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From:   Bartosz Golaszewski <brgl@bgdev.pl>
Date:   Tue, 8 Aug 2023 14:16:50 +0200
Message-ID: <CAMRc=MdLky5sUbdFGFc+as906kr-J_XDmKmYtBBCHvETvqtAQA@mail.gmail.com>
Subject: Re: [PATCH 5/9] arm64: dts: qcom: sa8775p-ride: move the reset-gpios
 property of the PHY
To:     Andrew Halaney <ahalaney@redhat.com>
Cc:     Andrew Lunn <andrew@lunn.ch>, Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Alex Elder <elder@linaro.org>,
        Srini Kandagatla <srinivas.kandagatla@linaro.org>,
        linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
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On Tue, Aug 8, 2023 at 12:27=E2=80=AFAM Andrew Halaney <ahalaney@redhat.com=
> wrote:
>
> On Mon, Aug 07, 2023 at 11:51:40PM +0200, Andrew Lunn wrote:
> > > > I have proposed a solution for this problem in 2020 but it never go=
t
> > > > upstream. Now we have a workaround in place which allows us to hard=
-code
> > > > the PHY id in the compatible property, thus skipping the ID scannin=
g).
> > >
> > > nitpicky, but I think that already existed at that time :D
> >
> > Yes, it has been there are long long time. It is however only in the
> > last 5 years of so has it been seen as a solution to the chicken egg
> > problem.
> >
> > > >           sgmii_phy: phy@8 {
> > > > +                 compatible =3D "ethernet-phy-id0141.0dd4";
> > > >                   reg =3D <0x8>;
> > > >                   device_type =3D "ethernet-phy";
> > > > +                 reset-gpios =3D <&pmm8654au_2_gpios 8 GPIO_ACTIVE=
_LOW>;
> > > > +                 reset-deassert-us =3D <70000>;
> > >
> > > Doesn't this need reset-assert-us?
> >
> > If i remember correctly, there is a default value if DT does not
> > provide one.
> >
>
> I've been trying to make sure I view devicetree properties as an OS
> agnostic ABI lately, with that in mind...
>
> The dt-binding says this for ethernet-phy:
>
>   reset-assert-us:
>     description:
>       Delay after the reset was asserted in microseconds. If this
>       property is missing the delay will be skipped.
>
> If the hardware needs a delay I think we should encode it based on that
> description, else we risk it starting to look like a unit impulse!
>

Please note that the mdio-level delay properties are not the same as
the ones on the PHY levels.

reset-delay-us - this is the delay BEFORE *DEASSERTING* the reset line
reset-post-delay-us - this is the delay AFTER *DEASSERTING* the reset line

On PHY level we have:

reset-assert-us - AFTER *ASSERTING*
reset-deassert-us - AFTER *DEASSERTING*

There never has been any reset-assert delay on that line before. It
doesn't look like we need a delay BEFORE deasserting the line, do we?

Bart