linux-explicit-synchronization: Warn about using the protocol while u…

…sing graphics APIs

Graphics APIs are expected to use this protocol under the hood, and
since there can only be one user of explicit synchronization per
surface, warn about using the protocol directly in such cases.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>

unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml

@@ -66,6 +66,12 @@
 
         If the given wl_surface already has an explicit synchronization object
         associated, the synchronization_exists protocol error is raised.
+
+        Graphics APIs, like EGL or Vulkan, that manage the buffer queue and
+        commits of a wl_surface themselves, are likely to be using this
+        extension internally. If a client is using such an API for a
+        wl_surface, it should not directly use this extension on that surface,
+        to avoid raising a synchronization_exists protocol error.
       </description>
 
       <arg name="id" type="new_id"