>
> On Mon, Aug 23, 2021 at 02:08:48PM +0200, Marek Szyprowski wrote:
> > Hi,
> >
> > On 18.08.2021 04:17, Saravana Kannan wrote:
> > > Allows tracking dependencies between Ethernet PHYs and their consumers.
> > >
> > > Cc: Andrew Lunn <andrew@...n.ch>
> > > Cc: netdev@...r.kernel.org
> > > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> >
> > This patch landed recently in linux-next as commit cf4b94c8530d ("of:
> > property: fw_devlink: Add support for "phy-handle" property"). It breaks
> > ethernet operation on my Amlogic-based ARM64 boards: Odroid C4
> > (arm64/boot/dts/amlogic/meson-sm1-odroid-c4.dts) and N2
> > (meson-g12b-odroid-n2.dts) as well as Khadas VIM3/VIM3l
> > (meson-g12b-a311d-khadas-vim3.dts and meson-sm1-khadas-vim3l.dts).
> >
> > In case of OdroidC4 I see the following entries in the
> > /sys/kernel/debug/devices_deferred:
> >
> > ff64c000.mdio-multiplexer
> > ff3f0000.ethernet
> >
> > Let me know if there is anything I can check to help debugging this issue.
>
> Hi Marek
>
> Please try this. Completetly untested, not even compile teseted:
>
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 0c0dc2e369c0..7c4e257c0a81 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1292,6 +1292,7 @@ DEFINE_SIMPLE_PROP(resets, "resets", "#reset-cells")
>  DEFINE_SIMPLE_PROP(leds, "leds", NULL)
>  DEFINE_SIMPLE_PROP(backlight, "backlight", NULL)
>  DEFINE_SIMPLE_PROP(phy_handle, "phy-handle", NULL)
> +DEFINE_SIMPLE_PROP(mdio_parent_bus, "mdio-parent-bus", NULL);
>  DEFINE_SUFFIX_PROP(regulators, "-supply", NULL)
>  DEFINE_SUFFIX_PROP(gpio, "-gpio", "#gpio-cells")
>
> @@ -1381,6 +1382,7 @@ static const struct supplier_bindings of_supplier_bindings[] = {
>         { .parse_prop = parse_leds, },
>         { .parse_prop = parse_backlight, },
>         { .parse_prop = parse_phy_handle, },
> +       { .parse_prop = parse_mdio_parent_bus, },
>         { .parse_prop = parse_gpio_compat, },
>         { .parse_prop = parse_interrupts, },
>         { .parse_prop = parse_regulators, },

Looking at the code, I'm fairly certain that the device that
corresponds to a DT node pointed to by mdio-parent-bus will be a "bus"
device that's registered with the mdio_bus_class.

If my understanding is right, then Nak for this patch. It'll break a
lot of probes.

TL;DR is that stateful/managed device links don't make sense for
devices that are never probed/bound to a driver. I plan to improve
device links to try and accommodate these cases nicely, but that's in
my TO DO list. Until that's completed, this patch will break stuff.

-Saravana