usb: dwc3: gadget: cope with XferNotReady before usb_ep_queue()

If XferNotReady comes before usb_ep_queue() we will
set our PENDING request flag and wait for a
request. However, originally, we were assuming
usb_ep_queue() would always happen before our first
XferNotReady and that causes a corner case where we
could try to issue ENDTRANSFER command before
STARTTRANSFER.

Let's fix that by tracking endpoints which have been
started.
Reported-by: Janusz Dziedzic <januszx.dziedzic@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/core.h

@@ -551,6 +551,7 @@ struct dwc3_ep {
 #define DWC3_EP_PENDING_REQUEST	(1 << 5)
 #define DWC3_EP_MISSED_ISOC	(1 << 6)
 #define DWC3_EP_END_TRANSFER_PENDING	(1 << 7)
+#define DWC3_EP_TRANSFER_STARTED (1 << 8)
 
 	/* This last one is specific to EP0 */
 #define DWC3_EP0_DIR_IN		(1 << 31)

drivers/usb/dwc3/gadget.c

@@ -340,6 +340,20 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned cmd,
 
 	trace_dwc3_gadget_ep_cmd(dep, cmd, params, cmd_status);
 
+	if (ret == 0) {
+		switch (DWC3_DEPCMD_CMD(cmd)) {
+		case DWC3_DEPCMD_STARTTRANSFER:
+			dep->flags |= DWC3_EP_TRANSFER_STARTED;
+			break;
+		case DWC3_DEPCMD_ENDTRANSFER:
+			dep->flags &= ~DWC3_EP_TRANSFER_STARTED;
+			break;
+		default:
+			/* nothing */
+			break;
+		}
+	}
+
 	if (unlikely(susphy)) {
 		reg = dwc3_readl(dwc->regs, DWC3_GUSB2PHYCFG(0));
 		reg |= DWC3_GUSB2PHYCFG_SUSPHY;
@@ -1066,6 +1080,14 @@ static int __dwc3_gadget_kick_transfer(struct dwc3_ep *dep, u16 cmd_param)
 	return 0;
 }
 
+static int __dwc3_gadget_get_frame(struct dwc3 *dwc)
+{
+	u32			reg;
+
+	reg = dwc3_readl(dwc->regs, DWC3_DSTS);
+	return DWC3_DSTS_SOFFN(reg);
+}
+
 static void __dwc3_gadget_start_isoc(struct dwc3 *dwc,
 		struct dwc3_ep *dep, u32 cur_uf)
 {
@@ -1143,10 +1165,16 @@ static int __dwc3_gadget_ep_queue(struct dwc3_ep *dep, struct dwc3_request *req)
 	 * errors which will force us issue EndTransfer command.
 	 */
 	if (usb_endpoint_xfer_isoc(dep->endpoint.desc)) {
-		if ((dep->flags & DWC3_EP_PENDING_REQUEST) &&
-				list_empty(&dep->started_list)) {
-			dwc3_stop_active_transfer(dwc, dep->number, true);
-			dep->flags = DWC3_EP_ENABLED;
+		if ((dep->flags & DWC3_EP_PENDING_REQUEST)) {
+			if (dep->flags & DWC3_EP_TRANSFER_STARTED) {
+				dwc3_stop_active_transfer(dwc, dep->number, true);
+				dep->flags = DWC3_EP_ENABLED;
+			} else {
+				u32 cur_uf;
+
+				cur_uf = __dwc3_gadget_get_frame(dwc);
+				__dwc3_gadget_start_isoc(dwc, dep, cur_uf);
+			}
 		}
 		return 0;
 	}
@@ -1392,10 +1420,8 @@ static const struct usb_ep_ops dwc3_gadget_ep_ops = {
 static int dwc3_gadget_get_frame(struct usb_gadget *g)
 {
 	struct dwc3		*dwc = gadget_to_dwc(g);
-	u32			reg;
 
-	reg = dwc3_readl(dwc->regs, DWC3_DSTS);
-	return DWC3_DSTS_SOFFN(reg);
+	return __dwc3_gadget_get_frame(dwc);
 }
 
 static int __dwc3_gadget_wakeup(struct dwc3 *dwc)