input: prevent the caller from sleeping in sysworkq

Sleeping in sysworkq is a very bad idea, it can trash any hope of
realtimeness at best, deadlock the whole system at worse.

Add a check to input_report to downgrade the event to K_NO_WAIT
automatically when called from the sysworkq, similarly to what's done by
other APIs (netbuf and bluetooth), though only log if messages are
actually dropped.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

subsys/input/input.c

@@ -50,7 +50,21 @@ int input_report(const struct device *dev,
 	};
 
 #ifdef CONFIG_INPUT_MODE_THREAD
-	return k_msgq_put(&input_msgq, &evt, timeout);
+	int ret;
+
+	if (!K_TIMEOUT_EQ(timeout, K_NO_WAIT) &&
+	    k_current_get() == k_work_queue_thread_get(&k_sys_work_q)) {
+		LOG_DBG("Timeout discarded. No blocking in syswq.");
+		timeout = K_NO_WAIT;
+	}
+
+	ret = k_msgq_put(&input_msgq, &evt, timeout);
+	if (ret < 0) {
+		LOG_WRN("Event dropped, queue full, not blocking in syswq.");
+		return ret;
+	}
+
+	return 0;
 #else
 	input_process(&evt);
 	return 0;