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

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

On Fri, May 01, 2015 at 11:45:06AM +0100, Lorenzo Pieralisi wrote:
> 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).
> 
> Ok, to start with, if we want the generic CPUidle driver to work on bL
> systems, we should get this patch merged:
> 
> http://www.spinics.net/lists/arm-kernel/msg412790.html

Thanks pointing out this.

> Architected timer is always lost on power down, unless we are talking
> about a logic retention state (or if we are talking about local timers
> that are not the architected ones). Anyway, with the patch above, different
> cpus can have different idle states, so different behaviours when it
> comes to the local timer behaviour. If, say, on a A53/A57 system, A53
> cpus lose the local timer on idle state entry and A57 cpus do not
> (that's a non-existing example though), those cpus will have different
> idle states so different local-timer-stop flags.

For A57, not sure if arch timer will be powered off if cpu has been
powered off.

>From A53's TRM figure 2-1 Cortex-A53 processor block diagram, the arch
timer is not within CPU power domain, so likey arch timer still will
work even cpu has been powered off (PDCPU/PDADVSIMD both have been off).
This looks like is not aligning w/t your upper description. Could u
confirm this understanding is right?

Thanks,
Leo Yan