powerpc/opal: Wake up kopald polling thread before waiting for events

On some environments (prototype machines, some simulators, etc...)
there is no functional interrupt source to signal completion, so
we rely on the fairly slow OPAL heartbeat.

In a number of cases, the calls complete very quickly or even
immediately. We've observed that it helps a lot to wakeup the OPAL
heartbeat thread before waiting for event in those cases, it will
call OPAL immediately to collect completions for anything that
finished fast enough.

Signed-off-by: Benjamin Herrenschmidt <[e-mail]>
Acked-By: Michael Neuling <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/include/asm/opal.h

···
 		return be64_to_cpu(msg.params[1]);
 }
 
+void opal_wake_poller(void);
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_POWERPC_OPAL_H */

arch/powerpc/platforms/powernv/opal-async.c

···
 		return -EINVAL;
 	}
 
+	/* Wakeup the poller before we wait for events to speed things
+	 * up on platforms or simulators where the interrupts aren't
+	 * functional.
+	 */
+	opal_wake_poller();
 	wait_event(opal_async_wait, test_bit(token, opal_async_complete_map));
 	memcpy(msg, &opal_async_responses[token], sizeof(*msg));
 

arch/powerpc/platforms/powernv/opal.c

···
 static DEFINE_SPINLOCK(opal_write_lock);
 static struct atomic_notifier_head opal_msg_notifier_head[OPAL_MSG_TYPE_MAX];
 static uint32_t opal_heartbeat;
+static struct task_struct *kopald_tsk;
 
 static void opal_reinit_cores(void)
 {
···
 
 static int kopald(void *unused)
 {
+	unsigned long timeout = msecs_to_jiffies(opal_heartbeat) + 1;
 	__be64 events;
 
 	set_freezable();
···
 		try_to_freeze();
 		opal_poll_events(&events);
 		opal_handle_events(be64_to_cpu(events));
-		msleep_interruptible(opal_heartbeat);
+		schedule_timeout_interruptible(timeout);
 	} while (!kthread_should_stop());
 
 	return 0;
+}
+
+void opal_wake_poller(void)
+{
+	if (kopald_tsk)
+		wake_up_process(kopald_tsk);
 }
 
 static void opal_init_heartbeat(void)
···
 		opal_heartbeat = 0;
 
 	if (opal_heartbeat)
-		kthread_run(kopald, NULL, "kopald");
+		kopald_tsk = kthread_run(kopald, NULL, "kopald");
 }
 
 static int __init opal_init(void)