linux-kernel - Re: [PATCH 01/16] PM / OPP: Add 'supply-names' binding

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Message-ID: <20151022163942.GX8232@sirena.org.uk>
Date:	Fri, 23 Oct 2015 01:39:42 +0900
From:	Mark Brown <broonie@...nel.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Stephen Boyd <sboyd@...eaurora.org>, Rob Herring <robh@...nel.org>,
	Rafael Wysocki <rjw@...ysocki.net>, nm@...com,
	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	rob.herring@...aro.org, lee.jones@...aro.org,
	devicetree@...r.kernel.org,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	open list <linux-kernel@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 01/16] PM / OPP: Add 'supply-names' binding

On Sat, Oct 17, 2015 at 09:40:55AM +0530, Viresh Kumar wrote:

> Okay here is the problem statement:

> We have two supplies for a device and the device node will have
> something like:

> name1-supply = <&supply1>;
> name2-supply = <&supply2>;

> And the OPP node needs to have voltages for both of them:

> opp-microvolt = <X1 Y1 Z1>, <X2 Y2 Z2>;

> Where XYZ(1) are for supply1 and XYZ(2) are for supply2.

> Now we need to identify the supplies for which the values are present
> here and their order as well. How do we do that?

> The way I am suggesting is to add a property in opp node which will
> keep "name1" and "name2" in it.

When we start doing this we also start having to worry about things like
the sequencing of the updates between the various supplies and end up in
full on power sequencing (or at least baking some sequencing into the DT
which will doubtless need extending at some point).  I'm not sure that's
a place we want to end up just yet, I think it's safer to just have a
little bit of code in the kernel that glues things together in the cases
where this is needed.  

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