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Date: Mon, 5 Feb 2024 14:08:30 +0530
From: Viresh Kumar <viresh.kumar@linaro.org>
To: Rob Herring <robh@kernel.org>
Cc: Saravana Kannan <saravanak@google.com>, David Dai <davidai@google.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Quentin Perret <qperret@google.com>,
	Masami Hiramatsu <mhiramat@google.com>,
	Will Deacon <will@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Marc Zyngier <maz@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Pavan Kondeti <quic_pkondeti@quicinc.com>,
	Gupta Pankaj <pankaj.gupta@amd.com>, Mel Gorman <mgorman@suse.de>,
	kernel-team@android.com, linux-pm@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 1/2] dt-bindings: cpufreq: add virtual cpufreq device
Message-ID: <20240205083830.4werub5e76kudjq4@vireshk-i7>
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 <20240131170608.GA1441369-robh@kernel.org>
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On 02-02-24, 09:53, Rob Herring wrote:
> On Wed, Jan 31, 2024 at 10:23:03AM -0800, Saravana Kannan wrote:
> > We also need the OPP tables to indicate which CPUs are part of the
> > same cluster, etc. Don't want to invent a new "protocol" and just use
> > existing DT bindings.
> 
> Topology binding is for that.

This one, right ?

Documentation/devicetree/bindings/dvfs/performance-domain.yaml

> You need per CPU Fmax, sure. But all the frequencies? I don't follow why 
> you don't just have a max available capacity and then request the 
> desired capacity. Then the host maps that to an underlying OPP. Why have 
> an intermediate set of fake frequencies?

+1

> As these are normalized, I guess you are normalizing for capacity as 
> well? Or you are using "capacity-dmips-mhz"? 
> 
> I'm also lost how this would work when you migrate and the underlying 
> CPU changes. The DT is fixed.
> 
> > > Also, we have "opp-level" for opaque values that aren't Hz.
> > 
> > Still want to keep it Hz to be compatible with arch_freq_scale and
> > when virtualized CPU perf counters are available.

These are all specific to a driver only, that can be handled easily I guess. I
don't see a value to using Hz for this to be honest.

-- 
viresh