xhci: Add tracing for xhci doorbell register writes

Trace when a register in the doorbell array is written,
both for host controller command doorbell and device doorbells,
including for which endpoint and stream

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/1573836603-10871-3-git-send-email-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci.h

@@ -2580,6 +2580,35 @@ static inline const char *xhci_decode_portsc(u32 portsc)
 	return str;
 }
 
+static inline const char *xhci_decode_doorbell(u32 slot, u32 doorbell)
+{
+	static char str[256];
+	u8 ep;
+	u16 stream;
+	int ret;
+
+	ep = (doorbell & 0xff);
+	stream = doorbell >> 16;
+
+	if (slot == 0) {
+		sprintf(str, "Command Ring %d", doorbell);
+		return str;
+	}
+	ret = sprintf(str, "Slot %d ", slot);
+	if (ep > 0 && ep < 32)
+		ret = sprintf(str + ret, "ep%d%s",
+			      ep / 2,
+			      ep % 2 ? "in" : "out");
+	else if (ep == 0 || ep < 248)
+		ret = sprintf(str + ret, "Reserved %d", ep);
+	else
+		ret = sprintf(str + ret, "Vendor Defined %d", ep);
+	if (stream)
+		ret = sprintf(str + ret, " Stream %d", stream);
+
+	return str;
+}
+
 static inline const char *xhci_ep_state_string(u8 state)
 {
 	switch (state) {