usb: gadget: atmel: tie wake lock to running clock

If the USB device is connected to a host, the CPU cannot be suspended or
else the USB device appears to be disconnected from the host's point of
view.  Only after a "USB suspend" state has been entered (as set by the
host) or the host is disconnected can the system safely be suspended: in
both these states, the clock is stopped.  As such, this patch associates
a "wake lock" with the running clock of the UDC to keep the system awake
as long as the host maintains the USB connection active.
Signed-off-by: Jonas Bonn <jonas@norrbonn.se>
CC: Cristian Birsan <cristian.birsan@microchip.com>
CC: Felipe Balbi <balbi@kernel.org>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Nicolas Ferre <nicolas.ferre@microchip.com>
CC: Alexandre Belloni <alexandre.belloni@bootlin.com>
CC: Ludovic Desroches <ludovic.desroches@microchip.com>
CC: linux-arm-kernel@lists.infradead.org
CC: linux-usb@vger.kernel.org
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/atmel_usba_udc.c

@@ -1856,6 +1856,8 @@ static int start_clock(struct usba_udc *udc)
 	if (udc->clocked)
 		return 0;
 
+	pm_stay_awake(&udc->pdev->dev);
+
 	ret = clk_prepare_enable(udc->pclk);
 	if (ret)
 		return ret;
@@ -1878,6 +1880,8 @@ static void stop_clock(struct usba_udc *udc)
 	clk_disable_unprepare(udc->pclk);
 
 	udc->clocked = false;
+
+	pm_relax(&udc->pdev->dev);
 }
 
 static int usba_start(struct usba_udc *udc)