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

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Message-ID: <20231106070830.7sd3ux3nvywpb54z@vireshk-i7>
Date:   Mon, 6 Nov 2023 12:38:30 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Stephan Gerhold <stephan@...hold.net>,
        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 03-11-23, 12:58, Ulf Hansson wrote:
> Are you saying that the OPP library should be capable of managing the
> parent-clock-rates too, when there is a new rate being requested for a
> clock that belongs to an OPP? To me, that sounds like replicating
> framework specific knowledge into the OPP library, no? Why do we want
> this?

I am surely not touching clocks or any other framework :)

> Unless I totally misunderstood your suggestion, I think it would be
> better if the OPP library remained simple and didn't run recursive
> calls, but instead relied on each framework to manage the aggregation
> and propagation to parents.

I see your point and agree with it.

Here is the problem and I am not very sure what's the way forward for this then:

- Devices can have other devices (like caches) or genpds mentioned via
  required-opps.

- Same is true for genpds, they can also have required-opps, which may or may not
  be other genpds.

- When OPP core is asked to set a device's OPP, it isn't only about performance
  level, but clk, level, regulator, bw, etc. And so a full call to
  dev_pm_opp_set_opp() is required.

- The OPP core is going to run the helper recursively only for required-opps and
  hence it won't affect clock or regulators.

- But it currently affects genpds as they are mentioned in required-opps.

- Skipping the recursive call to a parent genpd will require a special hack,
  maybe we should add it, I am just discussing it if we should or if there is
  another way around this.

-- 
viresh