usb: gadget: ether: fix clog tx transmit

With g_len initial from 0 and buffer size is 10, it cause interrupt(IOC)
is triggered at entry 0 and 5, which is 1st and 6th entry in list. This deviate
double bufferring design that expect to trigger interrupt at half and full.
If interrupt is trggered at 0 and 5, when upper layer pass through data faster
then u_ether driver can free up, then the data flow start clogging from g_len=6
till g_len=9 and no interrupt is triggered to free up memory to consume data
from upper layer as illustrated below.

[0][1][2][3][4] [5][6][7][8][9]
IOC             IOC

Initial g_len as 1, so interrupt will be triggered at 5th and 10th as illustrated
below. Especially, 10th entry, which is also last entry, must set interrupt to
free up memory.

[0][1][2][3][4] [5][6][7][8][9]
            IOC             IOC

Also enforce last entry in list to trigger interrupt in case user space
change qmult value at run time that will cause misalignment with buffer size.

For example:
echo 4 > /sys/module/g_android/parameters/qmult

[0][1][2][3][4] [5][6][7][8][9]
         IOC          IOC   IOC

bug 1054552
Reviewed-on: http://git-master/r/139969
(cherry picked from commit 4ea9a0eff24d5f3c44402732e35bf12eaed7ed79)

Change-Id: I449a007036f6aea73626921bb24925b2ec57e167
Signed-off-by: Jay Cheng <jacheng@nvidia.com>
Reviewed-on: http://git-master/r/145243
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Venkat Moganty <vmoganty@nvidia.com>
Reviewed-by: Michael Hsu <mhsu@nvidia.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/drivers/usb/gadget/u_ether.c b/drivers/usb/gadget/u_ether.c
index dd2615a3f65e..4056b9be378d 100644
--- a/drivers/usb/gadget/u_ether.c
+++ b/drivers/usb/gadget/u_ether.c
@@ -496,6 +496,7 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
 	unsigned long		flags;
 	struct usb_ep		*in;
 	u16			cdc_filter;
+	int			buffer_is_full = 0;
 
 	spin_lock_irqsave(&dev->lock, flags);
 	if (dev->port_usb) {
@@ -549,8 +550,10 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
 	list_del(&req->list);
 
 	/* temporarily stop TX queue when the freelist empties */
-	if (list_empty(&dev->tx_reqs))
+	if (list_empty(&dev->tx_reqs)) {
+		buffer_is_full = 1;
 		netif_stop_queue(net);
+	}
 	spin_unlock_irqrestore(&dev->req_lock, flags);
 
 	/* no buffer copies needed, unless the network stack did it
@@ -590,13 +593,19 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
 
 	req->length = length;
 
+	/* In case user change qmult after f_rndis is enabled, qmult might be
+	 * misaligned with buffer size. Always enable interrupt when buffer
+	 * is full
+	 */
+	if (buffer_is_full)
+		req->no_interrupt = 0;
+
 	/* throttle high/super speed IRQ rate back slightly */
-	if (gadget_is_dualspeed(dev->gadget))
+	else if (gadget_is_dualspeed(dev->gadget))
 		req->no_interrupt = (dev->gadget->speed == USB_SPEED_HIGH ||
 				     dev->gadget->speed == USB_SPEED_SUPER)
 			? ((atomic_read(&dev->tx_qlen) % qmult) != 0)
 			: 0;
-
 	retval = usb_ep_queue(in, req, GFP_ATOMIC);
 	switch (retval) {
 	default:
@@ -630,7 +639,7 @@ static void eth_start(struct eth_dev *dev, gfp_t gfp_flags)
 	rx_fill(dev, gfp_flags);
 
 	/* and open the tx floodgates */
-	atomic_set(&dev->tx_qlen, 0);
+	atomic_set(&dev->tx_qlen, 1);
 	netif_wake_queue(dev->net);
 }