linux-kernel - Re: [PATCH v4 2/2] arm64: dts: sc7180: Add required-opps for i2c

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Date:   Fri, 16 Jul 2021 15:52:12 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Rajendra Nayak <rnayak@...eaurora.org>, ulf.hansson@...aro.org,
        viresh.kumar@...aro.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, rojay@...eaurora.org,
        stephan@...hold.net
Subject: Re: [PATCH v4 2/2] arm64: dts: sc7180: Add required-opps for i2c

On Fri 16 Jul 15:21 CDT 2021, Stephen Boyd wrote:

> Quoting Bjorn Andersson (2021-07-16 13:18:56)
> > On Fri 16 Jul 05:00 CDT 2021, Rajendra Nayak wrote:
> >
> > > qup-i2c devices on sc7180 are clocked with a fixed clock (19.2 MHz)
> > > Though qup-i2c does not support DVFS, it still needs to vote for a
> > > performance state on 'CX' to satisfy the 19.2 Mhz clock frequency
> > > requirement.
> > >
> >
> > Sounds good, but...
> >
> > > Use 'required-opps' to pass this information from
> > > device tree, and also add the power-domains property to specify
> > > the CX power-domain.
> > >
> >
> > ..is the required-opps really needed with my rpmhpd patch in place?
> >
> 
> Yes? Because rpmhpd_opp_low_svs is not the lowest performance state for
> CX.

On e.g. sm8250 the first available non-zero corner presented in cmd-db
is low_svs.

And if this (which?) clock requires a higher corner than the lowest
possible in order to tick at this "lowest" frequency, I'm certainly
interested in some more details.

Regards,
Bjorn