usb: dwc3: gadget: fix for short pkts during chained xfers

DWC3 has one interesting peculiarity with chained
transfers. If we setup N chained transfers and we
get a short packet before processing all N TRBs,
DWC3 will (conditionally) issue a XferComplete or
XferInProgress event and retire all TRBs from the
one which got a short packet to the last without
clearing their HWO bits.

This means SW must clear HWO bit manually, which
this patch is doing.

Cc: <stable@vger.kernel.org>
Cc: Brian E Rogers <brian.e.rogers@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -1955,7 +1955,8 @@ static void dwc3_gadget_free_endpoints(struct dwc3 *dwc)
 
 static int __dwc3_cleanup_done_trbs(struct dwc3 *dwc, struct dwc3_ep *dep,
 		struct dwc3_request *req, struct dwc3_trb *trb,
-		const struct dwc3_event_depevt *event, int status)
+		const struct dwc3_event_depevt *event, int status,
+		int chain)
 {
 	unsigned int		count;
 	unsigned int		s_pkt = 0;
@@ -1964,6 +1965,19 @@ static int __dwc3_cleanup_done_trbs(struct dwc3 *dwc, struct dwc3_ep *dep,
 	dep->queued_requests--;
 	trace_dwc3_complete_trb(dep, trb);
 
+	/*
+	 * If we're in the middle of series of chained TRBs and we
+	 * receive a short transfer along the way, DWC3 will skip
+	 * through all TRBs including the last TRB in the chain (the
+	 * where CHN bit is zero. DWC3 will also avoid clearing HWO
+	 * bit and SW has to do it manually.
+	 *
+	 * We're going to do that here to avoid problems of HW trying
+	 * to use bogus TRBs for transfers.
+	 */
+	if (chain && (trb->ctrl & DWC3_TRB_CTRL_HWO))
+		trb->ctrl &= ~DWC3_TRB_CTRL_HWO;
+
 	if ((trb->ctrl & DWC3_TRB_CTRL_HWO) && status != -ESHUTDOWN)
 		/*
 		 * We continue despite the error. There is not much we
@@ -1975,6 +1989,7 @@ static int __dwc3_cleanup_done_trbs(struct dwc3 *dwc, struct dwc3_ep *dep,
 		 */
 		dev_err(dwc->dev, "%s's TRB (%p) still owned by HW\n",
 				dep->name, trb);
+
 	count = trb->size & DWC3_TRB_SIZE_MASK;
 
 	if (dep->direction) {
@@ -2036,10 +2051,13 @@ static int dwc3_cleanup_done_reqs(struct dwc3 *dwc, struct dwc3_ep *dep,
 	int			ret;
 
 	do {
+		int chain;
+
 		req = next_request(&dep->started_list);
 		if (WARN_ON_ONCE(!req))
 			return 1;
 
+		chain = req->request.num_mapped_sgs > 0;
 		i = 0;
 		do {
 			slot = req->first_trb_index + i;
@@ -2049,9 +2067,8 @@ static int dwc3_cleanup_done_reqs(struct dwc3 *dwc, struct dwc3_ep *dep,
 			trb = &dep->trb_pool[slot];
 			count += trb->size & DWC3_TRB_SIZE_MASK;
 
-
 			ret = __dwc3_cleanup_done_trbs(dwc, dep, req, trb,
-					event, status);
+					event, status, chain);
 			if (ret)
 				break;
 		} while (++i < req->request.num_mapped_sgs);