usb: gadget: u_ether: prepare for NCM

NCM is a Network Control Model, subclass of USB CDC class,
specification is available at http://www.usb.org/developers/devclass_docs

This patch makes possible for u_ether to use multiply of wMaxPacketSize
predefined size transfers without ZLP (Zero Length Packet), required
by NCM spec.
Signed-off-by: NYauheni Kaliuta <yauheni.kaliuta@nokia.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/u_ether.c

@@ -240,6 +240,9 @@ rx_submit(struct eth_dev *dev, struct usb_request *req, gfp_t gfp_flags)
 	size += out->maxpacket - 1;
 	size -= size % out->maxpacket;
 
+	if (dev->port_usb->is_fixed)
+		size = max(size, dev->port_usb->fixed_out_len);
+
 	skb = alloc_skb(size + NET_IP_ALIGN, gfp_flags);
 	if (skb == NULL) {
 		DBG(dev, "no rx skb\n");
@@ -578,12 +581,19 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
 	req->context = skb;
 	req->complete = tx_complete;
 
+	/* NCM requires no zlp if transfer is dwNtbInMaxSize */
+	if (dev->port_usb->is_fixed &&
+	    length == dev->port_usb->fixed_in_len &&
+	    (length % in->maxpacket) == 0)
+		req->zero = 0;
+	else
+		req->zero = 1;
+
 	/* use zlp framing on tx for strict CDC-Ether conformance,
 	 * though any robust network rx path ignores extra padding.
 	 * and some hardware doesn't like to write zlps.
 	 */
-	req->zero = 1;
-	if (!dev->zlp && (length % in->maxpacket) == 0)
+	if (req->zero && !dev->zlp && (length % in->maxpacket) == 0)
 		length++;
 
 	req->length = length;

drivers/usb/gadget/u_ether.h

@@ -62,6 +62,10 @@ struct gether {
 
 	/* hooks for added framing, as needed for RNDIS and EEM. */
 	u32				header_len;
+	/* NCM requires fixed size bundles */
+	bool				is_fixed;
+	u32				fixed_out_len;
+	u32				fixed_in_len;
 	struct sk_buff			*(*wrap)(struct gether *port,
 						struct sk_buff *skb);
 	int				(*unwrap)(struct gether *port,