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

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Date:	Tue, 15 Sep 2015 08:17:47 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Rob Herring <robh@...nel.org>
Cc:	Rafael Wysocki <rjw@...ysocki.net>, nm@...com,
	sboyd@...eaurora.org, linaro-kernel@...ts.linaro.org,
	linux-pm@...r.kernel.org, rob.herring@...aro.org,
	lee.jones@...aro.org, Mark Brown <broonie@...nel.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 14-09-15, 15:22, Rob Herring wrote:
> What if we have a 2nd device and supply rail? For example, what if the
> L2$ has a separate rail from the cores but is linked to the OPPs.

Right, so that is the case with the Mediatek SoC as well, AFAIR. How
do we plan to treat L2 devices? For example, in the mediatek cpufreq
driver, they change L2's supplies together with CPUs.

One way to get that done, with such very closely bound devices is to
add two regulators:

cpu-supply = ...;
l2-supply = ...;

And then a property in OPP table:

supply-name = "cpu", "l2";

And maybe fix the order in which the supplies which be updated, based
on the order in which entries are present in the above property.

Any other way you suggest for doing that ?

> Remind me of when do we have multiple regulators for a cpu?

I haven't seen that yet, but its more like what I explained above.
i.e. one for the CPU and other one for the L2 cache.

But, these bindings do apply for other devices as well, where it
should be very much possible.

-- 
viresh
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