usb: dwc3: core: add a event buffer cache

This extra buffer will be used so we can copy
triggered events from our event buffer to this cache
and process all of them later in bottom half
handler.

We need this in order to implement a workaround for
a known erratum in recent DWC3 release.
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/core.c

@@ -224,6 +224,10 @@ static struct dwc3_event_buffer *dwc3_alloc_one_event_buffer(struct dwc3 *dwc,
 
 	evt->dwc	= dwc;
 	evt->length	= length;
+	evt->cache	= devm_kzalloc(dwc->dev, length, GFP_KERNEL);
+	if (!evt->cache)
+		return ERR_PTR(-ENOMEM);
+
 	evt->buf	= dma_alloc_coherent(dwc->dev, length,
 			&evt->dma, GFP_KERNEL);
 	if (!evt->buf)

drivers/usb/dwc3/core.h

@@ -472,6 +472,7 @@ struct dwc3_trb;
 /**
  * struct dwc3_event_buffer - Software event buffer representation
  * @buf: _THE_ buffer
+ * @cache: The buffer cache used in the threaded interrupt
  * @length: size of this buffer
  * @lpos: event offset
  * @count: cache of last read event count register
@@ -481,6 +482,7 @@ struct dwc3_trb;
  */
 struct dwc3_event_buffer {
 	void			*buf;
+	void			*cache;
 	unsigned		length;
 	unsigned int		lpos;
 	unsigned int		count;