linux-kernel - Re: [RESEND PATCH 2/2] soc: qcom: rpmhpd: Make power

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Date:   Fri, 13 Aug 2021 11:45:54 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH 2/2] soc: qcom: rpmhpd: Make power_on actually
 enable the domain

On Thu, 12 Aug 2021 at 15:21, Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
>
> On 03/07/2021 05:54, Bjorn Andersson wrote:
> > The general expectation is that powering on a power-domain should make
> > the power domain deliver some power, and if a specific performace state
> > is needed further requests has to be made.
> >
> > But in contrast with other power-domain implementations (e.g. rpmpd) the
> > RPMh does not have an interface to enable the power, so the driver has
> > to vote for a particular corner (performance level) in rpmh_power_on().
> >
> > But the corner is never initialized, so a typical request to simply
> > enable the power domain would not actually turn on the hardware. Further
> > more, when no more clients vote for a performance state (i.e. the
> > aggregated vote is 0) the power domain would be turn off.
> >
> > Fix both of these issues by always voting for a corner with non-zero
> > value, when the power domain is enabled.
> >
> > The tracking of the lowest non-zero corner is performed to handle the
> > corner case if there's ever a domain with a non-zero lowest corner, in
> > which case both rpmh_power_on() and rpmh_rpmhpd_set_performance_state()
> > would be allowed to use this lowest corner.
> >
> > Fixes: 279b7e8a62cc ("soc: qcom: rpmhpd: Add RPMh power domain driver")
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> >
> > Resending because the hunk in rpmhpd_update_level_mapping() was left in the
> > index.
>
> So, colleagues, what is the fate of this patch? Is it going to be
> applied? Or we agree that current approach (power_on +
> set_performance_state) is the expected behaviour? My patches on gdsc
> rework depend on this patch, but I can rework in them in favour of
> required-opp approach.

Today, genpd treats performance states and power on/off states as
orthogonal. You know this already, ofcourse.

Although, to clarify, this means that the genpd provider has to deal
with the scenario when its ->set_performance_state() callback may be
invoked, while the PM domain is turned off, for example. Similarly,
genpd may power on the PM domain by invoking the ->power_on()
callback, before the ->set_performance_state() has been invoked. And
finally, the power domain may be turned off even if there are some
active votes for a performance state.

So for now, the genpd provider needs to deal with these cases. Yes, we
have discussed changing the behaviour in genpd around this and I think
there have been some good reasons for it, but we are not there, at
least yet.

[...]

Kind regards
Uffe