usb: dwc3: gadget: Fix checking for number of TRBs left

The check whether the TRB ring is full or empty in dwc3_calc_trbs_left()
is insufficient. It assumes there are active TRBs if there's any request
in the started_list. However, that's not the case for requests with a
large SG list.

That is, if we have a single usb request that requires more TRBs than
the total TRBs in the TRB ring, the queued TRBs will be available when
all the TRBs in the ring are completed. But the request is only
partially completed and remains in the started_list. With the current
logic, the TRB ring is empty, but dwc3_calc_trbs_left() returns 0.

Fix this by additionally checking for the request->num_trbs for active
TRB count.

Cc: [email protected]
Fixes: 51f1954 ("usb: dwc3: gadget: Fix dwc3_calc_trbs_left()")
Signed-off-by: Thinh Nguyen <[email protected]>
Link: https://lore.kernel.org/r/708dc62b56b77da1f704cc2ae9b6ddb1f2dbef1f.1731545781.git.Thinh.Nguyen@synopsys.com
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Thinh Nguyen

drivers/usb/dwc3/gadget.c

@@ -1230,11 +1230,14 @@ static u32 dwc3_calc_trbs_left(struct dwc3_ep *dep)
 	 * pending to be processed by the driver.
 	 */
 	if (dep->trb_enqueue == dep->trb_dequeue) {
+		struct dwc3_request *req;
+
 		/*
-		 * If there is any request remained in the started_list at
-		 * this point, that means there is no TRB available.
+		 * If there is any request remained in the started_list with
+		 * active TRBs at this point, then there is no TRB available.
 		 */
-		if (!list_empty(&dep->started_list))
+		req = next_request(&dep->started_list);
+		if (req && req->num_trbs)
 			return 0;
 
 		return DWC3_TRB_NUM - 1;