linux-kernel - Re: [PATCH 01/13] clk: tegra: Add binding for the Tegra124 DFLL clocksource

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Date:	Mon, 14 Jul 2014 10:38:56 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Tuomas Tynkkynen <ttynkkynen@...dia.com>
Cc:	Andrew Bresticker <abrestic@...omium.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Mike Turquette <mturquette@...aro.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH 01/13] clk: tegra: Add binding for the Tegra124 DFLL
 clocksource

On Fri, Jul 11, 2014 at 08:21:27PM +0300, Tuomas Tynkkynen wrote:
> 
> 
> On 11/07/14 20:08, Andrew Bresticker wrote:
> >On Fri, Jul 11, 2014 at 9:48 AM, Tuomas Tynkkynen <ttynkkynen@...dia.com> wrote:
> >>
> >>
> >>On 11/07/14 19:28, Andrew Bresticker wrote:
> >>>
> >>>On Thu, Jul 10, 2014 at 2:42 PM, Tuomas Tynkkynen <ttynkkynen@...dia.com>
> >>>wrote:
> >>>>
> >>>>The DFLL is the main clocksource for the fast CPU cluster on Tegra124
> >>>>and also provides automatic CPU rail voltage scaling as well. The DFLL
> >>>>is a separate IP block from the usual Tegra124 clock-and-reset
> >>>>controller, so it gets its own node in the device tree.
> >>>
> >>>
> >>>>diff --git
> >>>>a/Documentation/devicetree/bindings/clock/nvidia,tegra124-dfll.txt
> >>>>b/Documentation/devicetree/bindings/clock/nvidia,tegra124-dfll.txt
> >>>
> >>>
> >>>>+- nvidia,pmic-voltage-table: Array of 2-tuples.  Each entry should have
> >>>>the
> >>>>+  form <register-value voltage-in-uV>, indicating the register value
> >>>>that
> >>>>+  needs to be programmed to the PMIC for changing the VDD_CPU voltage to
> >>>>+  the specified voltage. The table must be in ascending order by the
> >>>>voltage.
> >>>
> >>>
> >>>Instead of listing the register values for each voltage in the DT,
> >>>can't you use regulator_list_voltage() to create this map?
> >>>
> >>
> >>I don't see a way to get the register values that way, unless we assume that
> >>the mapping is linear and doesn't have holes.
> >
> >Hmm... I guess if you don't assume it's linear and continuous you'd
> >have to iterate over all 256 selectors.
> >
> 
> I don't think we can assume that each selector maps to a concrete register
> value, though I'm not sure. include/linux/regulator/driver.h documents for
> @list_voltage "Selectors range from zero to one less
> regulator_desc.n_voltages." but maybe the consumer API could take different
> values.

I don't think the regulator API makes any guarantees that the selector
corresponds to a register value. Adding Mark Brown, maybe he can help
figure out the best way to do this.

Thierry

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