usb: cdc-acm: send zero packet for intel 7260 modem

commit ffdb1e36 upstream.

For Intel 7260 modem, it is needed for host side to send zero
packet if the BULK OUT size is equal to USB endpoint max packet
length. Otherwise, modem side may still wait for more data and
cannot give response to host side.
Signed-off-by: Konrad Leszczynski <konrad.leszczynski@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ kamal: backport to 3.13-stable: hardcode BIT(8) ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/usb/class/cdc-acm.c

@@ -1272,6 +1272,8 @@ static int acm_probe(struct usb_interface *intf,
 				usb_sndbulkpipe(usb_dev, epwrite->bEndpointAddress),
 				NULL, acm->writesize, acm_write_bulk, snd);
 		snd->urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+		if (quirks & SEND_ZERO_PACKET)
+			snd->urb->transfer_flags |= URB_ZERO_PACKET;
 		snd->instance = acm;
 	}
 
@@ -1743,6 +1745,10 @@ static const struct usb_device_id acm_ids[] = {
 	{ USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
 		USB_CDC_ACM_PROTO_AT_CDMA) },
 
+	{ USB_DEVICE(0x1519, 0x0452), /* Intel 7260 modem */
+	.driver_info = SEND_ZERO_PACKET,
+	},
+
 	{ }
 };
 

drivers/usb/class/cdc-acm.h

@@ -130,3 +130,4 @@ struct acm {
 #define NO_DATA_INTERFACE		16
 #define IGNORE_DEVICE			32
 #define CLEAR_HALT_CONDITIONS		128
+#define SEND_ZERO_PACKET		256