firmware: arm_scmi: Fix handling of unexpected delayed responses

Upon reception of an unexpected bogus delayed response, clear the channel
and bail-out safely.

Link: https://lore.kernel.org/r/20200420152315.21008-5-cristian.marussi@arm.com
Fixes: 4d09852 ("firmware: arm_scmi: Add support for notifications message processing")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/driver.c

@@ -247,6 +247,21 @@ static void scmi_handle_response(struct scmi_chan_info *cinfo,
 	}
 
 	xfer = &minfo->xfer_block[xfer_id];
+	/*
+	 * Even if a response was indeed expected on this slot at this point,
+	 * a buggy platform could wrongly reply feeding us an unexpected
+	 * delayed response we're not prepared to handle: bail-out safely
+	 * blaming firmware.
+	 */
+	if (unlikely(msg_type == MSG_TYPE_DELAYED_RESP && !xfer->async_done)) {
+		dev_err(dev,
+			"Delayed Response for %d not expected! Buggy F/W ?\n",
+			xfer_id);
+		info->desc->ops->clear_channel(cinfo);
+		/* It was unexpected, so nobody will clear the xfer if not us */
+		__scmi_xfer_put(minfo, xfer);
+		return;
+	}
 
 	scmi_dump_header_dbg(dev, &xfer->hdr);