On 07/31/2013 12:34 AM, S?ren Brinkmann wrote:

On Tue, Jul 30, 2013 at 10:47:15AM +0200, Daniel Lezcano wrote:

quoted

On 07/30/2013 02:03 AM, S?ren Brinkmann wrote:

quoted

Hi Daniel,

On Mon, Jul 29, 2013 at 02:51:49PM +0200, Daniel Lezcano wrote:
(snip)

quoted

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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