linux-kernel - Re: [PATCH 5/9] arm64: dts: qcom: sa8775p-ride: move the reset-gpios property of the PHY

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Date:   Mon, 7 Aug 2023 17:27:44 -0500
From:   Andrew Halaney <ahalaney@...hat.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Alex Elder <elder@...aro.org>,
        Srini Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 5/9] arm64: dts: qcom: sa8775p-ride: move the reset-gpios
 property of the PHY

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 got
> > > 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 scanning).
> > 
> > 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 = "ethernet-phy-id0141.0dd4";
> > >  			reg = <0x8>;
> > >  			device_type = "ethernet-phy";
> > > +			reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
> > > +			reset-deassert-us = <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!