diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index f6cb5c0163..26a455975b 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -8497,6 +8497,12 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
                     configuration file (i.e.
                     <filename>conf/machine/&lt;machine_name&gt;.conf</filename>).
                 </para>
+
+                <para>
+                    Please see the "Selection of Processor Architecture and
+                    Board Type" section in the U-Boot README for valid values
+                    for this variable.
+                </para>
             </glossdef>
         </glossentry>