linux-kernel - Re: [PATCH] OPP: Fix support for required OPPs for multiple PM domains

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Message-ID: <20240729060550.crgrmbnlv66645w2@vireshk-i7>
Date: Mon, 29 Jul 2024 11:35:50 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
	Stephen Boyd <sboyd@...nel.org>, Nikunj Kela <nkela@...cinc.com>,
	Prasad Sodagudi <psodagud@...cinc.com>, linux-pm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] OPP: Fix support for required OPPs for multiple PM
 domains

On 28-07-24, 22:05, Ulf Hansson wrote:
> > > > I think that design is rather correct, just like other frameworks. Just that we
> > > > need to do only set-level for genpds and nothing else. That will have exactly
> > > > the same behavior that you want.
> > >
> > > I don't quite understand what you are proposing. Do you want to add a
> > > separate path for opp-levels?
> >
> > Not separate paths, but ignore clk/regulator changes if the table belongs to a
> > genpd.
> >
> > > The problem with that would be that platforms (Tegra at least) are
> > > already using a combination of opp-level and clocks.
> >
> > If they are using both for a genpd's OPP table (and changes are made for both
> > opp-level and clock by the OPP core), then it should already be wrong, isn't it?
> 
> They are changing the clock through the device's OPP table and the
> level (performance-state) via genpd's table (using required OPPs).
> This works fine as of today.

There is a problem here I guess then. Lets say there are two devices A and B,
that depend on a genpd.

A requests required OPP 5 (level 5, clk 1.4 GHz), followed by 
B requests required OPP 3 (level 3, clk 1 GHz).

After this level will be configured to 5 and clk to 1 GHz I think.

> It's working today for *opp-level* only, because of the commit above.
> That's correct.

Good.

> My point is that calling dev_pm_opp_set_opp() recursively from
> _set_required_opps() doesn't make sense for the single PM domain case,
> as we can't assign a required-dev for it. This leads to an
> inconsistent behaviour when managing the required-OPPs.

We won't be calling that because of the above patch. In case of a single dev,
the required device isn't set and so we will never end up calling
dev_pm_opp_set_opp() for a single genpd case.

-- 
viresh