kms/update: Add way to receive result from later posted update

Something might want to affect the next update that is going to be
posted, but without posting it immediately. For example, changing the
cursor might need to wait for mode setting. Make it possible to get
feedback from posting the update, in order to gracefully handle any
errors.

Note, the API for notifiying about results take out the result listener
from the update, and notifies them in an open coded for loop. The reason
for this is that in the next commit we'll sometimes reuse updates, and
we only want notify about the results once.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1488>

src/backends/native/meta-kms-update-private.h

@@ -93,6 +93,12 @@ typedef struct _MetaKmsPageFlipListener
   gpointer user_data;
 } MetaKmsPageFlipListener;
 
+typedef struct _MetaKmsResultListener
+{
+  MetaKmsResultListenerFunc func;
+  gpointer user_data;
+} MetaKmsResultListener;
+
 void meta_kms_plane_feedback_free (MetaKmsPlaneFeedback *plane_feedback);
 
 MetaKmsPlaneFeedback * meta_kms_plane_feedback_new_take_error (MetaKmsPlane *plane,
@@ -130,6 +136,13 @@ void meta_kms_update_get_custom_page_flip_func (MetaKmsUpdate             *updat
                                                 MetaKmsCustomPageFlipFunc *custom_page_flip_func,
                                                 gpointer                  *custom_page_flip_user_data);
 
+GList * meta_kms_update_take_result_listeners (MetaKmsUpdate *update);
+
+void meta_kms_result_listener_notify (MetaKmsResultListener *listener,
+                                      const MetaKmsFeedback *feedback);
+
+void meta_kms_result_listener_free (MetaKmsResultListener *listener);
+
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (MetaKmsPlaneFeedback,
                                meta_kms_plane_feedback_free)
 

src/backends/native/meta-kms-update.c

@@ -44,6 +44,7 @@ struct _MetaKmsUpdate
   gpointer custom_page_flip_user_data;
 
   GList *page_flip_listeners;
+  GList *result_listeners;
 };
 
 void
@@ -379,6 +380,42 @@ meta_kms_plane_assignment_set_cursor_hotspot (MetaKmsPlaneAssignment *plane_assi
   plane_assignment->cursor_hotspot.y = y;
 }
 
+void
+meta_kms_update_add_result_listener (MetaKmsUpdate             *update,
+                                     MetaKmsResultListenerFunc  func,
+                                     gpointer                   user_data)
+{
+  MetaKmsResultListener *listener;
+
+  listener = g_new0 (MetaKmsResultListener, 1);
+  *listener = (MetaKmsResultListener) {
+    .func = func,
+    .user_data = user_data,
+  };
+
+  update->result_listeners = g_list_append (update->result_listeners,
+                                            listener);
+}
+
+GList *
+meta_kms_update_take_result_listeners (MetaKmsUpdate *update)
+{
+  return g_steal_pointer (&update->result_listeners);
+}
+
+void
+meta_kms_result_listener_notify (MetaKmsResultListener *listener,
+                                 const MetaKmsFeedback *feedback)
+{
+  listener->func (feedback, listener->user_data);
+}
+
+void
+meta_kms_result_listener_free (MetaKmsResultListener *listener)
+{
+  g_free (listener);
+}
+
 MetaKmsPlaneAssignment *
 meta_kms_update_get_primary_plane_assignment (MetaKmsUpdate *update,
                                               MetaKmsCrtc   *crtc)
@@ -467,6 +504,8 @@ meta_kms_update_new (MetaKmsDevice *device)
 void
 meta_kms_update_free (MetaKmsUpdate *update)
 {
+  g_list_free_full (update->result_listeners,
+                    (GDestroyNotify) meta_kms_result_listener_free);
   g_list_free_full (update->plane_assignments,
                     (GDestroyNotify) meta_kms_plane_assignment_free);
   g_list_free_full (update->mode_sets,

src/backends/native/meta-kms-update.h

@@ -69,6 +69,9 @@ typedef struct _MetaKmsPlaneFeedback
   GError *error;
 } MetaKmsPlaneFeedback;
 
+typedef void (* MetaKmsResultListenerFunc) (const MetaKmsFeedback *feedback,
+                                            gpointer               user_data);
+
 void meta_kms_feedback_free (MetaKmsFeedback *feedback);
 
 MetaKmsFeedbackResult meta_kms_feedback_get_result (const MetaKmsFeedback *feedback);
@@ -130,6 +133,10 @@ void meta_kms_plane_assignment_set_cursor_hotspot (MetaKmsPlaneAssignment *plane
                                                    int                     x,
                                                    int                     y);
 
+void meta_kms_update_add_result_listener (MetaKmsUpdate             *update,
+                                          MetaKmsResultListenerFunc  func,
+                                          gpointer                   user_data);
+
 static inline MetaFixed16
 meta_fixed_16_from_int (int16_t d)
 {

src/backends/native/meta-kms.c

@@ -251,6 +251,8 @@ meta_kms_post_pending_update_sync (MetaKms       *kms,
 {
   MetaKmsUpdate *update;
   MetaKmsFeedback *feedback;
+  GList *result_listeners;
+  GList *l;
 
   COGL_TRACE_BEGIN_SCOPED (MetaKmsPostUpdateSync,
                            "KMS (post update)");
@@ -266,6 +268,17 @@ meta_kms_post_pending_update_sync (MetaKms       *kms,
                                           update,
                                           NULL);
 
+  result_listeners = meta_kms_update_take_result_listeners (update);
+
+  for (l = result_listeners; l; l = l->next)
+    {
+      MetaKmsResultListener *listener = l->data;
+
+      meta_kms_result_listener_notify (listener, feedback);
+      meta_kms_result_listener_free (listener);
+    }
+  g_list_free (result_listeners);
+
   meta_kms_update_free (update);
 
   return feedback;