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Date: Wed, 31 Jul 2013 16:38:09 -0700
From: Sören Brinkmann <soren.brinkmann@...inx.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
CC: Stephen Boyd <sboyd@...eaurora.org>,
John Stultz <john.stultz@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>,
Stuart Menefy <stuart.menefy@...com>,
Russell King <linux@....linux.org.uk>,
Michal Simek <michal.simek@...inx.com>,
<linux-kernel@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Enable arm_global_timer for Zynq brakes boot
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
View attachment "boot.log" of type "text/plain" (25156 bytes)
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