Enable arm_global_timer for Zynq brakes boot

Daniel Lezcano daniel.lezcano at linaro.org
Wed Jul 31 16:49:06 EDT 2013

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 ?

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