Re: [PATCH V2] cpufreq: ARM big LITTLE: Add generic cpufreq driverand its DT glue

From: Guennadi Liakhovetski
Date: Fri Mar 08 2013 - 01:11:59 EST

Hi Viresh

On Fri, 8 Mar 2013, Viresh Kumar wrote:

> On 8 March 2013 05:56, Guennadi Liakhovetski <g.liakhovetski@xxxxxx> wrote:
> > I like generic drivers :)
> Me too :)
> > cpufreq-cpu0 is yet another such generic
> > (cpufreq) driver. Now, comparing the functionality of the two:
> Great!!
> > we see, that this driver "only" switches CPU clock frequencies. Whereas
> > the cpufreq-cpu0 driver also manipulates a regulator (if available)
> > directly. I understand, power-saving is also an important consideration
> > for big.LITTLE systems. So, I presume, you plan to implement voltage
> > switching in cpufreq notifiers?
> So the platform on which we are currently testing these is ARM TC2 Soc
> and this switching is done by the firmware instead. And so didn't went
> for regulator hookups initially.. Obviously in future regulator hookups would
> find some space in this driver but not required for now.
> > Now, my question is: is this (notifier)
> > actually the preferred method and the cpufreq-cpu0 driver is doing it
> > "wrongly?"
> What notifiers are you talking about? I believe using the regulator framework
> is the right way of doing this. And that would be part of this code later on.

Also in your driver you're doing

cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);
cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);

So, theoretically you could install such notifiers to adjust CPU voltages
(using regulators too). But adding regulator calls directly to the driver
would make it consistent with cpufreq-cpu0.c, so, if this doesn't violate
any concepts, I think, it would be good to add those when suitable systems

Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
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