USBNET: fix handling padding packet

Commit 638c5115a7949(USBNET: support DMA SG) introduces DMA SG
if the usb host controller is capable of building packet from
discontinuous buffers, but missed handling padding packet when
building DMA SG.

This patch attachs the pre-allocated padding packet at the
end of the sg list, so padding packet can be sent to device
if drivers require that.

Reported-by: David Laight <David.Laight@aculab.com>
Acked-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 21 insertions, 6 deletions

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 7b331e613e02..bf94e10a37c8 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1241,7 +1241,9 @@ static int build_dma_sg(const struct sk_buff *skb, struct urb *urb)
         if (num_sgs == 1)
                 return 0;
 
-        urb->sg = kmalloc(num_sgs * sizeof(struct scatterlist), GFP_ATOMIC);
+        /* reserve one for zero packet */
+        urb->sg = kmalloc((num_sgs + 1) * sizeof(struct scatterlist),
+                          GFP_ATOMIC);
         if (!urb->sg)
                 return -ENOMEM;
 
@@ -1305,7 +1307,7 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
                 if (build_dma_sg(skb, urb) < 0)
                         goto drop;
         }
-        entry->length = length = urb->transfer_buffer_length;
+        length = urb->transfer_buffer_length;
 
         /* don't assume the hardware handles USB_ZERO_PACKET
          * NOTE:  strictly conforming cdc-ether devices should expect
@@ -1317,15 +1319,18 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
         if (length % dev->maxpacket == 0) {
                 if (!(info->flags & FLAG_SEND_ZLP)) {
                         if (!(info->flags & FLAG_MULTI_PACKET)) {
-                                urb->transfer_buffer_length++;
-                                if (skb_tailroom(skb)) {
+                                length++;
+                                if (skb_tailroom(skb) && !urb->num_sgs) {
                                         skb->data[skb->len] = 0;
                                         __skb_put(skb, 1);
-                                }
+                                } else if (urb->num_sgs)
+                                        sg_set_buf(&urb->sg[urb->num_sgs++],
+                                                        dev->padding_pkt, 1);
                         }
                 } else
                         urb->transfer_flags |= URB_ZERO_PACKET;
         }
+        entry->length = urb->transfer_buffer_length = length;
 
         spin_lock_irqsave(&dev->txq.lock, flags);
         retval = usb_autopm_get_interface_async(dev->intf);
@@ -1509,6 +1514,7 @@ void usbnet_disconnect (struct usb_interface *intf)
 
         usb_kill_urb(dev->interrupt);
         usb_free_urb(dev->interrupt);
+        kfree(dev->padding_pkt);
 
         free_netdev(net);
 }
@@ -1679,9 +1685,16 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
         /* initialize max rx_qlen and tx_qlen */
         usbnet_update_max_qlen(dev);
 
+        if (dev->can_dma_sg && !(info->flags & FLAG_SEND_ZLP) &&
+                !(info->flags & FLAG_MULTI_PACKET)) {
+                dev->padding_pkt = kzalloc(1, GFP_KERNEL);
+                if (!dev->padding_pkt)
+                        goto out4;
+        }
+
         status = register_netdev (net);
         if (status)
-                goto out4;
+                goto out5;
         netif_info(dev, probe, dev->net,
                    "register '%s' at usb-%s-%s, %s, %pM\n",
                    udev->dev.driver->name,
@@ -1699,6 +1712,8 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 
         return 0;
 
+out5:
+        kfree(dev->padding_pkt);
 out4:
         usb_free_urb(dev->interrupt);
 out3: