netdev - Re: [PATCH 2/4] Revert "arm64: dts: renesas: Add compatible properties to AR8031 Ethernet PHYs"

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Date:   Fri, 6 Jan 2023 15:45:05 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Adam Ford <aford173@...il.com>
Cc:     linux-renesas-soc@...r.kernel.org, aford@...conembedded.com,
        Magnus Damm <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/4] Revert "arm64: dts: renesas: Add compatible
 properties to AR8031 Ethernet PHYs"

Hi Adam,

On Fri, Jan 6, 2023 at 3:35 PM Adam Ford <aford173@...il.com> wrote:
> On Fri, Jan 6, 2023 at 8:28 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Wed, Jan 4, 2023 at 3:12 PM Adam Ford <aford173@...il.com> wrote:
> > > This reverts commit 18a2427146bf8a3da8fc7825051d6aadb9c2d8fb.
> > >
> > > Due to the part shortage, the AR8031 PHY was replaced with a
> > > Micrel KSZ9131.  Hard-coding the ID of the PHY makes this new
> > > PHY non-operational.  Since previous hardware had shipped,
> > > it's not as simple as just replacing the ID number as it would
> > > break the older hardware.  Since the generic mode can correctly
> > > identify both versions of hardware, it seems safer to revert
> > > this patch.
> > >
> > > Signed-off-by: Adam Ford <aford173@...il.com>
> >
> > Thanks for your patch!
> >
> > > --- a/arch/arm64/boot/dts/renesas/beacon-renesom-som.dtsi
> > > +++ b/arch/arm64/boot/dts/renesas/beacon-renesom-som.dtsi
> > > @@ -59,8 +59,6 @@ &avb {
> > >         status = "okay";
> > >
> > >         phy0: ethernet-phy@0 {
> > > -               compatible = "ethernet-phy-id004d.d074",
> > > -                            "ethernet-phy-ieee802.3-c22";
> > >                 reg = <0>;
> > >                 interrupt-parent = <&gpio2>;
> > >                 interrupts = <11 IRQ_TYPE_LEVEL_LOW>;
> >
> > The next line:
> >
> >                 reset-gpios = <&gpio2 10 GPIO_ACTIVE_LOW>;
> >
> > Unfortunately, removing the compatible value will cause regressions
> > for kexec/kdump and for Ethernet driver unbind, as the PHY reset will
> > be asserted before starting the new kernel, or on driver unbind.
> > Due to a deficiency in the Ethernet PHY subsystem, the PHY will be
> > probed while the reset is still asserted, and thus fail probing[1].
>
> FWIW, the bootloader brings the device out of reset.  Would it be

The bootloader is not involved when using kexec/kdump, or when
unbinding the Ethernet driver.

> sufficient to keep  "ethernet-phy-ieee802.3-c22" and drop the
> hard-coded ID?

I am afraid not, as that still requires actual probing to determine
the PHY ID.

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