usb: dwc3: gadget: Remove END_TRANSFER delay

We had a 100us delay to synchronize the END_TRANSFER command completion
before giving back requests to the function drivers. Now, the controller
driver can handle cancelled TRBs with the requests' cancelled_list and
it can also wait until the END_TRANSFER completion before starting new
transfers. Synchronization can simply base on the controller's command
completion interrupt. The 100us delay is no longer needed. Remove this
arbitrary delay.
Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/gadget.c

@@ -2693,7 +2693,6 @@ static void dwc3_reset_gadget(struct dwc3 *dwc)
 static void dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force,
 	bool interrupt)
 {
-	struct dwc3 *dwc = dep->dwc;
 	struct dwc3_gadget_ep_cmd_params params;
 	u32 cmd;
 	int ret;
@@ -2709,16 +2708,13 @@ static void dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force,
 	 * much trouble synchronizing between us and gadget driver.
 	 *
 	 * We have discussed this with the IP Provider and it was
-	 * suggested to giveback all requests here, but give HW some
-	 * extra time to synchronize with the interconnect. We're using
-	 * an arbitrary 100us delay for that.
+	 * suggested to giveback all requests here.
 	 *
 	 * Note also that a similar handling was tested by Synopsys
 	 * (thanks a lot Paul) and nothing bad has come out of it.
-	 * In short, what we're doing is:
-	 *
-	 * - Issue EndTransfer WITH CMDIOC bit set
-	 * - Wait 100us
+	 * In short, what we're doing is issuing EndTransfer with
+	 * CMDIOC bit set and delay kicking transfer until the
+	 * EndTransfer command had completed.
 	 *
 	 * As of IP version 3.10a of the DWC_usb3 IP, the controller
 	 * supports a mode to work around the above limitation. The
@@ -2727,8 +2723,7 @@ static void dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force,
 	 * by writing GUCTL2[14]. This polling is already done in the
 	 * dwc3_send_gadget_ep_cmd() function so if the mode is
 	 * enabled, the EndTransfer command will have completed upon
-	 * returning from this function and we don't need to delay for
-	 * 100us.
+	 * returning from this function.
 	 *
 	 * This mode is NOT available on the DWC_usb31 IP.
 	 */
@@ -2746,9 +2741,6 @@ static void dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force,
 		dep->flags &= ~DWC3_EP_TRANSFER_STARTED;
 	else
 		dep->flags |= DWC3_EP_END_TRANSFER_PENDING;
-
-	if (dwc3_is_usb31(dwc) || dwc->revision < DWC3_REVISION_310A)
-		udelay(100);
 }
 
 static void dwc3_clear_stall_all_ep(struct dwc3 *dwc)