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SubjectRe: Enable arm_global_timer for Zynq brakes boot
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 ?

> next_event: 108080000000 nsecs
> set_next_event: gt_clockevent_set_next_event
> set_mode: gt_clockevent_set_mode
> event_handler: tick_handle_oneshot_broadcast
> retries: 0
>
> tick_broadcast_mask: 00000001
> tick_broadcast_oneshot_mask: 00000000
>
> Tick Device: mode: 1
> Per CPU device: 0
> Clock Event Device: local_timer
> max_delta_ns: 12884902005
> min_delta_ns: 1000
> mult: 715827876
> shift: 31
> mode: 3
> next_event: 106900000000 nsecs
> set_next_event: twd_set_next_event
> set_mode: twd_set_mode
> event_handler: hrtimer_interrupt
> retries: 0
>
> # cat /proc/interrupts
> CPU0
> 27: 252 GIC 27 gt
> 29: 626 GIC 29 twd
> 43: 0 GIC 43 ttc_clockevent
> 82: 410 GIC 82 xuartps
> IPI0: 0 CPU wakeup interrupts
> IPI1: 0 Timer broadcast interrupts
> IPI2: 0 Rescheduling interrupts
> IPI3: 0 Function call interrupts
> IPI4: 0 Single function call interrupts
> IPI5: 0 CPU stop interrupts
> Err: 0
>
>
> Sören
>
>


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