usb: dwc3: gadget: split __dwc3_gadget_kick_transfer()

To aid code readability, we're gonna split
__dwc3_gadget_kick_transfer() into its constituent
parts: scatter gather and linear buffers.

That way, it's easier to follow the code and focus
debug effort when one or the other fails.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -903,33 +903,15 @@ static u32 dwc3_calc_trbs_left(struct dwc3_ep *dep)
 	return dep->trb_dequeue - dep->trb_enqueue;
 }
 
-/*
- * dwc3_prepare_trbs - setup TRBs from requests
- * @dep: endpoint for which requests are being prepared
- *
- * The function goes through the requests list and sets up TRBs for the
- * transfers. The function returns once there are no more TRBs available or
- * it runs out of requests.
- */
-static void dwc3_prepare_trbs(struct dwc3_ep *dep)
+static void dwc3_prepare_one_trb_sg(struct dwc3_ep *dep,
+		struct dwc3_request *req, unsigned int trbs_left)
 {
-	struct dwc3_request	*req, *n;
-	u32			trbs_left;
-	unsigned int		last_one = 0;
-
-	BUILD_BUG_ON_NOT_POWER_OF_2(DWC3_TRB_NUM);
-
-	trbs_left = dwc3_calc_trbs_left(dep);
-
-	list_for_each_entry_safe(req, n, &dep->pending_list, list) {
-		unsigned	length;
-		dma_addr_t	dma;
-		last_one = false;
-
-		if (req->request.num_mapped_sgs > 0) {
 	struct usb_request *request = &req->request;
 	struct scatterlist *sg = request->sg;
 	struct scatterlist *s;
+	unsigned int	last = false;
+	unsigned int	length;
+	dma_addr_t	dma;
 	int		i;
 
 	for_each_sg(sg, s, request->num_mapped_sgs, i) {
@@ -940,45 +922,71 @@ static void dwc3_prepare_trbs(struct dwc3_ep *dep)
 
 		if (sg_is_last(s)) {
 			if (list_is_last(&req->list, &dep->pending_list))
-						last_one = true;
+				last = true;
 
 			chain = false;
 		}
 
-				trbs_left--;
 		if (!trbs_left)
-					last_one = true;
+			last = true;
 
-				if (last_one)
+		if (last)
 			chain = false;
 
 		dwc3_prepare_one_trb(dep, req, dma, length,
-						last_one, chain, i);
+				last, chain, i);
 
-				if (last_one)
+		if (last)
 			break;
 	}
+}
+
+static void dwc3_prepare_one_trb_linear(struct dwc3_ep *dep,
+		struct dwc3_request *req, unsigned int trbs_left)
+{
+	unsigned int	last = false;
+	unsigned int	length;
+	dma_addr_t	dma;
 
-			if (last_one)
-				break;
-		} else {
 	dma = req->request.dma;
 	length = req->request.length;
-			trbs_left--;
 
 	if (!trbs_left)
-				last_one = true;
+		last = true;
 
 	/* Is this the last request? */
 	if (list_is_last(&req->list, &dep->pending_list))
-				last_one = true;
+		last = true;
 
 	dwc3_prepare_one_trb(dep, req, dma, length,
-					last_one, false, 0);
+			last, false, 0);
+}
 
-			if (last_one)
-				break;
-		}
+/*
+ * dwc3_prepare_trbs - setup TRBs from requests
+ * @dep: endpoint for which requests are being prepared
+ *
+ * The function goes through the requests list and sets up TRBs for the
+ * transfers. The function returns once there are no more TRBs available or
+ * it runs out of requests.
+ */
+static void dwc3_prepare_trbs(struct dwc3_ep *dep)
+{
+	struct dwc3_request	*req, *n;
+	u32			trbs_left;
+
+	BUILD_BUG_ON_NOT_POWER_OF_2(DWC3_TRB_NUM);
+
+	trbs_left = dwc3_calc_trbs_left(dep);
+
+	list_for_each_entry_safe(req, n, &dep->pending_list, list) {
+		if (req->request.num_mapped_sgs > 0)
+			dwc3_prepare_one_trb_sg(dep, req, trbs_left--);
+		else
+			dwc3_prepare_one_trb_linear(dep, req, trbs_left--);
+
+		if (!trbs_left)
+			return;
 	}
 }