On Tue, Oct 23, 2012 at 06:35:43PM +0100, Lorenzo Pieralisi wrote:

On Tue, Oct 23, 2012 at 04:22:59PM +0100, Shawn Guo wrote:

[...]

quoted

+/*
+ * For each cpu, setup the broadcast timer because local timer
+ * stops for the states other than WFI.
+ */
+static void imx6q_setup_broadcast_timer(void *arg)
+{
+       int cpu = smp_processor_id();
+
+       clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ON, &cpu);
+}

Can anyone explain to me please why this is needed ?

It basically does nothing if either NO_HZ or HIGH_RES_TIMERS is
enabled, in which case tick_broadcast_setup_oneshot is already called
on init_timers path to set up bc->event_handler.  This is the general
case since nowadays we have both options enabled by default for most
systems.

However if neither option is enabled, CLOCK_EVT_NOTIFY_BROADCAST_ON
notifying will help route to call tick_broadcast_setup_oneshot to have
bc->event_handler set up.

So in short, it's needed to have broadcast timer work as expected when
neither NO_HZ or HIGH_RES_TIMERS is enabled.

Shawn