1 files changed, 28 insertions, 3 deletions

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index f0bf01ea069a..ebaf7500f48f 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -37,6 +37,8 @@ struct xencons_info {
 	struct xenbus_device *xbdev;
 	struct xencons_interface *intf;
 	unsigned int evtchn;
+	XENCONS_RING_IDX out_cons;
+	unsigned int out_cons_same;
 	struct hvc_struct *hvc;
 	int irq;
 	int vtermno;
@@ -138,6 +140,8 @@ static int domU_read_console(uint32_t vtermno, char *buf, int len)
 	XENCONS_RING_IDX cons, prod;
 	int recv = 0;
 	struct xencons_info *xencons = vtermno_to_xencons(vtermno);
+	unsigned int eoiflag = 0;
+
 	if (xencons == NULL)
 		return -EINVAL;
 	intf = xencons->intf;
@@ -157,7 +161,27 @@ static int domU_read_console(uint32_t vtermno, char *buf, int len)
 	mb();			/* read ring before consuming */
 	intf->in_cons = cons;
 
-	notify_daemon(xencons);
+	/*
+	 * When to mark interrupt having been spurious:
+	 * - there was no new data to be read, and
+	 * - the backend did not consume some output bytes, and
+	 * - the previous round with no read data didn't see consumed bytes
+	 *   (we might have a race with an interrupt being in flight while
+	 *   updating xencons->out_cons, so account for that by allowing one
+	 *   round without any visible reason)
+	 */
+	if (intf->out_cons != xencons->out_cons) {
+		xencons->out_cons = intf->out_cons;
+		xencons->out_cons_same = 0;
+	}
+	if (recv) {
+		notify_daemon(xencons);
+	} else if (xencons->out_cons_same++ > 1) {
+		eoiflag = XEN_EOI_FLAG_SPURIOUS;
+	}
+
+	xen_irq_lateeoi(xencons->irq, eoiflag);
+
 	return recv;
 }
 
@@ -386,7 +410,7 @@ static int xencons_connect_backend(struct xenbus_device *dev,
 	if (ret)
 		return ret;
 	info->evtchn = evtchn;
-	irq = bind_evtchn_to_irq(evtchn);
+	irq = bind_interdomain_evtchn_to_irq_lateeoi(dev, evtchn);
 	if (irq < 0)
 		return irq;
 	info->irq = irq;
@@ -522,6 +546,7 @@ static struct xenbus_driver xencons_driver = {
 	.remove = xencons_remove,
 	.resume = xencons_resume,
 	.otherend_changed = xencons_backend_changed,
+	.not_essential = true,
 };
 #endif /* CONFIG_HVC_XEN_FRONTEND */
 
@@ -550,7 +575,7 @@ static int __init xen_hvc_init(void)
 			return r;
 
 		info = vtermno_to_xencons(HVC_COOKIE);
-		info->irq = bind_evtchn_to_irq(info->evtchn);
+		info->irq = bind_evtchn_to_irq_lateeoi(info->evtchn);
 	}
 	if (info->irq < 0)
 		info->irq = 0; /* NO_IRQ */