linux-kernel - Re: [PATCH v3 1/3] dt-bindings: phy: qcom,qmp: Add PCIe qcom,refclk-always-on property

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Date:   Thu, 7 Dec 2023 14:05:12 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Krishna Chaitanya Chundru <quic_krichai@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_vbadigan@...cinc.com, quic_ramkri@...cinc.com,
        quic_nitegupt@...cinc.com, quic_skananth@...cinc.com,
        quic_vpernami@...cinc.com, quic_parass@...cinc.com
Subject: Re: [PATCH v3 1/3] dt-bindings: phy: qcom,qmp: Add PCIe
 qcom,refclk-always-on property

On Thu, Dec 07, 2023 at 03:42:52PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Dec 07, 2023 at 10:51:09AM +0100, Johan Hovold wrote:
> > On Wed, Dec 06, 2023 at 06:40:09PM +0530, Manivannan Sadhasivam wrote:
> > 
> > > OK. How about, "qcom,broken-refclk"? This reflects the fact that the default
> > > refclk operation is broken on this platform, so the OS should be prepared for
> > > it (by keeping it always on).
> > 
> > Shouldn't that be
> > 
> > 	qcom,broken-clkreq
> > 
> > since its the CLKREQ# signal used to request REFCLK that is broken, not
> > the REFCLK itself?
> > 
> 
> Darn... You are right. I got carried away by the initial property name. Thanks
> for spotting!

Thinking some more on this after hitting send: It may still be wrong
with a 'broken-clkreq' property in the PHY instead of in the controller
(or endpoint).

Could there not be other ways to handle a broken clkreq signal so that
this really should be a decision made by the OS, for example, to disable
L1 substates and clock PM?

Simply leaving the refclk always on in the PHY seems like a bit of a
hack and I'm not even sure that can be considered correct.

Having a property that maps directly to that behaviour has rightly been
rejected, but it seems that simply renaming the flag but keeping it in
the PHY may still not be the right thing to do here.

Johan