Messages in this thread Patch in this message | | | Date | Wed, 31 Jul 2013 16:38:09 -0700 | From | Sören Brinkmann <> | Subject | Re: Enable arm_global_timer for Zynq brakes boot |
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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, Sören
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