[PATCH 2/6] ARM: Tegra: Add CPU's OPPs for using cpufreq-cpu0 driver

Lucas Stach l.stach at pengutronix.de
Thu Aug 8 10:22:29 EDT 2013

Am Donnerstag, den 08.08.2013, 19:41 +0530 schrieb Viresh Kumar:
> On 8 August 2013 19:28, Lucas Stach <l.stach at pengutronix.de> wrote:
> > From what I learned those voltage levels are dependent on both the
> > Speedo and the process ID of the specific Tegra processor. So you really
> > get a two dimensional mapping table instead of a single OPP.
> > Also you can not scale the CPU voltage on it's own, but have to make
> > sure the core voltage isn't too far away from. Then core voltage also
> > depends on the operating states of engines like GR2D or even display.
> So if they depend on a certain type of SoC, which they should, then we
> can get these initialized from that SoC's dts/dtsi file instead of a common
> file.. And so that would resolve the issue you just reported.
You can certainly define the mapping table in DT where a specialized
Tegra cpufreq driver could read it in and then map frequency to voltage.
But that's a runtime decision, as Speedo and process ID are fuse values
and can not be represented in DT.

> Now I haven't proposed in the patch that we will change these voltage
> levels at all.. This is regulator specific code and would come into play
> only when regulators are registered for cpu.. Otherwise we will just
> play with frequency..
> Passing OPP instead of just list of frequencies is the generic way this
> is done now a days..

The problem with this is that the hardware description now associates
voltages with certain frequencies and even if they are not used by the
Linux driver they are plain wrong.

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