usb: dwc3: workaround: missing disconnect event

DWC3 revisions <1.88a have an issue which would
case a missing Disconnect event if cable is
disconnected while there's a Setup packet
pending the FIFO.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/core.h

@@ -578,6 +578,7 @@ struct dwc3_hwparams {
  * @ep0_bounced: true when we used bounce buffer
  * @ep0_expect_in: true when we expect a DATA IN transfer
  * @start_config_issued: true when StartConfig command has been issued
+ * @setup_packet_pending: true when there's a Setup Packet in FIFO. Workaround
  * @ep0_next_event: hold the next expected event
  * @ep0state: state of endpoint zero
  * @link_state: link state
@@ -633,6 +634,7 @@ struct dwc3 {
 	unsigned		ep0_bounced:1;
 	unsigned		ep0_expect_in:1;
 	unsigned		start_config_issued:1;
+	unsigned		setup_packet_pending:1;
 	unsigned		delayed_status:1;
 
 	enum dwc3_ep0_next	ep0_next_event;

drivers/usb/dwc3/ep0.c

@@ -625,6 +625,7 @@ static void dwc3_ep0_xfer_complete(struct dwc3 *dwc,
 	struct dwc3_ep		*dep = dwc->eps[event->endpoint_number];
 
 	dep->flags &= ~DWC3_EP_BUSY;
+	dwc->setup_packet_pending = false;
 
 	switch (dwc->ep0state) {
 	case EP0_SETUP_PHASE:
@@ -726,6 +727,8 @@ static void dwc3_ep0_do_control_status(struct dwc3 *dwc, u32 epnum)
 static void dwc3_ep0_xfernotready(struct dwc3 *dwc,
 		const struct dwc3_event_depevt *event)
 {
+	dwc->setup_packet_pending = true;
+
 	/*
 	 * This part is very tricky: If we has just handled
 	 * XferNotReady(Setup) and we're now expecting a

drivers/usb/dwc3/gadget.c

@@ -1640,6 +1640,7 @@ static void dwc3_gadget_disconnect_interrupt(struct dwc3 *dwc)
 	dwc->start_config_issued = false;
 
 	dwc->gadget.speed = USB_SPEED_UNKNOWN;
+	dwc->setup_packet_pending = false;
 }
 
 static void dwc3_gadget_usb3_phy_power(struct dwc3 *dwc, int on)
@@ -1676,6 +1677,37 @@ static void dwc3_gadget_reset_interrupt(struct dwc3 *dwc)
 
 	dev_vdbg(dwc->dev, "%s\n", __func__);
 
+	/*
+	 * WORKAROUND: DWC3 revisions <1.88a have an issue which
+	 * would cause a missing Disconnect Event if there's a
+	 * pending Setup Packet in the FIFO.
+	 *
+	 * There's no suggested workaround on the official Bug
+	 * report, which states that "unless the driver/application
+	 * is doing any special handling of a disconnect event,
+	 * there is no functional issue".
+	 *
+	 * Unfortunately, it turns out that we _do_ some special
+	 * handling of a disconnect event, namely complete all
+	 * pending transfers, notify gadget driver of the
+	 * disconnection, and so on.
+	 *
+	 * Our suggested workaround is to follow the Disconnect
+	 * Event steps here, instead, based on a setup_packet_pending
+	 * flag. Such flag gets set whenever we have a XferNotReady
+	 * event on EP0 and gets cleared on XferComplete for the
+	 * same endpoint.
+	 *
+	 * Refers to:
+	 *
+	 * STAR#9000466709: RTL: Device : Disconnect event not
+	 * generated if setup packet pending in FIFO
+	 */
+	if (dwc->revision < DWC3_REVISION_188A) {
+		if (dwc->setup_packet_pending)
+			dwc3_gadget_disconnect_interrupt(dwc);
+	}
+
 	/* Enable PHYs */
 	dwc3_gadget_usb2_phy_power(dwc, true);
 	dwc3_gadget_usb3_phy_power(dwc, true);