ARM: bcm2836: Send event when onlining other cores

Secondary cores should enter a low-power idle state when waiting to
be started. The "wfe" instruction causes a core to wait until an event
or interrupt arrives before continuing to the next instruction, and
the "sev" instruction sends a wakeup event to the other cores.

Add an "sev" (and a memory barrier) to bcm2836_boot_secondary, the
function that wakes the waiting cores during booting. This is required
if the secondary cores are sitting in "wfe", and harmless if not.
Signed-off-by: NPhil Elwell <phil@raspberrypi.org>
Signed-off-by: NEric Anholt <eric@anholt.net>
Reviewed-by: NEric Anholt <eric@anholt.net>

arch/arm/mach-bcm/platsmp.c

@@ -312,6 +312,9 @@ static int bcm2836_boot_secondary(unsigned int cpu, struct task_struct *idle)
 	writel(virt_to_phys(secondary_startup),
 	       intc_base + LOCAL_MAILBOX3_SET0 + 16 * cpu);
 
+	dsb(sy);
+	sev();
+
 	iounmap(intc_base);
 
 	return 0;