On Wed, Jul 31, 2013 at 09:27:25AM +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.
>
> Hmm, interesting. Can you give the ouput of /proc/interrupts also with
> the global timer ?
Sure:
# cat /proc/interrupts
CPU0 CPU1
27: 14 1 GIC 27 gt
29: 841 843 GIC 29 twd
43: 0 0 GIC 43 ttc_clockevent
82: 563 0 GIC 82 xuartps
IPI0: 0 0 CPU wakeup interrupts
IPI1: 0 0 Timer broadcast interrupts
IPI2: 1266 1330 Rescheduling interrupts
IPI3: 0 0 Function call interrupts
IPI4: 34 59 Single function call interrupts
IPI5: 0 0 CPU stop interrupts
Err: 0
Sören
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