Re: [PATCH 1/2] OPP: Use _set_opp_level() for single genpd case

From: Viresh Kumar <viresh.kumar@linaro.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Stephan Gerhold <stephan@gerhold.net>,
	Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-pm@vger.kernel.org,
	Vincent Guittot <vincent.guittot@linaro.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Stephan Gerhold <stephan.gerhold@kernkonzept.com>,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] OPP: Use _set_opp_level() for single genpd case
Date: Mon, 6 Nov 2023 12:38:30 +0530	[thread overview]
Message-ID: <20231106070830.7sd3ux3nvywpb54z@vireshk-i7> (raw)
In-Reply-To: <CAPDyKFrn97POKuNc3cMM9TOaw-f-ufLwYtUY8_L2w8+hzECWOA@mail.gmail.com>

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