[PATCH V4 5/5] ARM: tegra20: cpuidle: apply coupled cpuidle for powered-down mode

[josephl@nvidia.com (Joseph Lo)]

On Thu, 2013-01-17 at 05:31 +0800, Stephen Warren wrote:
> On 01/16/2013 11:55 AM, Colin Cross wrote:
> > On Wed, Jan 16, 2013 at 12:11 AM, Joseph Lo <josephl@nvidia.com> wrote:
> >> The "powered-down" cpuidle mode of Tegra20 needs the CPU0 be the last one
> >> core to go into this mode before other core. The coupled cpuidle framework
> >> can help to sync the MPCore to coupled state then go into "powered-down"
> >> idle mode together. The driver can just assume the MPCore come into
> >> "powered-down" mode at the same time. No need to take care if the CPU_0
> >> goes into this mode along and only can put it into safe idle mode (WFI).
> >>
> >> The powered-down state of Tegra20 requires power gating both CPU cores.
> >> When the secondary CPU requests to enter powered-down state, it saves
> >> its own contexts and then enters WFI for waiting CPU0 in the same state.
> >> When the CPU0 requests powered-down state, it attempts to put the secondary
> >> CPU into reset to prevent it from waking up. Then power down both CPUs
> >> together and power off the cpu rail.
> >>
> >> Be aware of that, you may see the legacy power state "LP2" in the code
> 
> Colin, since you only raised a few small issues on this series, does
> that mean you're OK with it once those issues are fixed?
> 
> Joseph, we'll be merging Tegra114 in the near future. How will this
> patch series affect Tegra114? Will the cpuidle driver simply fail to
> register on Tegra114 (which would be fine until we explicitly add
> support), or would we need to disable cpuidle in Kconfig to get a
> working Tegra114 kernel. Does this patch series affect the answer to the
> previous question? Thanks.
> 
Stephen,

This patch series won't affect Tegra114. I think I need to add a simple
cpuidle driver for Tegra114 to support just WFI state first.

And I am going do some re-works about CPUs and cluster power status sync
functions that be introduced recently[1] for CPU hotplug, idle and
secondary booting in Tegra tree. I hope I can hide all the power related
function behind that and make the CPU idle driver be more generic for
all Tegra series.

Before that re-works, I will still keep upstream the platform suspend
function for Tegra.
(If I am not in the right direction, please pull me back.)

Thanks,
Joseph

[1]: https://patchwork.kernel.org/patch/1957891/
     https://patchwork.kernel.org/patch/1957951/
     (pretty good job by Nicolas and Dave)