xen/events: allow event channel priority to be set

Add xen_irq_set_priority() to set an event channels priority.  This function
will only work with event channel ABIs that support priority (i.e., 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/events_base.c

@@ -1117,6 +1117,23 @@ void unbind_from_irqhandler(unsigned int irq, void *dev_id)
 }
 EXPORT_SYMBOL_GPL(unbind_from_irqhandler);
 
+/**
+ * xen_set_irq_priority() - set an event channel priority.
+ * @irq:irq bound to an event channel.
+ * @priority: priority between XEN_IRQ_PRIORITY_MAX and XEN_IRQ_PRIORITY_MIN.
+ */
+int xen_set_irq_priority(unsigned irq, unsigned priority)
+{
+	struct evtchn_set_priority set_priority;
+
+	set_priority.port = evtchn_from_irq(irq);
+	set_priority.priority = priority;
+
+	return HYPERVISOR_event_channel_op(EVTCHNOP_set_priority,
+					   &set_priority);
+}
+EXPORT_SYMBOL_GPL(xen_set_irq_priority);
+
 int evtchn_make_refcounted(unsigned int evtchn)
 {
 	int irq = get_evtchn_to_irq(evtchn);

include/xen/events.h

@@ -39,6 +39,11 @@ int bind_interdomain_evtchn_to_irqhandler(unsigned int remote_domain,
  */
 void unbind_from_irqhandler(unsigned int irq, void *dev_id);
 
+#define XEN_IRQ_PRIORITY_MAX     EVTCHN_FIFO_PRIORITY_MAX
+#define XEN_IRQ_PRIORITY_DEFAULT EVTCHN_FIFO_PRIORITY_DEFAULT
+#define XEN_IRQ_PRIORITY_MIN     EVTCHN_FIFO_PRIORITY_MIN
+int xen_set_irq_priority(unsigned irq, unsigned priority);
+
 /*
  * Allow extra references to event channels exposed to userspace by evtchn
  */