xen/events: use the FIFO-based ABI if available

Implement all the event channel port ops for the FIFO-based ABI.

If the hypervisor supports the FIFO-based ABI, enable it by
initializing the control block for the boot VCPU and subsequent VCPUs
as they are brought up and on resume.  The event array is expanded as
required when event ports are setup.

The 'xen.fifo_events=0' command line option may be used to disable use
of the FIFO-based ABI.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/events/Makefile

@@ -2,3 +2,4 @@ obj-y += events.o
 
 events-y += events_base.o
 events-y += events_2l.o
+events-y += events_fifo.o

drivers/xen/events/events_base.c

@@ -1563,6 +1563,7 @@ void xen_irq_resume(void)
 
 	/* New event-channel space is not 'live' yet. */
 	xen_evtchn_mask_all();
+	xen_evtchn_resume();
 
 	/* No IRQ <-> event-channel mappings. */
 	list_for_each_entry(info, &xen_irq_list_head, list)
@@ -1659,9 +1660,20 @@ void xen_callback_vector(void)
 void xen_callback_vector(void) {}
 #endif
 
+#undef MODULE_PARAM_PREFIX
+#define MODULE_PARAM_PREFIX "xen."
+
+static bool fifo_events = true;
+module_param(fifo_events, bool, 0);
+
 void __init xen_init_IRQ(void)
 {
-	xen_evtchn_2l_init();
+	int ret = -EINVAL;
+
+	if (fifo_events)
+		ret = xen_evtchn_fifo_init();
+	if (ret < 0)
+		xen_evtchn_2l_init();
 
 	evtchn_to_irq = kcalloc(EVTCHN_ROW(xen_evtchn_max_channels()),
 				sizeof(*evtchn_to_irq), GFP_KERNEL);