linux-kernel - Re: [RFC PATCH 3/6] PM / Voltagedomain: introduce voltage domain driver support

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Date:	Mon, 3 Mar 2014 11:54:26 +0800
From:	Mark Brown <broonie@...nel.org>
To:	Nishanth Menon <nm@...com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Mike Turquette <mturquette@...aro.org>,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-omap@...r.kernel.org
Subject: Re: [RFC PATCH 3/6] PM / Voltagedomain: introduce voltage domain
 driver support

On Mon, Feb 24, 2014 at 08:38:07AM -0600, Nishanth Menon wrote:

> Intent here is to allow drivers such as cpufreq-cpu0 to be reused on
> platforms such as TI's OMAP derivatives, and other SoCs which differ
> only by the sequence involved in voltage scale operations. So, this
> patch provides a framework for registering the underlying
> implementation of the SoC specific voltage change methodology.

That bit is clear, what's very opaque from the code is how this is going
to be accomplished.

> Overall the sequence takes place after this patch is as follows:
> a) voltage domain drivers such as those of TI or others register with
> voltage domain with devm_voltdm_register.
> b) cpufreq-cpu0/devfreq drivers:
> of_pm_voltdm_notifier_register(introduced as part of patch #1) to
> register notifiers around clk of interest. This request is linked to
> the specific voltage domain using phandle in device tree.
> c) when cpufreq-cpu0/devfreq does a clk_set_rate, the common clock
> framework triggers notifiers in voltage domain core which in turn,
> invokes the corresponding handlers for the voltage domain driver
> ensuring the right dvfs sequence specific to the SoC is triggered.

So the first question I have here is what happens if multiple clocks
need to be updated in lock step - if we're only triggering off clock
notifiers that seems tricky.  The other thing here is that the fact that
your API is "of_" suggests that it is in fact linked very srongly to DT
- it'd be good to split out the layers to make sure things make sense
standalone, the DT helpers are obviously good but the API should be able
to stand separately.

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