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Message-ID: <51F97CE3.9030306@linaro.org> Date: Wed, 31 Jul 2013 23:08:51 +0200 From: Daniel Lezcano <daniel.lezcano@...aro.org> To: Sören Brinkmann <soren.brinkmann@...inx.com> CC: Stephen Boyd <sboyd@...eaurora.org>, John Stultz <john.stultz@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, Stuart Menefy <stuart.menefy@...com>, Russell King <linux@....linux.org.uk>, Michal Simek <michal.simek@...inx.com>, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org Subject: Re: 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 > > -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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