tick: broadcast: Deny per-cpu clockevents from being broadcast sources

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!).

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Michal Simek <michal.simek@xilinx.com>

kernel/time/tick-broadcast.c

@@ -70,6 +70,7 @@ 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_PERCPU) ||
 	    (newdev->features & CLOCK_EVT_FEAT_C3STOP))
 		return false;