usb: dwc2: Problem with remote wakeup implementation

[Maxim Devaev <mdevaev@gmail.com>]

Hello. I'm trying to implement remote wakeup signalling for dwc2.
The dwc3 driver in gadget mode has the ability to send a remote
wakeup signal to the host by writing 1 to the srp file:

echo 1 > /sys/class/udc/XXX/srp

My naive implementation was able to wake up the host on 5.10 kernel,
but it's not working anymore on 5.15, it's just does nothing now.
I tried to roll back all the changes in drivers/usb/dwc2 to the 5.10,
but it didn't help.

I don't have any DesignWare documentation, so I hope someone
can help me to make it work in the right way.

I will be very grateful.


diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
index 3146df6e6510..c64e573af7ca 100644
--- a/drivers/usb/dwc2/gadget.c
+++ b/drivers/usb/dwc2/gadget.c
@@ -4683,6 +4683,52 @@ static int dwc2_hsotg_vbus_draw(struct usb_gadget *gadget, unsigned int mA)
 	return usb_phy_set_power(hsotg->uphy, mA);
 }
 
+/**
+ * dwc2_hsotg_wakeup - send wakeup signal to the host
+ * @gadget: The usb gadget state
+ *
+ * If the gadget is in device mode and in the L1 or L2 state,
+ * it sends a wakeup signal to the host.
+ */
+static int dwc2_hsotg_wakeup(struct usb_gadget *gadget)
+{
+	struct dwc2_hsotg *hsotg = to_hsotg(gadget);
+	int ret = -1;
+	unsigned long flags;
+
+	spin_lock_irqsave(&hsotg->lock, flags);
+
+	if (!hsotg->remote_wakeup_allowed) {
+		dev_dbg(hsotg->dev,
+			"wakeup signalling skipped: is not allowed by host\n");
+		goto skip;
+	}
+	if (hsotg->lx_state != DWC2_L1 && hsotg->lx_state != DWC2_L2) {
+		dev_dbg(hsotg->dev,
+			"wakeup signalling skipped: gadget not in L1/L2 state\n");
+		goto skip;
+	}
+	if (!dwc2_is_device_mode(hsotg)) {
+		dev_dbg(hsotg->dev,
+			"wakeup signalling skipped: gadget not in device mode\n");
+		goto skip;
+	}
+
+	dev_dbg(hsotg->dev, "sending wakeup signal to the host");
+
+	dwc2_set_bit(hsotg, DCTL, DCTL_RMTWKUPSIG);
+	mdelay(10);
+	dwc2_clear_bit(hsotg, DCTL, DCTL_RMTWKUPSIG);
+
+	/* After the signalling, the USB core wakes up to L0 */
+	hsotg->lx_state = DWC2_L0;
+
+	ret = 0;
+skip:
+	spin_unlock_irqrestore(&hsotg->lock, flags);
+	return ret;
+}
+
 static const struct usb_gadget_ops dwc2_hsotg_gadget_ops = {
 	.get_frame	= dwc2_hsotg_gadget_getframe,
 	.set_selfpowered	= dwc2_hsotg_set_selfpowered,
@@ -4691,6 +4737,7 @@ static const struct usb_gadget_ops dwc2_hsotg_gadget_ops = {
 	.pullup                 = dwc2_hsotg_pullup,
 	.vbus_session		= dwc2_hsotg_vbus_session,
 	.vbus_draw		= dwc2_hsotg_vbus_draw,
+	.wakeup			= dwc2_hsotg_wakeup,
 };
 
 /**