Enable arm_global_timer for Zynq brakes boot

[Sören Brinkmann]

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