usb: dwc3: gadget: Avoid starting DWC3 gadget during UDC unbind

There is a race present where the DWC3 runtime resume runs in parallel
to the UDC unbind sequence.  This will eventually lead to a possible
scenario where we are enabling the run/stop bit, without a valid
composition defined.

Thread#1 (handling UDC unbind):
usb_gadget_remove_driver()
-->usb_gadget_disconnect()
  -->dwc3_gadget_pullup(0)
--> continue UDC unbind sequence
-->Thread#2 is running in parallel here

Thread#2 (handing next cable connect)
__dwc3_set_mode()
  -->pm_runtime_get_sync()
    -->dwc3_gadget_resume()
      -->dwc->gadget_driver is NOT NULL yet
      -->dwc3_gadget_run_stop(1)
      --> _dwc3gadget_start()
...

Fix this by tracking the pullup disable routine, and avoiding resuming
of the DWC3 gadget.  Once the UDC is re-binded, that will trigger the
pullup enable routine, which would handle enabling the DWC3 gadget.

Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
Link: https://lore.kernel.org/r/20210917021852.2037-1-wcheng@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/core.h

@@ -1032,6 +1032,7 @@ struct dwc3_scratchpad_array {
  * @tx_fifo_resize_max_num: max number of fifos allocated during txfifo resize
  * @hsphy_interface: "utmi" or "ulpi"
  * @connected: true when we're connected to a host, false otherwise
+ * @softconnect: true when gadget connect is called, false when disconnect runs
  * @delayed_status: true when gadget driver asks for delayed status
  * @ep0_bounced: true when we used bounce buffer
  * @ep0_expect_in: true when we expect a DATA IN transfer
@@ -1252,6 +1253,7 @@ struct dwc3 {
 	const char		*hsphy_interface;
 
 	unsigned		connected:1;
+	unsigned		softconnect:1;
 	unsigned		delayed_status:1;
 	unsigned		ep0_bounced:1;
 	unsigned		ep0_expect_in:1;

drivers/usb/dwc3/gadget.c

@@ -2418,7 +2418,7 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
 	int			ret;
 
 	is_on = !!is_on;
-
+	dwc->softconnect = is_on;
 	/*
 	 * Per databook, when we want to stop the gadget, if a control transfer
 	 * is still in process, complete it and get the core into setup phase.
@@ -4352,7 +4352,7 @@ int dwc3_gadget_resume(struct dwc3 *dwc)
 {
 	int			ret;
 
-	if (!dwc->gadget_driver)
+	if (!dwc->gadget_driver || !dwc->softconnect)
 		return 0;
 
 	ret = __dwc3_gadget_start(dwc);