[PATCH] usb: dwc3: gadget: Check for L1/L2/U3 for Start Transfer

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

The programming guide noted that the driver needs to verify if the link
state is in U0 before executing the Start Transfer command. If it's not
in U0, the driver needs to perform remote wakeup. This is not accurate.
If the link state is in U1/U2, then the controller will not respond to
link recovery request from DCTL.ULSTCHNGREQ. The Start Transfer command
will trigger a link recovery if it is in U1/U2. A clarification will be
added to the programming guide for all controller versions.

The current implementation shouldn't cause any functional issue. It may
occasionally report an invalid time out warning from failed link
recovery request. The driver will still go ahead with the Start Transfer
command if the remote wakeup fails. The new change only initiates remote
wakeup where it is needed, which is when the link state is in L1/L2/U3.

Cc: <stable@vger.kernel.org>
Fixes: c36d8e947a56 ("usb: dwc3: gadget: put link to U0 before Start Transfer")
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
---
 drivers/usb/dwc3/gadget.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 23de2a5a40d6..e259198aa241 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -310,13 +310,24 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned int cmd,
 	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);
-		if (link_state == DWC3_LINK_STATE_U1 ||
-		    link_state == DWC3_LINK_STATE_U2 ||
-		    link_state == DWC3_LINK_STATE_U3) {
+		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);
 			dev_WARN_ONCE(dwc->dev, ret, "wakeup failed --> %d\n",
 					ret);
+			break;
 		}
 	}
 

base-commit: e8d6336d9d7198013a7b307107908242a7a53b23
-- 
2.28.0