--- a/configure.ac	Sat May 31 14:49:02 2014 +1200
+++ b/configure.ac	Sat May 31 15:37:33 2014 +1200
@@ -820,6 +820,35 @@
 fi
 
 #------------------------------------------------------------------------------
+# Force the reference clock to OP even if unconfigured
+#------------------------------------------------------------------------------
+
+AC_MSG_CHECKING([whether to force the reference clock to OP])
+
+AC_ARG_ENABLE([refclkop],
+    AS_HELP_STRING([--enable-refclkop],
+                   [Force reference clock to OP (default: no)]),
+    [
+        case "${enableval}" in
+            yes) refclkop=1
+                ;;
+            no) refclkop=0
+                ;;
+            *) AC_MSG_ERROR([Invalid value for --enable-refclkop])
+                ;;
+        esac
+    ],
+    [refclkop=0]
+)
+
+if test "x${refclkop}" = "x1"; then
+    AC_DEFINE([EC_REFCLKOP], [1], [Force refclk to OP])
+    AC_MSG_RESULT([yes])
+else
+    AC_MSG_RESULT([no])
+fi
+
+#------------------------------------------------------------------------------
 # Command-line tool
 #-----------------------------------------------------------------------------
 

--- a/master/master.c	Sat May 31 14:49:02 2014 +1200
+++ b/master/master.c	Sat May 31 15:37:33 2014 +1200
@@ -2224,10 +2224,12 @@
         }
     }
 
+#ifdef EC_REFCLKOP
     // always set DC reference clock to OP
     if (master->dc_ref_clock) {
         ec_slave_request_state(master->dc_ref_clock, EC_SLAVE_STATE_OP);
     }
+#endif
 }
 
 /******************************************************************************