Hi Thomas,
On Thu, Sep 12, 2013 at 10:30:15PM +0200, Thomas Gleixner wrote:
> On Thu, 12 Sep 2013, Soren Brinkmann wrote:
> > From: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> >
> > On most ARM systems the per-cpu clockevents are truly per-cpu in
> > the sense that they can't be controlled on any other CPU besides
> > the CPU that they interrupt. If one of these clockevents were to
> > become a broadcast source we will run into a lot of trouble
> > because the broadcast source is enabled on the first CPU to go
> > into deep idle (if that CPU suffers from FEAT_C3_STOP) and that
> > could be a different CPU than what the clockevent is interrupting
> > (or even worse the CPU that the clockevent interrupts could be
> > offline).
> >
> > Theoretically it's possible to support per-cpu clockevents as the
> > broadcast source but so far we haven't needed this and supporting
> > it is rather complicated. Let's just deny the possibility for now
> > until this becomes a reality (let's hope it never does!).
>
> Well, we can't do it this way. There are globally accessible clock
> event devices which deliver only to cpu0. So the mask check might be
> causing failure here.
>
> Just add a feature flag CLOCK_EVT_FEAT_PERCPU to the clock event
> device and check for it.
I gave it a shot. Is this what you imagine:
diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
index b66c1f3..c639b1a 100644
--- a/drivers/clocksource/arm_global_timer.c
+++ b/drivers/clocksource/arm_global_timer.c
@@ -169,7 +169,8 @@ static int gt_clockevents_init(struct clock_event_device *clk)
int cpu = smp_processor_id();
clk->name = "arm_global_timer";
- clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
+ clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
+ CLOCK_EVT_FEAT_PERCPU;
clk->set_mode = gt_clockevent_set_mode;
clk->set_next_event = gt_clockevent_set_next_event;
clk->cpumask = cpumask_of(cpu);
diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 0857922..493aa02 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -60,6 +60,7 @@ enum clock_event_mode {
* Core shall set the interrupt affinity dynamically in broadcast mode
*/
#define CLOCK_EVT_FEAT_DYNIRQ 0x000020
+#define CLOCK_EVT_FEAT_PERCPU 0x000040
/**
* struct clock_event_device - clock event device descriptor
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index d3539e5..de4c5d8 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -70,16 +70,14 @@ static bool tick_check_broadcast_device(struct clock_event_device *curdev,
struct clock_event_device *newdev)
{
if ((newdev->features & CLOCK_EVT_FEAT_DUMMY) ||
- (newdev->features & CLOCK_EVT_FEAT_C3STOP))
+ (newdev->features & CLOCK_EVT_FEAT_C3STOP) ||
+ (newdev->features & CLOCK_EVT_FEAT_PERCPU))
return false;
if (tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT &&
!(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;
}
If this is the way to go, I can prepare this in a v2.
Thanks,
Sören
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