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

[Shawn Guo]

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.

Shawn

> so it
> may not be a big deal, but there is a small optimization I've
> discussed with a few other people that could avoid waking them up.  I
> suggest adding an extra pre-idle hook to the Tegra30 that is called by
> coupled cpuidle on the last cpu to go down.  It would return a cpumask
> of cpus that have been prepared for idle by guaranteeing that they
> will not wake up from an interrupt, and therefore don't need to be
> woken up for the transitions.  I haven't worked with a cpu that needs
> this optimization yet, so I haven't done it.
> 
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