usb: dwc3: gadget: don't wrap around the TRB poll on non-ISOC

If we have a non-ISOC endpoint, we will not have a Link TRB
pointing to the beginning of the TRB pool. On such endpoints,
we don't want to let the driver wrap around the TRB pool
otherwise controller will hang waiting for a valid TRB.

Cc: stable@vger.kernel.org
Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/gadget.c

@@ -826,13 +826,21 @@ static void dwc3_prepare_trbs(struct dwc3_ep *dep, bool starting)
 {
 	struct dwc3_request	*req, *n;
 	u32			trbs_left;
+	u32			max;
 	unsigned int		last_one = 0;
 
 	BUILD_BUG_ON_NOT_POWER_OF_2(DWC3_TRB_NUM);
 
 	/* the first request must not be queued */
 	trbs_left = (dep->busy_slot - dep->free_slot) & DWC3_TRB_MASK;
 
+	/* Can't wrap around on a non-isoc EP since there's no link TRB */
+	if (!usb_endpoint_xfer_isoc(dep->desc)) {
+		max = DWC3_TRB_NUM - (dep->free_slot & DWC3_TRB_MASK);
+		if (trbs_left > max)
+			trbs_left = max;
+	}
+
 	/*
 	 * If busy & slot are equal than it is either full or empty. If we are
 	 * starting to process requests then we are empty. Otherwise we are