[usb] Generalise zero-length packet generation logic

The decision on whether or not a zero-length packet needs to be
transmitted is independent of the host controller and belongs in the
USB core.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/bus/usb.c

 		 int terminate ) {
 	struct usb_device *usb = ep->usb;
 	struct usb_port *port = usb->port;
+	int zlp;
 	int rc;
 
 	/* Fail immediately if device has been unplugged */
 	     ( ( rc = usb_endpoint_reset ( ep ) ) != 0 ) )
 		return rc;
 
+	/* Append a zero-length packet if necessary */
+	zlp = terminate;
+	if ( iob_len ( iobuf ) & ( ep->mtu - 1 ) )
+		zlp = 0;
+
 	/* Enqueue stream transfer */
-	if ( ( rc = ep->host->stream ( ep, iobuf, terminate ) ) != 0 ) {
+	if ( ( rc = ep->host->stream ( ep, iobuf, zlp ) ) != 0 ) {
 		DBGC ( usb, "USB %s %s could not enqueue stream transfer: %s\n",
 		       usb->name, usb_endpoint_name ( ep ), strerror ( rc ) );
 		return rc;

src/drivers/usb/ehci.c

  *
  * @v ep		USB endpoint
  * @v iobuf		I/O buffer
- * @v terminate		Terminate using a short packet
+ * @v zlp		Append a zero-length packet
  * @ret rc		Return status code
  */
 static int ehci_endpoint_stream ( struct usb_endpoint *ep,
-				  struct io_buffer *iobuf, int terminate ) {
+				  struct io_buffer *iobuf, int zlp ) {
 	struct ehci_endpoint *endpoint = usb_endpoint_get_hostdata ( ep );
 	struct ehci_device *ehci = endpoint->ehci;
 	unsigned int input = ( ep->address & USB_DIR_IN );
 	xfer->flags = ( EHCI_FL_IOC |
 			( input ? EHCI_FL_PID_IN : EHCI_FL_PID_OUT ) );
 	xfer++;
-	if ( terminate && ( ( len & ( ep->mtu - 1 ) ) == 0 ) ) {
+	if ( zlp ) {
 		xfer->data = NULL;
 		xfer->len = 0;
 		assert ( ! input );

src/drivers/usb/uhci.c

  *
  * @v ep		USB endpoint
  * @v iobuf		I/O buffer
- * @v terminate		Terminate using a short packet
+ * @v zlp		Append a zero-length packet
  * @ret rc		Return status code
  */
 static int uhci_endpoint_stream ( struct usb_endpoint *ep,
-				  struct io_buffer *iobuf, int terminate ) {
+				  struct io_buffer *iobuf, int zlp ) {
 	struct uhci_endpoint *endpoint = usb_endpoint_get_hostdata ( ep );
 	struct uhci_ring *ring = &endpoint->ring;
 	unsigned int count;
 	size_t len;
 	int input;
-	int zlp;
 	int rc;
 
 	/* Calculate number of descriptors */
 	len = iob_len ( iobuf );
-	zlp = ( terminate && ( ( len & ( ring->mtu - 1 ) ) == 0 ) );
 	count = ( ( ( len + ring->mtu - 1 ) / ring->mtu ) + ( zlp ? 1 : 0 ) );
 
 	/* Enqueue transfer */

src/drivers/usb/usbio.c

  *
  * @v ep		USB endpoint
  * @v iobuf		I/O buffer
- * @v terminate		Terminate using a short packet
+ * @v zlp		Append a zero-length packet
  * @ret rc		Return status code
  */
 static int usbio_endpoint_stream ( struct usb_endpoint *ep,
-				   struct io_buffer *iobuf, int terminate ) {
-	size_t len = iob_len ( iobuf );
-	int zlen;
+				   struct io_buffer *iobuf, int zlp ) {
 
 	/* Enqueue transfer */
-	zlen = ( terminate && ( ( len & ( ep->mtu - 1 ) ) == 0 ) );
-	return usbio_endpoint_enqueue ( ep, iobuf, ( zlen ? USBIO_ZLEN : 0 ) );
+	return usbio_endpoint_enqueue ( ep, iobuf, ( zlp ? USBIO_ZLEN : 0 ) );
 }
 
 /**

src/drivers/usb/xhci.c

  *
  * @v ep		USB endpoint
  * @v iobuf		I/O buffer
- * @v terminate		Terminate using a short packet
+ * @v zlp		Append a zero-length packet
  * @ret rc		Return status code
  */
 static int xhci_endpoint_stream ( struct usb_endpoint *ep,
-				  struct io_buffer *iobuf, int terminate ) {
+				  struct io_buffer *iobuf, int zlp ) {
 	struct xhci_endpoint *endpoint = usb_endpoint_get_hostdata ( ep );
 	union xhci_trb trbs[ 1 /* Normal */ + 1 /* Possible zero-length */ ];
 	union xhci_trb *trb = trbs;
 	normal->data = cpu_to_le64 ( virt_to_phys ( iobuf->data ) );
 	normal->len = cpu_to_le32 ( len );
 	normal->type = XHCI_TRB_NORMAL;
-	if ( terminate && ( ( len & ( ep->mtu - 1 ) ) == 0 ) ) {
+	if ( zlp ) {
 		normal->flags = XHCI_TRB_CH;
 		normal = &(trb++)->normal;
 		normal->type = XHCI_TRB_NORMAL;

src/include/ipxe/usb.h

 	 *
 	 * @v ep		USB endpoint
 	 * @v iobuf		I/O buffer
-	 * @v terminate		Terminate using a short packet
+	 * @v zlp		Append a zero-length packet
 	 * @ret rc		Return status code
 	 */
 	int ( * stream ) ( struct usb_endpoint *ep, struct io_buffer *iobuf,
-			   int terminate );
+			   int zlp );
 };
 
 /** USB endpoint driver operations */