linux-kernel - Re: [PATCH v2 1/3] dt-bindings: usb: qcom,dwc3: Add multi-pd bindings for dwc3 qcom

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Date:   Mon, 25 Oct 2021 13:17:00 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Sandeep Maheswaram <quic_c_sanm@...cinc.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Andy Gross <agross@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_pkondeti@...cinc.com, quic_ppratap@...cinc.com,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v2 1/3] dt-bindings: usb: qcom,dwc3: Add multi-pd bindings
 for dwc3 qcom

Quoting Bjorn Andersson (2021-10-25 12:10:35)
> On Mon 25 Oct 02:07 PDT 2021, Sandeep Maheswaram wrote:
>
> > Add multi pd bindings to set performance state for cx domain
> > to maintain minimum corner voltage for USB clocks.
> >
> > Signed-off-by: Sandeep Maheswaram <quic_c_sanm@...cinc.com>
> > ---
> > v2:
> > Make cx domain mandatory.
> >
> >  Documentation/devicetree/bindings/usb/qcom,dwc3.yaml | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml b/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml
> > index 2bdaba0..fd595a8 100644
> > --- a/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml
> > +++ b/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml
> > @@ -42,7 +42,13 @@ properties:
> >
> >    power-domains:
> >      description: specifies a phandle to PM domain provider node
> > -    maxItems: 1
> > +    minItems: 2
> > +    items:
> > +      - description: cx power domain
> > +      - description: USB gdsc power domain
> > +
> > +  required-opps:
> > +    description: specifies the performance state to power domain
>
> I'm still worried about the fact that we can't just rely on the USB GDSC
> being a subdomin of CX in order to just "turn on" CX.
>
> Afaict accepting this path forward means that for any device that sits
> in a GDSC power domain we will have to replicate this series for the
> related driver.
>

I suspect the problem is that it's not just "turn on" but wanting to
turn it on and then set the performance state to some value based on the
clk frequency. Maybe the simplest version of that could be supported
somehow by having dev_pm_opp_set_rate() figure out that the 'level'
applies to the parent power domain instead of the child one? Or we may
need to make another part of the OPP binding to indicate the
relationship between the power domain and the OPP and the parent of the
power domain.