xen-netfront: split event channels support for Xen frontend driver

This patch adds a new feature called feature-split-event-channels for
netfront, enabling it to handle TX and RX events separately.

If netback does not support this feature, it falls back to use single event
channel.

If netfront fails to setup split event channels, it will try falling back to
single event channel.
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netfront.c

@@ -85,7 +85,15 @@ struct netfront_info {
 
 	struct napi_struct napi;
 
-	unsigned int evtchn;
+	/* Split event channels support, tx_* == rx_* when using
+	 * single event channel.
+	 */
+	unsigned int tx_evtchn, rx_evtchn;
+	unsigned int tx_irq, rx_irq;
+	/* Only used when split event channels support is enabled */
+	char tx_irq_name[IFNAMSIZ+4]; /* DEVNAME-tx */
+	char rx_irq_name[IFNAMSIZ+4]; /* DEVNAME-rx */
+
 	struct xenbus_device *xbdev;
 
 	spinlock_t   tx_lock;
@@ -330,7 +338,7 @@ static void xennet_alloc_rx_buffers(struct net_device *dev)
  push:
 	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&np->rx, notify);
 	if (notify)
-		notify_remote_via_irq(np->netdev->irq);
+		notify_remote_via_irq(np->rx_irq);
 }
 
 static int xennet_open(struct net_device *dev)
@@ -623,7 +631,7 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&np->tx, notify);
 	if (notify)
-		notify_remote_via_irq(np->netdev->irq);
+		notify_remote_via_irq(np->tx_irq);
 
 	u64_stats_update_begin(&stats->syncp);
 	stats->tx_bytes += skb->len;
@@ -1254,23 +1262,35 @@ static int xennet_set_features(struct net_device *dev,
 	return 0;
 }
 
-static irqreturn_t xennet_interrupt(int irq, void *dev_id)
+static irqreturn_t xennet_tx_interrupt(int irq, void *dev_id)
 {
-	struct net_device *dev = dev_id;
-	struct netfront_info *np = netdev_priv(dev);
+	struct netfront_info *np = dev_id;
+	struct net_device *dev = np->netdev;
 	unsigned long flags;
 
 	spin_lock_irqsave(&np->tx_lock, flags);
+	xennet_tx_buf_gc(dev);
+	spin_unlock_irqrestore(&np->tx_lock, flags);
 
-	if (likely(netif_carrier_ok(dev))) {
-		xennet_tx_buf_gc(dev);
-		/* Under tx_lock: protects access to rx shared-ring indexes. */
-		if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t xennet_rx_interrupt(int irq, void *dev_id)
+{
+	struct netfront_info *np = dev_id;
+	struct net_device *dev = np->netdev;
+
+	if (likely(netif_carrier_ok(dev) &&
+		   RING_HAS_UNCONSUMED_RESPONSES(&np->rx)))
 			napi_schedule(&np->napi);
-	}
 
-	spin_unlock_irqrestore(&np->tx_lock, flags);
+	return IRQ_HANDLED;
+}
 
+static irqreturn_t xennet_interrupt(int irq, void *dev_id)
+{
+	xennet_tx_interrupt(irq, dev_id);
+	xennet_rx_interrupt(irq, dev_id);
 	return IRQ_HANDLED;
 }
 
@@ -1451,9 +1471,14 @@ static void xennet_disconnect_backend(struct netfront_info *info)
 	spin_unlock_irq(&info->tx_lock);
 	spin_unlock_bh(&info->rx_lock);
 
-	if (info->netdev->irq)
-		unbind_from_irqhandler(info->netdev->irq, info->netdev);
-	info->evtchn = info->netdev->irq = 0;
+	if (info->tx_irq && (info->tx_irq == info->rx_irq))
+		unbind_from_irqhandler(info->tx_irq, info);
+	if (info->tx_irq && (info->tx_irq != info->rx_irq)) {
+		unbind_from_irqhandler(info->tx_irq, info);
+		unbind_from_irqhandler(info->rx_irq, info);
+	}
+	info->tx_evtchn = info->rx_evtchn = 0;
+	info->tx_irq = info->rx_irq = 0;
 
 	/* End access and free the pages */
 	xennet_end_access(info->tx_ring_ref, info->tx.sring);
@@ -1503,12 +1528,82 @@ static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
 	return 0;
 }
 
+static int setup_netfront_single(struct netfront_info *info)
+{
+	int err;
+
+	err = xenbus_alloc_evtchn(info->xbdev, &info->tx_evtchn);
+	if (err < 0)
+		goto fail;
+
+	err = bind_evtchn_to_irqhandler(info->tx_evtchn,
+					xennet_interrupt,
+					0, info->netdev->name, info);
+	if (err < 0)
+		goto bind_fail;
+	info->rx_evtchn = info->tx_evtchn;
+	info->rx_irq = info->tx_irq = err;
+
+	return 0;
+
+bind_fail:
+	xenbus_free_evtchn(info->xbdev, info->tx_evtchn);
+	info->tx_evtchn = 0;
+fail:
+	return err;
+}
+
+static int setup_netfront_split(struct netfront_info *info)
+{
+	int err;
+
+	err = xenbus_alloc_evtchn(info->xbdev, &info->tx_evtchn);
+	if (err < 0)
+		goto fail;
+	err = xenbus_alloc_evtchn(info->xbdev, &info->rx_evtchn);
+	if (err < 0)
+		goto alloc_rx_evtchn_fail;
+
+	snprintf(info->tx_irq_name, sizeof(info->tx_irq_name),
+		 "%s-tx", info->netdev->name);
+	err = bind_evtchn_to_irqhandler(info->tx_evtchn,
+					xennet_tx_interrupt,
+					0, info->tx_irq_name, info);
+	if (err < 0)
+		goto bind_tx_fail;
+	info->tx_irq = err;
+
+	snprintf(info->rx_irq_name, sizeof(info->rx_irq_name),
+		 "%s-rx", info->netdev->name);
+	err = bind_evtchn_to_irqhandler(info->rx_evtchn,
+					xennet_rx_interrupt,
+					0, info->rx_irq_name, info);
+	if (err < 0)
+		goto bind_rx_fail;
+	info->rx_irq = err;
+
+	return 0;
+
+bind_rx_fail:
+	unbind_from_irqhandler(info->tx_irq, info);
+	info->tx_irq = 0;
+bind_tx_fail:
+	xenbus_free_evtchn(info->xbdev, info->rx_evtchn);
+	info->rx_evtchn = 0;
+alloc_rx_evtchn_fail:
+	xenbus_free_evtchn(info->xbdev, info->tx_evtchn);
+	info->tx_evtchn = 0;
+fail:
+	return err;
+}
+
 static int setup_netfront(struct xenbus_device *dev, struct netfront_info *info)
 {
 	struct xen_netif_tx_sring *txs;
 	struct xen_netif_rx_sring *rxs;
 	int err;
 	struct net_device *netdev = info->netdev;
+	unsigned int feature_split_evtchn;
 
 	info->tx_ring_ref = GRANT_INVALID_REF;
 	info->rx_ring_ref = GRANT_INVALID_REF;
@@ -1516,6 +1611,12 @@ static int setup_netfront(struct xenbus_device *dev, struct netfront_info *info)
 	info->tx.sring = NULL;
 	netdev->irq = 0;
 
+	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+			   "feature-split-event-channels", "%u",
+			   &feature_split_evtchn);
+	if (err < 0)
+		feature_split_evtchn = 0;
+
 	err = xen_net_read_mac(dev, netdev->dev_addr);
 	if (err) {
 		xenbus_dev_fatal(dev, err, "parsing %s/mac", dev->nodename);
@@ -1550,22 +1651,23 @@ static int setup_netfront(struct xenbus_device *dev, struct netfront_info *info)
 		goto grant_rx_ring_fail;
 	info->rx_ring_ref = err;
 
-	err = xenbus_alloc_evtchn(dev, &info->evtchn);
+	if (feature_split_evtchn)
+		err = setup_netfront_split(info);
+	/* setup single event channel if
+	 *  a) feature-split-event-channels == 0
+	 *  b) feature-split-event-channels == 1 but failed to setup
+	 */
+	if (!feature_split_evtchn || (feature_split_evtchn && err))
+		err = setup_netfront_single(info);
+
 	if (err)
 		goto alloc_evtchn_fail;
 
-	err = bind_evtchn_to_irqhandler(info->evtchn, xennet_interrupt,
-					0, netdev->name, netdev);
-	if (err < 0)
-		goto bind_fail;
-	netdev->irq = err;
 	return 0;
 
 	/* If we fail to setup netfront, it is safe to just revoke access to
 	 * granted pages because backend is not accessing it at this point.
 	 */
-bind_fail:
-	xenbus_free_evtchn(dev, info->evtchn);
 alloc_evtchn_fail:
 	gnttab_end_foreign_access_ref(info->rx_ring_ref, 0);
 grant_rx_ring_fail:
@@ -1610,11 +1712,27 @@ static int talk_to_netback(struct xenbus_device *dev,
 		message = "writing rx ring-ref";
 		goto abort_transaction;
 	}
-	err = xenbus_printf(xbt, dev->nodename,
-			    "event-channel", "%u", info->evtchn);
-	if (err) {
-		message = "writing event-channel";
-		goto abort_transaction;
+
+	if (info->tx_evtchn == info->rx_evtchn) {
+		err = xenbus_printf(xbt, dev->nodename,
+				    "event-channel", "%u", info->tx_evtchn);
+		if (err) {
+			message = "writing event-channel";
+			goto abort_transaction;
+		}
+	} else {
+		err = xenbus_printf(xbt, dev->nodename,
+				    "event-channel-tx", "%u", info->tx_evtchn);
+		if (err) {
+			message = "writing event-channel-tx";
+			goto abort_transaction;
+		}
+		err = xenbus_printf(xbt, dev->nodename,
+				    "event-channel-rx", "%u", info->rx_evtchn);
+		if (err) {
+			message = "writing event-channel-rx";
+			goto abort_transaction;
+		}
 	}
 
 	err = xenbus_printf(xbt, dev->nodename, "request-rx-copy", "%u",
@@ -1727,7 +1845,9 @@ static int xennet_connect(struct net_device *dev)
 	 * packets.
 	 */
 	netif_carrier_on(np->netdev);
-	notify_remote_via_irq(np->netdev->irq);
+	notify_remote_via_irq(np->tx_irq);
+	if (np->tx_irq != np->rx_irq)
+		notify_remote_via_irq(np->rx_irq);
 	xennet_tx_buf_gc(dev);
 	xennet_alloc_rx_buffers(dev);