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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Thu, 28 Oct 2021 12:35:11 +0200
Message-ID: <CAPDyKFoMpmkHgUbRN4pxgW2Gy=aZpS=eVwQrg0ydFbh9_GFG6Q@mail.gmail.com>
Subject: Re: [PATCH v2 1/3] dt-bindings: usb: qcom,dwc3: Add multi-pd bindings
 for dwc3 qcom
To:     Rajendra Nayak <rnayak@codeaurora.org>
Cc:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Sandeep Maheswaram <quic_c_sanm@quicinc.com>,
        Rob Herring <robh+dt@kernel.org>,
        Andy Gross <agross@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Felipe Balbi <balbi@kernel.org>,
        Doug Anderson <dianders@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        quic_pkondeti@quicinc.com, quic_ppratap@quicinc.com
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[...]

> >>> Got it. So in this case we could have the various display components
> >>> that are in the mdss gdsc domain set their frequency via OPP and then
> >>> have that translate to a level in CX or MMCX. How do we parent the power
> >>> domains outside of DT? I'm thinking that we'll need to do that if MMCX
> >>> is parented by CX or something like that and the drivers for those two
> >>> power domains are different. Is it basic string matching?
> >>
> >> In one way or another we need to invoke pm_genpd_add_subdomain() to link
> >> the two power-domains (actually genpds) together, like what was done in
> >> 3652265514f5 ("clk: qcom: gdsc: enable optional power domain support").
> >>
> >> In the case of MMCX and CX, my impression of the documentation is that
> >> they are independent - but if we need to express that CX is parent of
> >> MMCX, they are both provided by rpmhpd which already supports this by
> >> just specifying .parent on mmcx to point to cx.
> >
> > I was trying to follow the discussion, but it turned out to be a bit
> > complicated to catch up and answer all things. In any case, let me
> > just add a few overall comments, perhaps that can help to move things
> > forward.
> >
> > First, one domain can have two parent domains. Both from DT and from
> > genpd point of view, just to make this clear.
> >
> > Although, it certainly looks questionable to me, to hook up the USB
> > device to two separate power domains, one to control power and one to
> > control performance. Especially, if it's really the same piece of HW
> > that is managing both things.
> []..
> > Additionally, if it's correct to model
> > the USB GDSC power domain as a child to the CX power domain from HW
> > point of view, we should likely do that.
>
> I think this would still require a few things in genpd, since
> CX and USB GDSC are power domains from different providers.
> Perhaps a pm_genpd_add_subdomain_by_name()?
>

I think of_genpd_add_subdomain() should help to address this. No?

Kind regards
Uffe