usb: dwc3: gadget: use evt->cache for processing events

Let's start copying events from evt->buf to
evt->cache and use evt->cache for processing events.

A follow-up patch will be added to clear events in
the top-half handler in order to bring IRQ line low
as soon as possible.
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -2821,7 +2821,7 @@ static irqreturn_t dwc3_process_event_buf(struct dwc3_event_buffer *evt)
 	while (left > 0) {
 		union dwc3_event event;
 
-		event.raw = *(u32 *) (evt->buf + evt->lpos);
+		event.raw = *(u32 *) (evt->cache + evt->lpos);
 
 		dwc3_process_event_entry(dwc, &event);
 
@@ -2869,6 +2869,7 @@ static irqreturn_t dwc3_thread_interrupt(int irq, void *_evt)
 static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
 {
 	struct dwc3 *dwc = evt->dwc;
+	u32 amount;
 	u32 count;
 	u32 reg;
 
@@ -2892,6 +2893,12 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
 	reg |= DWC3_GEVNTSIZ_INTMASK;
 	dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0), reg);
 
+	amount = min(count, evt->length - evt->lpos);
+	memcpy(evt->cache + evt->lpos, evt->buf + evt->lpos, amount);
+
+	if (amount < count)
+		memcpy(evt->cache, evt->buf, count - amount);
+
 	return IRQ_WAKE_THREAD;
 }