[PATCH] ARM: tegra: cpuidle: use CPUIDLE_FLAG_TIMER_STOP flag

[josephl@nvidia.com (Joseph Lo)]

On Thu, 2013-07-18 at 20:41 +0800, Daniel Lezcano wrote:
> On 07/18/2013 01:08 PM, Joseph Lo wrote:
> > On Thu, 2013-07-18 at 04:31 +0800, Stephen Warren wrote:
> >> On 07/17/2013 04:15 AM, Joseph Lo wrote:
> >>> On Wed, 2013-07-17 at 03:51 +0800, Stephen Warren wrote:
> >>>> On 07/16/2013 05:17 AM, Joseph Lo wrote:
> >>>>> On Tue, 2013-07-16 at 02:04 +0800, Stephen Warren wrote:
> >>>>>> On 06/25/2013 03:23 AM, Joseph Lo wrote:
> >>>>>>> Use the CPUIDLE_FLAG_TIMER_STOP and let the cpuidle framework
> >>>>>>> to handle the CLOCK_EVT_NOTIFY_BROADCAST_ENTER/EXIT when entering
> >>>>>>> this state.
> >> ... [ discussion of issues with Joesph's patches applied]
> >>>
> >>> OK. I did more stress tests last night and today. I found it cause by
> >>> the patch "ARM: tegra: cpuidle: use CPUIDLE_FLAG_TIMER_STOP flag" and
> >>> only impact the Tegra20 platform. The hot plug regression seems due to
> >>> this patch. After dropping this patch on top of v3.11-rc1, the Tegra20
> >>> can back to normal.
> >>>
> >>> And the hop plug and suspend stress test can pass on Tegra30/114 too.
> >>>
> >>> Can the other two patch series for Tegra114 to support CPU idle power
> >>> down mode and system suspend still moving forward, not be blocked by
> >>> this patch?
> >>>
> >>> Looks the CPUIDLE_FLAG_TIMER_STOP flag still cause some other issue for
> >>> hot plug on Tegra20, I will continue to check this. You can just drop
> >>> this patch.
> >>
> >> OK, if I drop that patch, then everything on Tegra20 and Tegra30 seems
> >> fine again.
> >>
> >> However, I've found some new and exciting issue on Tegra114!
> >>
> >> With unmodified v3.11-rc1, I can do the following without issue:
> >>
> >> * Unplug/replug CPUs, so that I had all combinations of CPU 1, 2, 3
> >> plugged/unpplugged (with CPU 0 always plugged).
> >>
> >> * Unplug/replug CPUs, so that I had all combinations of CPU 0, 1, 2, 3
> >> plugged/unpplugged (with the obvious exception of never having all CPUs
> >> unplugged).
> >>
> >> However, if I try this with your Tegra114 cpuidle and suspend patches
> >> applied, I see the following issues:
> >>
> >> 1) If I boot, unplug CPU 0, then replug CPU 0, the system immediately
> >> hard-hangs.
> >>
> > Sorry, I didn't apply the hotplug stress test on CPU0 too much. Because
> > all of our use cases and stress tests are focused on secondary CPUs
> > only.
> >
> > After doing some tests, here is my summary. This issue happens after we
> > support CPU idle power-down mode and relates to PMC or flow controller I
> > believe.
> >
> > i) on top of v3.11-rc1 (only support WFI in CPU idle)
> > When hot unplug CPU0, the PMC can power gate and put it into reset
> > state. This is what I expect and also true on all the other secondary
> > CPUs. The flow controller can maintain the CPU power state machine as
> > what we want.
> >
> > ii) on top of v3.11-rc1 + CPU idle power down mode support
> > a) I saw most of the time the CPU0,1,2,3 were in power down and reset
> > status. That means the idle power down mode works fine.
> >
> > b) Testing with the CPU hotplug stress test with the secondary CPUs (not
> > include CPU0), the result is good too.
> >
> > c) Testing hot plug on CPU0 with CPUIDLE_FLAG_TIMER_STOP apply or not
> > apply (Note 1), the result shows not good to me. The CPU0 have already
> > gone into WFI and the flow controller is set as WAITFOREVENT mode. But
> > the PMC always can't power gate CPU0 and sometimes can put it into
> > reset, but sometimes can't. That's why you can see it hanging after
> > unplug CPU0 sometimes.
> 
> Are sure coupled idle state support hotplug and especially the cpu0
> hotplug ?

Tegra114 didn't use coupled idle framework.