posix: deprecate "nonblocking" method
diff --git a/serial/serialposix.py b/serial/serialposix.py
index 28164d8..bc2468c 100644
--- a/serial/serialposix.py
+++ b/serial/serialposix.py
@@ -635,12 +635,6 @@
         s = fcntl.ioctl(self.fd, TIOCOUTQ, TIOCM_zero_str)
         return struct.unpack('I', s)[0]
 
-    def nonblocking(self):
-        """internal - not portable!"""
-        if not self.is_open:
-            raise portNotOpenError
-        fcntl.fcntl(self.fd, fcntl.F_SETFL, os.O_NONBLOCK)
-
     def fileno(self):
         """\
         For easier use of the serial port instance with select.
@@ -676,6 +670,11 @@
         else:
             termios.tcflow(self.fd, termios.TCOOFF)
 
+    def nonblocking(self):
+        """DEPRECATED - has no use"""
+        import warnings
+        warnings.warn("nonblocking() has no effect, already nonblocking", DeprecationWarning)
+
 
 class PosixPollSerial(Serial):
     """\