linux-kernel - Re: Enable arm_global_timer for Zynq brakes boot

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Message-ID: <52090B43.9090000@codeaurora.org>
Date:	Mon, 12 Aug 2013 09:20:19 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
CC:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	srinivas.kandagatla@...com, Russell King <linux@....linux.org.uk>,
	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, Stuart Menefy <stuart.menefy@...com>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Enable arm_global_timer for Zynq brakes boot

On 08/12/13 09:03, Sören Brinkmann wrote:
> On Fri, Aug 09, 2013 at 10:27:57AM -0700, Stephen Boyd wrote:
>> On 08/09, Daniel Lezcano wrote:
>>> yes, but at least the broadcast mechanism should send an IPI to cpu0 to
>>> wake it up, no ? As Stephen stated this kind of configuration should has
>>> never been tested before so the tick broadcast code is not handling this
>>> case properly IMHO.
>>>
>> If you have a per-cpu tick device that isn't suffering from
>> FEAT_C3_STOP why wouldn't you use that for the tick versus a
>> per-cpu tick device that has FEAT_C3_STOP? It sounds like there
>> is a bug in the preference logic or you should boost the rating
>> of the arm global timer above the twd. Does this patch help? It
>> should make the arm global timer the tick device and whatever the
>> cadence timer you have into the broadcast device.
> I finally got to test your patch. Unfortunately, it makes the system
> hang even earlier:

Sorry it had a bug depending on the registration order. Can you try this
one (tabs are probably spaces, sorry)? I will go read through this
thread to see if we already covered the registration order.

---8<----
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 218bcb5..d3539e5 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -77,6 +77,9 @@ static bool tick_check_broadcast_device(struct clock_event_device *curdev,
            !(newdev->features & CLOCK_EVT_FEAT_ONESHOT))
                return false;
 
+       if (cpumask_equal(newdev->cpumask, cpumask_of(smp_processor_id())))
+               return false;
+
        return !curdev || newdev->rating > curdev->rating;
 }
 
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 64522ec..dd08f3b 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -244,12 +244,22 @@ static bool tick_check_preferred(struct clock_event_device *curdev,
                        return false;
        }
 
+       if (!curdev)
+               return true;
+
+       /* Always prefer a tick device that doesn't suffer from FEAT_C3STOP */
+       if (!(newdev->features & CLOCK_EVT_FEAT_C3STOP) &&
+            (curdev->features & CLOCK_EVT_FEAT_C3STOP))
+               return true;
+       if ((newdev->features & CLOCK_EVT_FEAT_C3STOP) &&
+           !(curdev->features & CLOCK_EVT_FEAT_C3STOP))
+               return false;
+
        /*
         * Use the higher rated one, but prefer a CPU local device with a lower
         * rating than a non-CPU local device
         */
-       return !curdev ||
-               newdev->rating > curdev->rating ||
+       return newdev->rating > curdev->rating ||
               !cpumask_equal(curdev->cpumask, newdev->cpumask);
 }
 


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