usb: dwc3: Avoid waking up gadget during startxfer

When operating in High-Speed, it is observed that DSTS[USBLNKST] doesn't
update link state immediately after receiving the wakeup interrupt. Since
wakeup event handler calls the resume callbacks, there is a chance that
function drivers can perform an ep queue, which in turn tries to perform
remote wakeup from send_gadget_ep_cmd(STARTXFER). This happens because
DSTS[[21:18] wasn't updated to U0 yet, it's observed that the latency of
DSTS can be in order of milli-seconds. Hence avoid calling gadget_wakeup
during startxfer to prevent unnecessarily issuing remote wakeup to host.

Fixes: c36d8e9 ("usb: dwc3: gadget: put link to U0 before Start Transfer")
Cc: [email protected]
Suggested-by: Thinh Nguyen <[email protected]>
Signed-off-by: Prashanth K <[email protected]>
Acked-by: Thinh Nguyen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Prashanth K

drivers/usb/dwc3/gadget.c

@@ -287,6 +287,23 @@ static int __dwc3_gadget_wakeup(struct dwc3 *dwc, bool async);
  *
  * Caller should handle locking. This function will issue @cmd with given
  * @params to @dep and wait for its completion.
+ *
+ * According to the programming guide, if the link state is in L1/L2/U3,
+ * then sending the Start Transfer command may not complete. The
+ * programming guide suggested to bring the link state back to ON/U0 by
+ * performing remote wakeup prior to sending the command. However, don't
+ * initiate remote wakeup when the user/function does not send wakeup
+ * request via wakeup ops. Send the command when it's allowed.
+ *
+ * Notes:
+ * For L1 link state, issuing a command requires the clearing of
+ * GUSB2PHYCFG.SUSPENDUSB2, which turns on the signal required to complete
+ * the given command (usually within 50us). This should happen within the
+ * command timeout set by driver. No additional step is needed.
+ *
+ * For L2 or U3 link state, the gadget is in USB suspend. Care should be
+ * taken when sending Start Transfer command to ensure that it's done after
+ * USB resume.
  */
 int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned int cmd,
 		struct dwc3_gadget_ep_cmd_params *params)
@@ -327,30 +344,6 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned int cmd,
 			dwc3_writel(dwc->regs, DWC3_GUSB2PHYCFG(0), reg);
 	}
 
-	if (DWC3_DEPCMD_CMD(cmd) == DWC3_DEPCMD_STARTTRANSFER) {
-		int link_state;
-
-		/*
-		 * Initiate remote wakeup if the link state is in U3 when
-		 * operating in SS/SSP or L1/L2 when operating in HS/FS. If the
-		 * link state is in U1/U2, no remote wakeup is needed. The Start
-		 * Transfer command will initiate the link recovery.
-		 */
-		link_state = dwc3_gadget_get_link_state(dwc);
-		switch (link_state) {
-		case DWC3_LINK_STATE_U2:
-			if (dwc->gadget->speed >= USB_SPEED_SUPER)
-				break;
-
-			fallthrough;
-		case DWC3_LINK_STATE_U3:
-			ret = __dwc3_gadget_wakeup(dwc, false);
-			dev_WARN_ONCE(dwc->dev, ret, "wakeup failed --> %d\n",
-					ret);
-			break;
-		}
-	}
-
 	/*
 	 * For some commands such as Update Transfer command, DEPCMDPARn
 	 * registers are reserved. Since the driver often sends Update Transfer