usb: cdns3: improve handling of unaligned address case

When the address of a request was not aligned with an 8-byte boundary, the
USB DMA was unable to process it, necessitating the use of an internal
bounce buffer.

In these cases, the request->buf had to be copied to/from this bounce
buffer. However, if this unaligned address scenario arises, it is
unnecessary to perform heavy cache maintenance operations like
usb_gadget_map(unmap)_request_by_dev() on the request->buf, as the DMA
does not utilize it at all. it can be skipped at this case.

iperf3 tests on the rndis case:

Transmit speed (TX): Improved from 299Mbps to 440Mbps
Receive speed (RX): Improved from 290Mbps to 500Mbps
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20230518204947.3770236-1-Frank.Li@nxp.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/cdns3/cdns3-gadget.c

@@ -800,7 +800,8 @@ void cdns3_gadget_giveback(struct cdns3_endpoint *priv_ep,
 	if (request->status == -EINPROGRESS)
 		request->status = status;
 
-	usb_gadget_unmap_request_by_dev(priv_dev->sysdev, request,
+	if (likely(!(priv_req->flags & REQUEST_UNALIGNED)))
+		usb_gadget_unmap_request_by_dev(priv_dev->sysdev, request,
 					priv_ep->dir);
 
 	if ((priv_req->flags & REQUEST_UNALIGNED) &&
@@ -2530,10 +2531,12 @@ static int __cdns3_gadget_ep_queue(struct usb_ep *ep,
 	if (ret < 0)
 		return ret;
 
-	ret = usb_gadget_map_request_by_dev(priv_dev->sysdev, request,
+	if (likely(!(priv_req->flags & REQUEST_UNALIGNED))) {
+		ret = usb_gadget_map_request_by_dev(priv_dev->sysdev, request,
 					    usb_endpoint_dir_in(ep->desc));
-	if (ret)
-		return ret;
+		if (ret)
+			return ret;
+	}
 
 	list_add_tail(&request->list, &priv_ep->deferred_req_list);