Messages in this thread | | | Date | Thu, 1 Aug 2013 10:43:58 -0700 | From | Sören Brinkmann <> | Subject | Re: Enable arm_global_timer for Zynq brakes boot |
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On Thu, Aug 01, 2013 at 07:29:12PM +0200, Daniel Lezcano wrote: > On 08/01/2013 01:38 AM, Sören Brinkmann wrote: > > On Thu, Aug 01, 2013 at 01:01:27AM +0200, Daniel Lezcano wrote: > >> On 08/01/2013 12:18 AM, Sören Brinkmann wrote: > >>> On Wed, Jul 31, 2013 at 11:08:51PM +0200, Daniel Lezcano wrote: > >>>> On 07/31/2013 10:58 PM, Sören Brinkmann wrote: > >>>>> On Wed, Jul 31, 2013 at 10:49:06PM +0200, Daniel Lezcano wrote: > >>>>>> On 07/31/2013 12:34 AM, Sören Brinkmann wrote: > >>>>>>> On Tue, Jul 30, 2013 at 10:47:15AM +0200, Daniel Lezcano wrote: > >>>>>>>> On 07/30/2013 02:03 AM, Sören Brinkmann wrote: > >>>>>>>>> Hi Daniel, > >>>>>>>>> > >>>>>>>>> On Mon, Jul 29, 2013 at 02:51:49PM +0200, Daniel Lezcano wrote: > >>>>>>>>> (snip) > >>>>>>>>>> > >>>>>>>>>> the CPUIDLE_FLAG_TIMER_STOP flag tells the cpuidle framework the local > >>>>>>>>>> timer will be stopped when entering to the idle state. In this case, the > >>>>>>>>>> cpuidle framework will call clockevents_notify(ENTER) and switches to a > >>>>>>>>>> broadcast timer and will call clockevents_notify(EXIT) when exiting the > >>>>>>>>>> idle state, switching the local timer back in use. > >>>>>>>>> > >>>>>>>>> I've been thinking about this, trying to understand how this makes my > >>>>>>>>> boot attempts on Zynq hang. IIUC, the wrongly provided TIMER_STOP flag > >>>>>>>>> would make the timer core switch to a broadcast device even though it > >>>>>>>>> wouldn't be necessary. But shouldn't it still work? It sounds like we do > >>>>>>>>> something useless, but nothing wrong in a sense that it should result in > >>>>>>>>> breakage. I guess I'm missing something obvious. This timer system will > >>>>>>>>> always remain a mystery to me. > >>>>>>>>> > >>>>>>>>> Actually this more or less leads to the question: What is this > >>>>>>>>> 'broadcast timer'. I guess that is some clockevent device which is > >>>>>>>>> common to all cores? (that would be the cadence_ttc for Zynq). Is the > >>>>>>>>> hang pointing to some issue with that driver? > >>>>>>>> > >>>>>>>> If you look at the /proc/timer_list, which timer is used for broadcasting ? > >>>>>>> > >>>>>>> So, the correct run results (full output attached). > >>>>>>> > >>>>>>> The vanilla kernel uses the twd timers as local timers and the TTC as > >>>>>>> broadcast device: > >>>>>>> Tick Device: mode: 1 > >>>>>>> Broadcast device > >>>>>>> Clock Event Device: ttc_clockevent > >>>>>>> > >>>>>>> When I remove the offending CPUIDLE flag and add the DT fragment to > >>>>>>> enable the global timer, the twd timers are still used as local timers > >>>>>>> and the broadcast device is the global timer: > >>>>>>> Tick Device: mode: 1 > >>>>>>> Broadcast device > >>>>>>> Clock Event Device: arm_global_timer > >>>>>>> > >>>>>>> Again, since boot hangs in the actually broken case, I don't see way to > >>>>>>> obtain this information for that case. > >>>>>> > >>>>>> Can't you use the maxcpus=1 option to ensure the system to boot up ? > >>>>> > >>>>> Right, that works. I forgot about that option after you mentioned, that > >>>>> it is most likely not that useful. > >>>>> > >>>>> Anyway, this are those sysfs files with an unmodified cpuidle driver and > >>>>> the gt enabled and having maxcpus=1 set. > >>>>> > >>>>> /proc/timer_list: > >>>>> Tick Device: mode: 1 > >>>>> Broadcast device > >>>>> Clock Event Device: arm_global_timer > >>>>> max_delta_ns: 12884902005 > >>>>> min_delta_ns: 1000 > >>>>> mult: 715827876 > >>>>> shift: 31 > >>>>> mode: 3 > >>>> > >>>> Here the mode is 3 (CLOCK_EVT_MODE_ONESHOT) > >>>> > >>>> The previous timer_list output you gave me when removing the offending > >>>> cpuidle flag, it was 1 (CLOCK_EVT_MODE_SHUTDOWN). > >>>> > >>>> Is it possible you try to get this output again right after onlining the > >>>> cpu1 in order to check if the broadcast device switches to SHUTDOWN ? > >>> > >>> How do I do that? I tried to online CPU1 after booting with maxcpus=1 > >>> and that didn't end well: > >>> # echo 1 > online && cat /proc/timer_list > >> > >> Hmm, I was hoping to have a small delay before the kernel hangs but > >> apparently this is not the case... :( > >> > >> I suspect the global timer is shutdown at one moment but I don't > >> understand why and when. > >> > >> Can you add a stack trace in the "clockevents_shutdown" function with > >> the clockevent device name ? Perhaps, we may see at boot time an > >> interesting trace when it hangs. > > > > I did this change: > > diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c > > index 38959c8..3ab11c1 100644 > > --- a/kernel/time/clockevents.c > > +++ b/kernel/time/clockevents.c > > @@ -92,6 +92,8 @@ void clockevents_set_mode(struct clock_event_device *dev, > > */ > > void clockevents_shutdown(struct clock_event_device *dev) > > { > > + pr_info("ce->name:%s\n", dev->name); > > + dump_stack(); > > clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN); > > dev->next_event.tv64 = KTIME_MAX; > > } > > > > It is hit a few times during boot, so I attach a full boot log. I really > > don't know what to look for, but I hope you can spot something in it. I > > really appreciate you taking the time. > > Thanks for the traces.
Sure.
> > If you try without the ttc_clockevent configured in the kernel (but with > twd and gt), does it boot ?
Absence of the TTC doesn't seem to make any difference. It hangs at the same location.
Thanks, Sören
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