linux-kernel - Re: [PATCH v4 2/2] dt: power: st: Provide bindings for ST's OPPs

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Date:	Wed, 26 Aug 2015 13:06:28 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Stephen Boyd <sboyd@...eaurora.org>,
	Rob Herring <robherring2@...il.com>,
	Nishanth Menon <nm@...com>, kernel@...inux.com,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Rafael Wysocki <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sebastian Reichel <sre@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Arnd Bergmann <arnd.bergmann@...aro.org>,
	Ajit Pal Singh <ajitpal.singh@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 2/2] dt: power: st: Provide bindings for ST's OPPs

On Wed, 12 Aug 2015, Viresh Kumar wrote:

> On 11-08-15, 16:17, Lee Jones wrote:
> > This would work if we only had a single variable to contend with, but
> > what I showed you in my previous example is that we have 3 variables
> > to consider; cut (version), pcode and substrate.
> > 
> > Using the two (simple) examples I provided, how would your suggestion
> > look in our case?
> 
> So the solution I gave is for picking the microvolt based on pcode.
> The other two (cut, substrate) aren't about picking microvolt, but if
> the OPP is available or not. Right?

'pcode', 'cut' and 'substrate' all determine whether a given set of
OPPs an be used on the running platform.  I do not believe that you
can differentiate between them. 

> If these terms are generic enough, then we can add something similar
> to what you have added..

If it makes it easier, you can treat them as version numbers 2.2.1
<pcode.cut.substrate>, but I don't see how this can help.  Obviously
this becomes more difficult when you add wild cards to the OPPs, where
a particular OPP would be suitable for all cuts for example.

If you still think you can come up with a generic method to lay out
CPUFreq OPP nodes that will satisfy all vendors and not be a mass of
10's of separate nodes, then great.  Again, I'm struggling to see how
that might be possible.

What I believe we shouldn't do, is have this blocked forever for the
sake of adding a couple of vendor properties however.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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