Re: [RFC] cpufreq: Add bindings for CPU clock sharing topology

From: Mike Turquette <mike.turquette@linaro.org>
To: Viresh Kumar <viresh.kumar@linaro.org>,
	Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Olof Johansson <olof@lixom.net>,
	Rob Herring <rob.herring@linaro.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Grant Likely <grant.likely@linaro.org>,
	"linaro-kernel@lists.linaro.org" <linaro-kernel@lists.linaro.org>,
	Nishanth Menon <nm@ti.com>, Sudeep Holla <Sudeep.Holla@arm.com>,
	Stephen Boyd <sboyd@codeaurora.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
	Arvind Chauhan <arvind.chauhan@arm.com>,
	Arnd Bergmann <arnd.bergmann@linaro.org>
Subject: Re: [RFC] cpufreq: Add bindings for CPU clock sharing topology
Date: Wed, 23 Jul 2014 17:33:14 -0700	[thread overview]
Message-ID: <20140724003314.6419.51564@quantum> (raw)
In-Reply-To: <CAKohpok-C+JCebjJkZExx6EjBctoyJF7fV71Vjj7bi1TAdXrFQ@mail.gmail.com>

Quoting Viresh Kumar (2014-07-20 05:07:32)
> On 19 July 2014 20:54, Santosh Shilimkar <santosh.shilimkar@ti.com> wrote:
> > Sorry for jumping late
> 
> No, you aren't late. Its just 2 days old thread :)
> 
> > but one of the point I was raising as part of your
> > other series was to extend the CPU topology bindings to cover the voltage
> > domain information which is probably what is really needed to let the
> > CPUfreq extract the information. Not sure if it was already discussed.
> 
> Not it wasn't.
> 
> > After all the CPU clocks, cluster, clock-gating, power domains are pretty much
> > related. So instead of having new binding for CPUFreq, I was wondering whether
> > we can extend the CPU topology binding information to include missing information.
> > Scheduler work anyway needs that information.
> >
> > Ref: Documentation/devicetree/bindings/arm/topology.txt
> >
> > Does that make sense ?
> 
> Yeah it does, but I am not sure what exactly the bindings should look then.
> So, the most basic step could be moving the new bindings to topology.txt
> and name clock-master to dvfs-master.
> 
> What else?

If we're going to model the hardware then the binding should not use the
CPU phandles in "clock-master" or "dvfs-master". The correct thing to
model for a given CPU is which clock consumes. It's not accurate to say
that one CPU is the "master", at least not in this context.

A previous approach tried to compare struct clk pointers, which is a bad
idea since those are just cookies and should not be deref'd by drivers.
However a similar approach would be to compare the phandle, right?

Regards,
Mike

> 
> If its going to be much controversial then we *can* go for just dvfs bindings
> for now and then update them later.
> 
> Doesn't make sense? :)