linux-kernel - Re: [PATCH 1/2] OPP: Use _set_opp

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Date:   Fri, 20 Oct 2023 13:09:13 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Stephan Gerhold <stephan.gerhold@...nkonzept.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] OPP: Use _set_opp_level() for single genpd case

On Fri, 20 Oct 2023 at 12:57, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 20-10-23, 12:02, Ulf Hansson wrote:
> > For the single PM domain case, consumer drivers are often not able to
> > use dev_pm_opp_set_config(). That's because the PM domain has already
> > been attached from some of the generic buses, through
> > dev_pm_domain_attach().
> >
> > In this case, as dev_pm_opp_set_config() ends up trying to attach
> > again, via dev_pm_domain_attach_by_name() it would receive
> > "ERR_PTR(-EEXIST)".
> >
> > Or maybe I didn't quite understand your point?
>
> So the thing is that I _really_ want to call dev_pm_opp_set_opp() for
> each OPP we want to configure, primary or required. For example, the
> required OPP may want to do more than just performance state and we
> aren't touching them right now.

I understand - and it makes perfect sense to me too!

>
> Now, in order to call dev_pm_opp_set_opp() for any device, we need a
> device pointer and an OPP table associated with it.
>
> I can take care of it for the multi genpd case as there are extra
> device structures (which we get from dev_pm_domain_attach_by_name()),
> but there is no clean way out for single PM domain devices, unless
> they also call dev_pm_opp_set_config() to get a virtual structure.
>
> This is why I had to get this hackish code in place to make it work
> with the recursive calls to dev_pm_opp_set_opp(), where I could just
> reuse the opp-level thing for the primary device.
>
> How do you suggest we take care of this now ?

Honestly, I don't know yet. But I am certainly willing to help. Allow
me to have a closer look and see if I can propose a way forward.

Kind regards
Uffe