[PATCH] arm64: dts: Add idle-states for Juno

[leo.yan@linaro.org (Leo Yan)]

On Fri, May 01, 2015 at 11:22:31AM +0100, Jon Medhurst (Tixy) wrote:
> On Fri, 2015-05-01 at 09:55 +0800, Leo Yan wrote:
> [...]
> > >  arch/arm64/boot/dts/arm/juno.dts | 28 ++++++++++++++++++++++++++++
> > >  1 file changed, 28 insertions(+)
> > > 
> > > diff --git a/arch/arm64/boot/dts/arm/juno.dts b/arch/arm64/boot/dts/arm/juno.dts
> > > index 133ee59..7a9a449 100644
> > > --- a/arch/arm64/boot/dts/arm/juno.dts
> > > +++ b/arch/arm64/boot/dts/arm/juno.dts
> > > @@ -34,12 +34,35 @@
> > >  		#address-cells = <2>;
> > >  		#size-cells = <0>;
> > >  
> > > +		idle-states {
> > > +			entry-method = "arm,psci";
> > > +
> > > +			CPU_SLEEP_0: cpu-sleep-0 {
> > > +				compatible = "arm,idle-state";
> > > +				arm,psci-suspend-param = <0x0010000>;
> > > +				local-timer-stop;
> > 
> > Just want to figure out the best way for big.LITTLE system; so have
> > one question: CA53 and CA57 have different power domain for arch
> > timer, right?
> 
> I'm not sure of the answer to that. The documentation I have does seem
> to state the timer is lost on cluster power down, which would imply that
> it's not when just powering down a cpu, but I'm not at all clear on the
> matter.
> 
> >  If this is the case, should we define two kinds of cpu
> > sleep states, one of them will not migrate to broadcast timer and
> > keep using arch timer after cpu has been powered down?
> 
> Do you mean that if the local timer is not lost (and so we should not
> have local-timer-stop above), then we should have another identical idle
> state except that it _does_ specify local-timer-stop to force the
> broadcast time to be used? If so, would that second state ever be more
> power efficient than the first? (I don't know the answer to that, this
> whole area is pretty new to me).

Yes, the second state will have better power efficient. But if the
arch timer can keep working after the cpu is powered off, we also
can get benefit for cpuidle's latency, this is because s/w don't need
migrate the cpu timers to broad cast timer list anymore.

Thanks,
Leo Yan