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

[lorenzo.pieralisi@arm.com (Lorenzo Pieralisi)]

On Fri, May 01, 2015 at 10:02:02AM +0100, Catalin Marinas wrote:
> On Thu, Apr 30, 2015 at 06:17:01PM +0100, Lorenzo Pieralisi wrote:
> > On Thu, Apr 30, 2015 at 05:40:35PM +0100, Jon Medhurst (Tixy) wrote:
> > > On Thu, 2015-04-30 at 17:00 +0100, Sudeep Holla wrote:
> > > > On 30/04/15 14:57, Jon Medhurst (Tixy) wrote:
> > > > > From: Jon Medhurst <tixy@linaro.org>
> > > > >
> > > > > Signed-off-by: Jon Medhurst <tixy@linaro.org>
> > > > > ---
> > > > >
> > > > > These have been kicking around out of tree for ages, any reason they
> > > > > shouldn't be in mainline?
> > > > 
> > > > One possible reason could be that these values are not tuned(e.g.
> > > > latency values, can they be same for both clusters ?)
> > > 
> > > I thought that both clusters being the same was questionable.
> > > 
> > > >  Though these
> > > > reasons are not blocking and this patch will not cause any
> > > > functionality break even if is merged as is.
> > > 
> > > My main purpose with trying to get this merged is so that people using
> > > Juno for general testing and validation will actually have cpuidle
> > > running and so potentially find more bugs.
> > 
> > I am reluctant to enable idle states in the default Juno dts, they
> > will affect latencies and performance tests significantly.
> 
> OTOH, I guess they will improve the power benchmarks. IMO, we should
> place in the DT whatever the hardware and firmware supports. It's up to
> those doing benchmarks to disable CPU suspend.

I am ok with DT defining whatever HW and FW support, the question is
whether we want CPUidle (and CPUfreq) enabled by default in the
defconfig then.

This will certainly trigger mainline regressions from a latency/performance
standpoint (true, some tests disable idle states by default ie cyclic
test), unless we disable CPUidle via command line parameter or we
force people carrying out tests to disable idle states through sysfs knobs.

Lorenzo