[PATCH 7/7] ARM: tegra30: cpuidle: add LP2 driver for CPU0

[Shawn Guo]

On Fri, Oct 12, 2012 at 04:24:24PM +0800, Joseph Lo wrote:
> On Fri, 2012-10-12 at 15:54 +0800, Shawn Guo wrote:
> > On Thu, Oct 11, 2012 at 09:48:45AM -0700, Colin Cross wrote:
> > > As is, coupled cpuidle will work on Tegra30, but it will unnecessarily
> > > wake up the secondary cpus during the transitions to off and back on
> > > again.  Those cpus will immediately go back to single-cpu LP2,
> > 
> > I'm sure coupled cpuidle will work like that.  We have the following
> > code at the end of  cpuidle_enter_state_coupled() to wait until all
> > coupled cpus have exited idle.
> > 
> >         while (!cpuidle_coupled_no_cpus_ready(coupled))
> >                 cpu_relax();
> > 
> > The cpu woken up during the transitions will just loop there until all
> > other 3 cpus exit from idle function.
> > 
> 
> Did this a good idea if the CPU was been woken up from an interrupt but
> it still needed to wait all other CPUs been woken up then it could
> handle the interrupt?
> 
This is how coupled cpuidle gets implemented right now.  And that's
why I see RCU stall warning reported on that cpu when I tried coupled
cpuidle on imx6q (CA9 Quad).

Shawn