usb: dwc3: core: add fifo space helper

this helper will be used, initially, to dump space
of different queues and fifos in dwc3 to
debugfs. Later, it'll be used to issue remote wakeup
when we want to start a transfer and there's
something in a TX FIFO.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 6f57929..c050a88 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -60,6 +60,20 @@
 	dwc3_writel(dwc->regs, DWC3_GCTL, reg);
 }
 
+u32 dwc3_core_fifo_space(struct dwc3_ep *dep, u8 type)
+{
+	struct dwc3		*dwc = dep->dwc;
+	u32			reg;
+
+	dwc3_writel(dwc->regs, DWC3_GDBGFIFOSPACE,
+			DWC3_GDBGFIFOSPACE_NUM(dep->number) |
+			DWC3_GDBGFIFOSPACE_TYPE(type));
+
+	reg = dwc3_readl(dwc->regs, DWC3_GDBGFIFOSPACE);
+
+	return DWC3_GDBGFIFOSPACE_SPACE_AVAILABLE(reg);
+}
+
 /**
  * dwc3_core_soft_reset - Issues core soft reset and PHY reset
  * @dwc: pointer to our context structure