onscreen/native: Defer posting if there's already a post in progress

And when the number of pending posts decreases we know it's safe to submit
a new one. Since KMS generally only supports one outstanding post right now,
"decreases" means equal to zero.

(cherry picked from commit bce609b3867e3a33948d257dba43791481d4b533)
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1441>
Signed-off-by: Mingi Sung <sungmg@saltyming.net>

src/backends/native/meta-onscreen-native.c

@@ -106,6 +106,7 @@ struct _MetaOnscreenNative
 
   ClutterFrame *presented_frame;
   ClutterFrame *posted_frame;
+  ClutterFrame *superseded_frame;
   ClutterFrame *next_frame;
 
   struct {
@@ -120,6 +121,9 @@ struct _MetaOnscreenNative
   } egl;
 #endif
 
+  gboolean needs_flush;
+  unsigned int swaps_pending;
+
   gboolean frame_sync_requested;
   gboolean frame_sync_enabled;
 
@@ -142,7 +146,11 @@ G_DEFINE_TYPE (MetaOnscreenNative, meta_onscreen_native,
 static GQuark blit_source_quark = 0;
 
 static void
-post_latest_swap (CoglOnscreen *onscreen);
+try_post_latest_swap (CoglOnscreen *onscreen);
+
+static void
+post_finish_frame (MetaOnscreenNative *onscreen_native,
+                   MetaKmsUpdate      *kms_update);
 
 static gboolean
 init_secondary_gpu_state (MetaRendererNative  *renderer_native,
@@ -247,6 +255,7 @@ notify_view_crtc_presented (MetaRendererView *view,
 
   meta_onscreen_native_notify_frame_complete (onscreen);
   meta_onscreen_native_swap_drm_fb (onscreen);
+  try_post_latest_swap (onscreen);
 }
 
 static void
@@ -296,15 +305,13 @@ page_flip_feedback_ready (MetaKmsCrtc *kms_crtc,
   CoglFramebuffer *framebuffer =
     clutter_stage_view_get_onscreen (CLUTTER_STAGE_VIEW (view));
   CoglOnscreen *onscreen = COGL_ONSCREEN (framebuffer);
-  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
   CoglFrameInfo *frame_info;
 
   frame_info = cogl_onscreen_peek_head_frame_info (onscreen);
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
 
-  g_warn_if_fail (!onscreen_native->posted_frame);
-
   meta_onscreen_native_notify_frame_complete (onscreen);
+  try_post_latest_swap (onscreen);
 }
 
 static void
@@ -375,6 +382,7 @@ page_flip_feedback_discarded (MetaKmsCrtc  *kms_crtc,
 
   meta_onscreen_native_notify_frame_complete (onscreen);
   meta_onscreen_native_clear_posted_fb (onscreen);
+  try_post_latest_swap (onscreen);
 }
 
 static const MetaKmsPageFlipListenerVtable page_flip_listener_vtable = {
@@ -435,18 +443,39 @@ custom_egl_stream_page_flip (gpointer custom_page_flip_data,
 }
 #endif /* HAVE_EGL_DEVICE */
 
-void
+static void
-meta_onscreen_native_dummy_power_save_page_flip (CoglOnscreen *onscreen)
+drop_superseded_swap (CoglOnscreen *onscreen)
 {
   CoglFrameInfo *frame_info;
+  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
 
-  meta_onscreen_native_swap_drm_fb (onscreen);
+  if (onscreen_native->swaps_pending <= 1)
+    return;
+
+  onscreen_native->swaps_pending--;
+
+  g_clear_pointer (&onscreen_native->superseded_frame, clutter_frame_unref);
 
   frame_info = cogl_onscreen_peek_tail_frame_info (onscreen);
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
   meta_onscreen_native_notify_frame_complete (onscreen);
 }
 
+void
+meta_onscreen_native_dummy_power_save_page_flip (CoglOnscreen *onscreen)
+{
+  drop_superseded_swap (onscreen);
+
+  /* If the monitor woke up in the 100ms between this callback being queued
+   * and dispatched, and the shell is fully idle (has nothing more to swap)
+   * then we just woke to an indefinitely black screen. The only saving grace
+   * here is that shells usually have multiple frames they want to display
+   * soon after wakeup. But let's not assume that's always the case. Fix it
+   * by displaying the last swap (which is never classified as "superseded").
+   */
+  try_post_latest_swap (onscreen);
+}
+
 static void
 apply_transform (MetaCrtcKms            *crtc_kms,
                  MetaKmsPlaneAssignment *kms_plane_assignment,
@@ -1332,12 +1361,38 @@ swap_buffer_result_feedback (const MetaKmsFeedback *kms_feedback,
     g_warning ("Page flip failed: %s", error->message);
 
   frame_info = cogl_onscreen_peek_head_frame_info (onscreen);
-  frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
 
+  /* After resuming from suspend, drop_superseded_swap might have done this
+   * already and emptied the frame_info queue.
+   */
+  if (frame_info)
+    {
+      frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
       meta_onscreen_native_notify_frame_complete (onscreen);
+    }
+
   meta_onscreen_native_clear_posted_fb (onscreen);
 }
 
+static void
+assign_next_frame (MetaOnscreenNative *onscreen_native,
+                   ClutterFrame       *frame)
+{
+  CoglOnscreen *onscreen = COGL_ONSCREEN (onscreen_native);
+
+  if (onscreen_native->next_frame != NULL)
+    {
+      g_warn_if_fail (onscreen_native->superseded_frame == NULL);
+      drop_superseded_swap (onscreen);
+      g_warn_if_fail (onscreen_native->superseded_frame == NULL);
+      g_clear_pointer (&onscreen_native->superseded_frame, clutter_frame_unref);
+      onscreen_native->superseded_frame =
+        g_steal_pointer (&onscreen_native->next_frame);
+    }
+
+  onscreen_native->next_frame = clutter_frame_ref (frame);
+}
+
 static const MetaKmsResultListenerVtable swap_buffer_result_listener_vtable = {
   .feedback = swap_buffer_result_feedback,
 };
@@ -1452,14 +1507,14 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
 #endif
     }
 
-  g_warn_if_fail (!onscreen_native->next_frame);
+  assign_next_frame (onscreen_native, frame);
-  onscreen_native->next_frame = clutter_frame_ref (frame);
 
   clutter_frame_set_result (frame,
                             CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
 
   meta_frame_native_set_damage (frame_native, rectangles, n_rectangles);
-  post_latest_swap (onscreen);
+  onscreen_native->swaps_pending++;
+  try_post_latest_swap (onscreen);
   return;
 
 swap_failed:
@@ -1469,7 +1524,7 @@ swap_failed:
 }
 
 static void
-post_latest_swap (CoglOnscreen *onscreen)
+try_post_latest_swap (CoglOnscreen *onscreen)
 {
   CoglFramebuffer *framebuffer = COGL_FRAMEBUFFER (onscreen);
   CoglContext *cogl_context = cogl_framebuffer_get_context (framebuffer);
@@ -1479,6 +1534,8 @@ post_latest_swap (CoglOnscreen *onscreen)
   MetaRendererNative *renderer_native = renderer_gpu_data->renderer_native;
   MetaRenderer *renderer = META_RENDERER (renderer_native);
   MetaBackend *backend = meta_renderer_get_backend (renderer);
+  MetaBackendNative *backend_native = META_BACKEND_NATIVE (backend);
+  MetaKms *kms = meta_backend_native_get_kms (backend_native);
   MetaMonitorManager *monitor_manager =
     meta_backend_get_monitor_manager (backend);
   MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
@@ -1493,16 +1550,43 @@ post_latest_swap (CoglOnscreen *onscreen)
 
   COGL_TRACE_SCOPED_ANCHOR (MetaRendererNativePostKmsUpdate);
 
+  if (onscreen_native->next_frame == NULL ||
+      onscreen_native->view == NULL ||
+      meta_kms_is_shutting_down (kms))
+    return;
+
   power_save_mode = meta_monitor_manager_get_power_save_mode (monitor_manager);
   if (power_save_mode == META_POWER_SAVE_ON)
     {
+      unsigned int frames_pending =
+        cogl_onscreen_get_pending_frame_count (onscreen);
+      unsigned int posts_pending;
       int n_rectangles;
       int *rectangles;
 
+      g_assert (frames_pending >= onscreen_native->swaps_pending);
+      posts_pending = frames_pending - onscreen_native->swaps_pending;
+      if (posts_pending > 0)
+        return;  /* wait for the next frame notification and then try again */
+
       frame = clutter_frame_ref (onscreen_native->next_frame);
       frame_native = meta_frame_native_from_frame (frame);
       n_rectangles = meta_frame_native_get_damage (frame_native, &rectangles);
 
+      if (onscreen_native->swaps_pending == 0)
+        {
+          if (frame_native)
+            {
+              kms_update = meta_frame_native_steal_kms_update (frame_native);
+              if (kms_update)
+                post_finish_frame (onscreen_native, kms_update);
+            }
+          return;
+        }
+
+      drop_superseded_swap (onscreen);
+      onscreen_native->swaps_pending--;
+
       kms_update = meta_frame_native_ensure_kms_update (frame_native,
                                                         kms_device);
       meta_kms_update_add_result_listener (kms_update,
@@ -1528,7 +1612,7 @@ post_latest_swap (CoglOnscreen *onscreen)
     }
 
   COGL_TRACE_BEGIN_ANCHORED (MetaRendererNativePostKmsUpdate,
-                             "Meta::OnscreenNative::post_latest_swap#post_pending_update()");
+                             "Meta::OnscreenNative::try_post_latest_swap#post_pending_update()");
 
   switch (renderer_gpu_data->mode)
     {
@@ -1730,13 +1814,24 @@ meta_onscreen_native_direct_scanout (CoglOnscreen   *onscreen,
       return FALSE;
     }
 
+  /* Our direct scanout frame counts as 1, so more than that means we would
+   * be jumping the queue (and post would fail).
+   */
+  if (cogl_onscreen_get_pending_frame_count (onscreen) > 1)
+    {
+      g_set_error_literal (error,
+                           COGL_SCANOUT_ERROR,
+                           COGL_SCANOUT_ERROR_INHIBITED,
+                           "Direct scanout is inhibited during triple buffering");
+      return FALSE;
+    }
+
   renderer_gpu_data = meta_renderer_native_get_gpu_data (renderer_native,
                                                          render_gpu);
 
   g_warn_if_fail (renderer_gpu_data->mode == META_RENDERER_NATIVE_MODE_GBM);
 
-  g_warn_if_fail (!onscreen_native->next_frame);
+  assign_next_frame (onscreen_native, frame);
-  onscreen_native->next_frame = clutter_frame_ref (frame);
 
   meta_frame_native_set_scanout (frame_native, scanout);
   meta_frame_native_set_buffer (frame_native,
@@ -1983,22 +2078,79 @@ meta_onscreen_native_finish_frame (CoglOnscreen *onscreen,
   MetaKmsDevice *kms_device = meta_kms_crtc_get_device (kms_crtc);
   MetaFrameNative *frame_native = meta_frame_native_from_frame (frame);
   MetaKmsUpdate *kms_update;
+  unsigned int frames_pending = cogl_onscreen_get_pending_frame_count (onscreen);
+  unsigned int swaps_pending = onscreen_native->swaps_pending;
+  unsigned int posts_pending = frames_pending - swaps_pending;
 
-  kms_update = meta_frame_native_steal_kms_update (frame_native);
+  onscreen_native->needs_flush |= meta_kms_device_handle_flush (kms_device,
-  if (!kms_update)
+                                                                kms_crtc);
+
+  if (!meta_frame_native_has_kms_update (frame_native))
     {
-      if (meta_kms_device_handle_flush (kms_device, kms_crtc))
+      if (!onscreen_native->needs_flush || posts_pending > 0)
-        {
-          kms_update = meta_kms_update_new (kms_device);
-          meta_kms_update_set_flushing (kms_update, kms_crtc);
-        }
-      else
         {
           clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_IDLE);
           return;
         }
     }
 
+  if (posts_pending > 0 && swaps_pending == 0)
+    {
+      g_return_if_fail (meta_frame_native_has_kms_update (frame_native));
+      g_warn_if_fail (onscreen_native->next_frame == NULL);
+
+      g_clear_pointer (&onscreen_native->next_frame, clutter_frame_unref);
+      onscreen_native->next_frame = clutter_frame_ref (frame);
+      clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
+      return;
+    }
+
+  kms_update = meta_frame_native_steal_kms_update (frame_native);
+
+  if (posts_pending > 0 && swaps_pending > 0)
+    {
+      MetaFrameNative *next_frame_native;
+      MetaKmsUpdate *next_kms_update;
+
+      g_return_if_fail (kms_update);
+      g_return_if_fail (onscreen_native->next_frame != NULL);
+
+      next_frame_native =
+        meta_frame_native_from_frame (onscreen_native->next_frame);
+      next_kms_update =
+        meta_frame_native_ensure_kms_update (next_frame_native, kms_device);
+      meta_kms_update_merge_from (next_kms_update, kms_update);
+      meta_kms_update_free (kms_update);
+      clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_IDLE);
+      return;
+    }
+
+  if (!kms_update)
+    {
+      kms_update = meta_kms_update_new (kms_device);
+      g_warn_if_fail (onscreen_native->needs_flush);
+    }
+
+  if (onscreen_native->needs_flush)
+    {
+      meta_kms_update_set_flushing (kms_update, kms_crtc);
+      onscreen_native->needs_flush = FALSE;
+    }
+
+  post_finish_frame (onscreen_native, kms_update);
+
+  clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
+}
+
+static void
+post_finish_frame (MetaOnscreenNative *onscreen_native,
+                   MetaKmsUpdate      *kms_update)
+{
+  MetaCrtc *crtc = onscreen_native->crtc;
+  MetaKmsCrtc *kms_crtc = meta_crtc_kms_get_kms_crtc (META_CRTC_KMS (crtc));
+  MetaKmsDevice *kms_device = meta_kms_crtc_get_device (kms_crtc);
+  g_autoptr (MetaKmsFeedback) kms_feedback = NULL;
+
   meta_kms_update_add_result_listener (kms_update,
                                        &finish_frame_result_listener_vtable,
                                        NULL,
@@ -2021,7 +2173,6 @@ meta_onscreen_native_finish_frame (CoglOnscreen *onscreen,
   meta_kms_update_set_flushing (kms_update, kms_crtc);
   meta_kms_device_post_update (kms_device, kms_update,
                                META_KMS_UPDATE_FLAG_NONE);
-  clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
 }
 
 static gboolean
@@ -2929,6 +3080,7 @@ meta_onscreen_native_dispose (GObject *object)
   meta_onscreen_native_detach (onscreen_native);
 
   g_clear_pointer (&onscreen_native->next_frame, clutter_frame_unref);
+  g_clear_pointer (&onscreen_native->superseded_frame, clutter_frame_unref);
   g_clear_pointer (&onscreen_native->posted_frame, clutter_frame_unref);
   g_clear_pointer (&onscreen_native->presented_frame, clutter_frame_unref);