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    SubjectRe: timers & suspend
    On 07/03/2014 07:40 PM, Sören Brinkmann wrote:
    > On Thu, 2014-07-03 at 07:26PM +0200, Daniel Lezcano wrote:
    >> On 07/03/2014 06:09 PM, Sören Brinkmann wrote:
    >>> On Thu, 2014-07-03 at 02:21PM +0200, Daniel Lezcano wrote:
    >>>> On 06/30/2014 08:39 PM, Sören Brinkmann wrote:
    >>>>> Hi,
    >>>>>
    >>>>> I'm currently working on suspend for Zynq and try to track down some
    >>>>> spurious wakes. It looks like the spurious wakes are caused by timers,
    >>>>> hence I was wondering whether there are any special requirements for
    >>>>> timer drivers when it comes to suspend support or if I just missed
    >>>>> something.
    >>>>>
    >>>>> Zynq sets the 'IRQCHIP_MASK_ON_SUSPEND' flag, which should mask all
    >>>>> interrupts but the wake source. Reading through kernel/irq/pm.c
    >>>>> indicates, that timer interrupts get some special treatment though.
    >>>>> Therefore I implemented some suspend/resume callbacks for the
    >>>>> cadence_ttc which disable and clear the timer's interrupts when going
    >>>>> into suspend. That seems to mitigate the issue quite a bit, but I still
    >>>>> saw spurious wakes - just a lot less often.
    >>>>> Digging a little deeper revealed, the spurious wakes are caused by the
    >>>>> ARM's smp_twd timer now. Given that that driver is probably used by a few
    >>>>> more ARM platforms, I get the feeling that I'm missing something.
    >>>>
    >>>> Do you receive any interrupt from the cadence_ttc ? (/proc/interrupts)
    >>>>
    >>>> That's funny because I realize that you cadence ttc timer is never
    >>>> used as there are the architected timers. The cadence ttc would be
    >>>> only useful if there were an idle state powering down the smp_twd
    >>>> timers but it is not the case on this board, IIUC.
    >>> Yes they are used. They TTC is the only broadcast capable timer for
    >>> Zynq. In my experience, I can not even boot without it (may have
    >>> dependencies on CPUidle or something).
    >>
    >> Actually the cpuidle driver is wrong. It assumes the state #1 will
    >> power off the different cores with their architected timers and then
    >> switch to the broadcast timer. But this one is not needed as we
    >> don't power down the core with the twd timers, so no need to switch
    >> to a backup timer device.
    >>
    >> The implementation of the DDR self refresh idle state (incoming
    >> patchset) removes the cpu_pm notifiers + the flag TIMER_STOP. The
    >> result is 0 interrupts for ttc cadence timer. I removed in the dts
    >> the cadence ttc and my board booted without problem (it is a zynq
    >> 702).
    >>
    >> Except I missed something, the cadence ttc is actually not used at all.
    > I tested on the current master branch. I see TTC interrupts on CPU0 and
    > timer_list shows the TTC to be the broadcast device. Removing the TTC
    > nodes from my DT results in boot hanging - shortly after cpuidle is
    > started.
    >
    > Removing cpuidle from my kernel makes the system boot. And it has no
    > broadcast device anymore.

    You can safely remove the CPUIDLE_FLAG_TIMER_STOP in the cpuidle drivers
    and I am pretty sure it will boot without problem.

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