[RFC][PATCH] usb: gadget: u_ether: Add workqueue as bottom half handler for rx data path

[Amit Pundir]

From: Badhri Jagan Sridharan <Badhri@xxxxxxxxxx>

u_ether driver passes rx data to network layer and resubmits the
request back to usb hardware in interrupt context. Network layer
processes rx data by scheduling tasklet. For high throughput
scenarios on rx data path driver is spending lot of time in interrupt
context due to rx data processing by tasklet and continuous completion
and re-submission of the usb requests which results in watchdog bark.
Hence move the rx data processing and usb request submission to a
workqueue bottom half handler.

Cc: Felipe Balbi <balbi@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Mike Looijmans <mike.looijmans@xxxxxxxx> 
Cc: Robert Baldyga <r.baldyga@xxxxxxxxxxx>
Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Signed-off-by: Badhri Jagan Sridharan <Badhri@xxxxxxxxxx>
[pundir: cherry-picked this patch from AOSP experimental/android-4.4 tree.]
Signed-off-by: Amit Pundir <amit.pundir@xxxxxxxxxx>
---
Cherry-picked this patch from AOSP common/experimental/android-4.4 tree.
I could not find upstream submission history for this patch, so my
apologies in advance if this has already been NACKed before.

 drivers/usb/gadget/function/u_ether.c | 119 +++++++++++++++++++++++-----------
 1 file changed, 80 insertions(+), 39 deletions(-)

diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
index 7f98a2d..4235c33 100644
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -53,6 +53,8 @@
  * blocks and still have efficient handling. */
 #define GETHER_MAX_ETH_FRAME_LEN 15412
 
+static struct workqueue_struct	*uether_wq;
+
 struct eth_dev {
 	/* lock is held while accessing port_usb
 	 */
@@ -77,6 +79,7 @@ struct eth_dev {
 						struct sk_buff_head *list);
 
 	struct work_struct	work;
+	struct work_struct	rx_work;
 
 	unsigned long		todo;
 #define	WORK_RX_MEMORY		0
@@ -248,18 +251,16 @@ enomem:
 		DBG(dev, "rx submit --> %d\n", retval);
 		if (skb)
 			dev_kfree_skb_any(skb);
-		spin_lock_irqsave(&dev->req_lock, flags);
-		list_add(&req->list, &dev->rx_reqs);
-		spin_unlock_irqrestore(&dev->req_lock, flags);
 	}
 	return retval;
 }
 
 static void rx_complete(struct usb_ep *ep, struct usb_request *req)
 {
-	struct sk_buff	*skb = req->context, *skb2;
+	struct sk_buff	*skb = req->context;
 	struct eth_dev	*dev = ep->driver_data;
 	int		status = req->status;
+	bool		queue = 0;
 
 	switch (status) {
 
@@ -283,30 +284,8 @@ static void rx_complete(struct usb_ep *ep, struct usb_request *req)
 		} else {
 			skb_queue_tail(&dev->rx_frames, skb);
 		}
-		skb = NULL;
-
-		skb2 = skb_dequeue(&dev->rx_frames);
-		while (skb2) {
-			if (status < 0
-					|| ETH_HLEN > skb2->len
-					|| skb2->len > GETHER_MAX_ETH_FRAME_LEN) {
-				dev->net->stats.rx_errors++;
-				dev->net->stats.rx_length_errors++;
-				DBG(dev, "rx length %d\n", skb2->len);
-				dev_kfree_skb_any(skb2);
-				goto next_frame;
-			}
-			skb2->protocol = eth_type_trans(skb2, dev->net);
-			dev->net->stats.rx_packets++;
-			dev->net->stats.rx_bytes += skb2->len;
-
-			/* no buffer copies needed, unless hardware can't
-			 * use skb buffers.
-			 */
-			status = netif_rx(skb2);
-next_frame:
-			skb2 = skb_dequeue(&dev->rx_frames);
-		}
+		if (!status)
+			queue = 1;
 		break;
 
 	/* software-driven interface shutdown */
@@ -329,22 +308,20 @@ quiesce:
 		/* FALLTHROUGH */
 
 	default:
+		queue = 1;
+		dev_kfree_skb_any(skb);
 		dev->net->stats.rx_errors++;
 		DBG(dev, "rx status %d\n", status);
 		break;
 	}
 
-	if (skb)
-		dev_kfree_skb_any(skb);
-	if (!netif_running(dev->net)) {
 clean:
-		spin_lock(&dev->req_lock);
-		list_add(&req->list, &dev->rx_reqs);
-		spin_unlock(&dev->req_lock);
-		req = NULL;
-	}
-	if (req)
-		rx_submit(dev, req, GFP_ATOMIC);
+	spin_lock(&dev->req_lock);
+	list_add(&req->list, &dev->rx_reqs);
+	spin_unlock(&dev->req_lock);
+
+	if (queue)
+		queue_work(uether_wq, &dev->rx_work);
 }
 
 static int prealloc(struct list_head *list, struct usb_ep *ep, unsigned n)
@@ -409,16 +386,24 @@ static void rx_fill(struct eth_dev *dev, gfp_t gfp_flags)
 {
 	struct usb_request	*req;
 	unsigned long		flags;
+	int			req_cnt = 0;
 
 	/* fill unused rxq slots with some skb */
 	spin_lock_irqsave(&dev->req_lock, flags);
 	while (!list_empty(&dev->rx_reqs)) {
+		/* break the nexus of continuous completion and re-submission*/
+		if (++req_cnt > qlen(dev->gadget))
+			break;
+
 		req = container_of(dev->rx_reqs.next,
 				struct usb_request, list);
 		list_del_init(&req->list);
 		spin_unlock_irqrestore(&dev->req_lock, flags);
 
 		if (rx_submit(dev, req, gfp_flags) < 0) {
+			spin_lock_irqsave(&dev->req_lock, flags);
+			list_add(&req->list, &dev->rx_reqs);
+			spin_unlock_irqrestore(&dev->req_lock, flags);
 			defer_kevent(dev, WORK_RX_MEMORY);
 			return;
 		}
@@ -428,6 +413,36 @@ static void rx_fill(struct eth_dev *dev, gfp_t gfp_flags)
 	spin_unlock_irqrestore(&dev->req_lock, flags);
 }
 
+static void process_rx_w(struct work_struct *work)
+{
+	struct eth_dev	*dev = container_of(work, struct eth_dev, rx_work);
+	struct sk_buff	*skb;
+	int		status = 0;
+
+	if (!dev->port_usb)
+		return;
+
+	while ((skb = skb_dequeue(&dev->rx_frames))) {
+		if (status < 0
+				|| ETH_HLEN > skb->len
+				|| skb->len > ETH_FRAME_LEN) {
+			dev->net->stats.rx_errors++;
+			dev->net->stats.rx_length_errors++;
+			DBG(dev, "rx length %d\n", skb->len);
+			dev_kfree_skb_any(skb);
+			continue;
+		}
+		skb->protocol = eth_type_trans(skb, dev->net);
+		dev->net->stats.rx_packets++;
+		dev->net->stats.rx_bytes += skb->len;
+
+		status = netif_rx_ni(skb);
+	}
+
+	if (netif_running(dev->net))
+		rx_fill(dev, GFP_KERNEL);
+}
+
 static void eth_work(struct work_struct *work)
 {
 	struct eth_dev	*dev = container_of(work, struct eth_dev, work);
@@ -789,6 +804,7 @@ struct eth_dev *gether_setup_name(struct usb_gadget *g,
 	spin_lock_init(&dev->lock);
 	spin_lock_init(&dev->req_lock);
 	INIT_WORK(&dev->work, eth_work);
+	INIT_WORK(&dev->rx_work, process_rx_w);
 	INIT_LIST_HEAD(&dev->tx_reqs);
 	INIT_LIST_HEAD(&dev->rx_reqs);
 
@@ -1134,6 +1150,7 @@ void gether_disconnect(struct gether *link)
 {
 	struct eth_dev		*dev = link->ioport;
 	struct usb_request	*req;
+	struct sk_buff		*skb;
 
 	WARN_ON(!dev);
 	if (!dev)
@@ -1174,6 +1191,12 @@ void gether_disconnect(struct gether *link)
 		spin_lock(&dev->req_lock);
 	}
 	spin_unlock(&dev->req_lock);
+
+	spin_lock(&dev->rx_frames.lock);
+	while ((skb = __skb_dequeue(&dev->rx_frames)))
+		dev_kfree_skb_any(skb);
+	spin_unlock(&dev->rx_frames.lock);
+
 	link->out_ep->desc = NULL;
 
 	/* finish forgetting about this USB link episode */
@@ -1187,5 +1210,23 @@ void gether_disconnect(struct gether *link)
 }
 EXPORT_SYMBOL_GPL(gether_disconnect);
 
-MODULE_LICENSE("GPL");
+static int __init gether_init(void)
+{
+	uether_wq  = create_singlethread_workqueue("uether");
+	if (!uether_wq) {
+		pr_err("%s: Unable to create workqueue: uether\n", __func__);
+		return -ENOMEM;
+	}
+	return 0;
+}
+module_init(gether_init);
+
+static void __exit gether_exit(void)
+{
+	destroy_workqueue(uether_wq);
+
+}
+module_exit(gether_exit);
 MODULE_AUTHOR("David Brownell");
+MODULE_DESCRIPTION("ethernet over USB driver");
+MODULE_LICENSE("GPL v2");
-- 
1.9.1